Saturday, 2 November 2013

Tuner Fishing

Finally, today ive had a few moments free to complete the wiring of the copy RT-remote unit needed for my new LDG RT-11 remote Auto-ATU. However, it does seem that i've not got it completely right!



It doesnt look too bad, ok so the holes for the switches are a little big, but its so tight in the box I couldnt get the buttons through otherwise! And its very compact, I think probably a little smaller than the LDG original
A possible improvement with mine over the original is the buttons ive used, each has its own built on little green LED. I havent connected them, but that may be an option in the future if I find having them backlit for night use might be useful.

At first however, I couldnt get anything to operate! After a while I realised that, since I hadnt marked the controls up, I had put it into some odd mode without knowing. Starting again, I managed to get some control from the box only, without the Alinco connected (other than for power). I soon realised that I had the VSWR OK and TUNING LEDs transposed, not much of a problem, but I did want red to show tuning in progress and green to show good SWR, so I later swapped these over.

The RT-11 is set up, with this control box, on the shack desk, with the RF from the Alinco going  via the MFJ manual tuner, in bypass mode, to the RT-11. This allows me to monitor whats going on on the MFJs SWR meter. Since the first PL259 patch lead I found was a 5m RG-213, Its a tad untidy

Ive tried the RT-11, and the control box, at 10w from 80m up to 10m, on my doublet, and the RT-11 has so far matched the lot!

The only problem now is that the control from the Alinco DX-70TH is not functional. Im pretty sure this will be a simple wiring problem, Ive probably got a couple of the connections the wrong way around. I'll maybe sort this tomorrow.

Ive made good progress on dismantling that old 120kHz test set as well, since Julie has been nagging me to do so, and salvaged a lot of good parts from it. Trouble is, now I need to go through all the salvaged components and test them and put them in their correct containers! Probably the most useful things to have come from this though are the brass nuts and bolts, as these will solder into PCB material boxes to make good mounting fixtures.

I need to add some suitable labels to the RT control box. These will just be hand written, but on a white background so I can actually read them! Although the RT-11 and the RBA-4 are weather proof, I need to get a IP rated housing for them, as there may also be a switching system to add a loop of extra 450ohm ladder to improve the match, and perhaps a relay to link the two sides to make a T for topband use. Both the tuner and the balun will be mounted with wing nuts, so they can be easily disconnected when needed for field/SES use.

Wednesday, 30 October 2013

QRPme SBSS and VLF

One of the items I was pleased to obtain at Rishworth, were a pair of QRPme SBSS clamps. Getting them involved ensuring the cost had been covered by my junk sales, and then being roundly questioned by the proprietor of QRPme over my choice of T-shirt and lack of hat. Now, these clamps are not cheap, at £20 for the pair, but they are remarkably good at what they are for, namely building PCB material boxes. Having bought them, I was very impressed to be shown the original Tuna Tin transmitter built by Doug DeMaw, and kept safe in a wooden box. I was also happy to receive a few free MeSquares and MePads!

The clamps themselves of course are no help if you do a shoddy job of cutting the board to start with, so I was very, very careful to mark and scribe the board prior to cutting. I did make the mistake of not correcting for the board thickness, but that was soon rectified. Using one of the SBSS clamps, I soon had a little 1" x 1.5" box built, in which to rebuild my little VLF to soundcard interface





The picture shows it with the sockets installed. The one big mistake I did make, is that after marking around the washer of the earth terminal, I then forgot to measure the diameter hole needed for the body, and drilled it out the full width of the washer! Luckily, the blue terminal post just stayed in place in that hole (well tightened!) so it wasnt too bad a disaster.

Much effort went into trying to solder nuts in to attach the lid, but they just wouldnt hold. Eventually a pair of hex posts did solder in, but its a loose fit as I dont have any screws of the right thread.

The VLF interface is about the simplest receiver that can be made, simpler really than even a crystal set. It really consists of little more than an antenna wire connection to a soundcard input via a blocking capacitor. My version is a tad more complex, as it also includes three levels of protection - there is a 100k resistor to ground to bleed off static buildup on the antenna; a pair of back-back Germanium diodes that will clip the incoming signal above about 0.3v; and now a small wire ended Neon lamp acting as a gas discharge protector

Next job is to complete the RT-remote clone, which just requires the internal wiring loom completing, so I can then test, and indeed control, the LDG RT-11 Remote Auto-ATU.

Saturday, 26 October 2013

Rishworth

These past few weeks have been a big effort to offload junk and obtain useful, desired items. This all started when an LDG RT-11 Remote Auto-ATU appeared on ebay, something ive been after for some time. This duly bought, I needed to recover the cost, and set about selling stuff off. The RT-11 cost was covered by the sale of a surplus DSP module. A cheque from the Lions in payment for costs for the show was gratefully received, which will cover the QSL cards print costs, some station clocks, and the balun to go with the RT-11. Its also paid for the specialist cable from the Alinco DX-70 to the ATUs remote control box.

But, I dont have the remote control box! So, Im in the process of building a copy. As its literally three buttons, two LEDs and some sockets, its not too hard, apart from cutting the holes in the box neatly! The DB9 connector will be the awkward part.

The few parts I needed but didnt have I picked up today at the G-QRP club convention at Rishworth. I took all my heavy junk to try and sell on the bring and buy, and set off really early to get parked as close as possible. Well, I still ended up parked about as far away as it was possible to be, and accepted some assistance carrying the stuff in. In all most of it sold, netting me £45. I'd taken £50 with me, and after all what I bought, which included a pair of the little vice thingies from QRPme (for building PCB material boxes), a club mug, some slide rules, raffle tickets (not winners) and lunch, I came home with £55 in my wallet! Switched to 17m from 20m on way home to get away from the contest, and added a few QSOs to my mobile tally, including Cyprus. Not quite as good as Lebanon the day before. I now have a 40m antenna for the car, but havent perfected the match yet.


Sunday, 13 October 2013

Where It All Began, Pt 1

I dont really know why i'm doing this post, but for some odd reason I feel the need to relate my history, my amateur radio journey, so to speak.  Its im sure nothing exceptional or remarkable, but its been part of my life since school and its whats ultimately led me to the career im now in. So for what its worth, while im not actually able to do any decent radio work due to shifts for the next couple of weeks, i'll tell my tale here,

Somewhere back in the dim and distant past, around the age of thirteenish, i'd got interested a bit in computers, back then these were 8 bit machines like the Electron and Commadore. I myself had a Sinclair Spectrum +3, 8bit and a whopping 128k of RAM, plus a mental 3inch 'floppy' drive that Sir Clive must have found being given away with far eastern cereals. I was introduced by a friends dad to a local computer club. This was held in a back room of the old Corporation Brewery Taps, in Doncaster. I didnt find it that enthralling to be honest. I'd already realised it was the nuts and bolts rather than the software that interested me.

Somehow, when trying to find electronic components, it had been suggested to me to go on a coach trip with a local amateur radio club to the big radio rally at Drayton Manor. I got permission to go on the trip, and pitched up at the appointed time  at a pick up spot near the supermarket in Edenthorpe. There were a few other people waiting. Particularly, there was a bearded chap and his wife and daughter. This was Eric, G0PAQ, his wife Janet, and daughter Samantha. Being a hormonal adolescent I of course instantly fancied Samantha, who was several years older than me, but it was her dad Eric that who was to start me on my journey into amateur radio.

The trip to Drayton was a real eye opener for me. All the components I could ever imagine, flea market stalls selling anything and everything radio. I bought a huge keyboard that I was convinced was full of goodies (it was just a load of scrap steel!), and half a £5 bag of LEDs for £2 (all I had left), which proved to be about a thousand 3mm LEDs! I also saw the big name stalls like Martin Lynch and Nevada,a dn the shiney new radios.

Now, I have to confess to not being entirely devoid of any hint of radio knowledge. I had a Saisho world band receiver, and listened late in the evening to all manor of stations of shortwave. I sent reception reports in, and got back QSL cards and schedules from the likes of Radio Helsinki, Radio Sofia etc. And there was always, from my bedroom window, the tantalising glimpse of the bizarre aerial at the end of the road! A huge, spider web of wires on a lattice tower, stood in someones back garden...

Following Drayton, Eric suggested I came to the club. This was Mexborough and District Amateur Radio Society. They met on friday evenings, and I could get a lift, along with Eric, from John Dennis, who was Erics fellow plant electrician at International Harvesters. I was told to be at Erics at about half six, if I remember, the following friday...


Tuesday, 1 October 2013

Loopy Earth? Ghosts in the machine?

Bollocks!

This carrier balance thing, its driving me mad. Even more so, after this mornings experiments. Nothing I do reduces the carrier level. A mock up mixer didnt show the problem either.

But, a change of probe due to a slightly iffy BNC connector resulted in this interesting spectrum

 Its not the display itself thats interesting here, but look where the probe is! The circuit is over two feet from the analyser, and the probe is not connected at all!

The only things connected to the circuit are the PSU, the Bird dummy load,a nd the AF lead from the Marconi 2955. Wrapping the power leads around a ferrite rod made no difference. Turning the AF generator output on and off made no difference (except to the sidebands), but turning the Marconi itself off, or disconnecting the AF lead, did! The carrier vanished!

It looks like ive hit a serious case of the Gremlins!

Next step then eliminate the 2955 - so I need now either a battery powered AF generator, or to mock up a tone circuit



Monday, 30 September 2013

Balancing Act

Several tricks have been tried with the 10m Wispy to try and get the carrier balance right, so far none have been entirely successful. A balance control potentiometer had no effect at all, and changing the diodes seemed to have no effect either. So, I reverted the circuit back to its original form, put a pot in place of R11 to make it adjustable again, and totally rewound T2, physically symmetrically. An RF bypass capacitor has also been put on the AF modulation input

Things do seem a little improved. The carrier is still present, but I can get it at least to look more like DSB should do. Adjusting R11 for best 2nd harmonic resulted in what looks to me to be a sensible spectra for a doubler. The 28MHz 2nd harmonic is dead center, the first two peaks from the left are an image of the 14MHz fundamental, and the machines zero marker

The harmonics are in the form of a 'staircase' going down in relative strength. Adjusting now for best carrier balance at the mixer output, I managed to get the signal looking like this

Yes, its much weaker than the doubler, but I suppose taking into account the differences from changing the analyzer settings, and the insertion loss of the mixer, and the likely mismatch between the analyzer and the input to the driver where this signal was taken, it at least shows that the carrier is down on the sidebands. This is with a 10kHz 50mV AF input. 10kHz is needed to be able to see the sidebands apart from the carrier on this machine. Looking again at the doubler, shows that when set for best carrier null, it isnt quite as good an output on the 2nd harmonic, and the 3rd isnt down as far as it was

Putting the probe now to the output of the PA, just after the Low Pass Filter, we see an amplified DSB signal, still with significant carrier though. Whether this is good enough for on-air use I dont yet know. Im not certain by how much I should expect the carrier to be suppressed, Roger claimed 30dBm, mine I think is about 14dB down, assuming im reading the scale properly!

I shall have to make a point of listening to the output on a general coverage receiver in SSB mode to see how noticeable the carrier is. The 3rd harmonic isnt very well suppressed either, being barely below the wanted second, but interestingly its carrier is almost none existent!  There are also more noticeable extra mixer products. The picture isnt so good as the camera captured the interval of the sweep time! but the upper sideband can be made out

The 3rd harmonic then needs looking at, perhaps making the driver and PA inductors as tuned circuits will help here. I could not observe any greater harmonics though.

Next step then I think is to sort out the biasing on the driver and PA, so they dont get so hot, and to measure the output power, see if it really is producing what it should be! But these are probably all tasks for another day.

Sunday, 29 September 2013

Muppet Show

Got the Larkspur mast guying kit out for inspection today. The valise needs a new sheet of plywood gluing in over the original, which is split, but other than that its not in bag nick really. Now have eight guy lines, but only one base plate pin. The ground spike and base plate that came with it are not much use, so have been replaced with those I already had. I might think about putting the mast up for a test tomorrow.

Building the RF diode probe proved rather simple this morning, and the pen selected was spot on for it. Cutting off the tip a little earlier than the main body left a gap the same diameter as the body of the cut down test probe, which fit in snug, held in place with a dab of superglue.


A small hole was bored through the side wall for the ground clip, and the end cap was slit and a small hole made for the coax. It was then slipped over the coax and pushed back into place, sealing the end and securing the cable. A pair of 4mm plugs and a couple of quick continuity tests later, and it was ready for testing with RF.


RF testing was accomplished by connecting it to my DVM, and probing the BNC output connector of my Marconi 2955B communications test set. With the BNC selected, it will give an RF output up to +5dBm. A quick run through at 28MHz allows comparison with the signals on the 10m WSPR unit -

0dBm = 0.38v                 3dBm = 0.56v
1dBm = 0.44v                 4dBm = 0.63v
2dBm = 0.49v                 5dBm = 0.72v

Of course, these are at 50ohms, so the readings in-circuit wont be exactly the same.

After much testing with parallel capacitors on the doubler stage of the wispy, I finally managed today to get a very high 28MHz output with virtually no 14MHz or 42MHz component. Very good I thought, er, no, actually! When I applied modulation, all I got was a very good AM signal! Whats going on? It turns out i'd forgotten to move the probe from the spectrum analyser from the output of the mixer back to the collector of T2, the doubler transistor!

So, all the work to get the parallel capacitance right is in fact wrong. That all needs to be redone now. I also noticed that the driver stage isnt, it appears to have unity gain, what goes in comes out no bigger. It also gets rather hot for a 2N3904! Something then is definately not right there.

So ive decided to go back to the start and work forward, solving any issues as I come to them. Using my nice new diode probe, I find the output of the oscillator is 0.38v, about 0dBm, or 1mW. The output of the doubler is a touch higher at 0.52v, about 2.5dBm or 1.8mW. This seems low to me, im not sure what the insertion loss of the mixer is, but I bet its more than 2.5dB! Measuring at the crystal itself showed 0.79v, about 5.8dBm or 3.8mW.

So, the questions are - what level output should I be expecting from the oscillator and the doubler? What loss must be overcome in the mixer? What level drive does the mixer need? And, why am I not getting those figures?

Im also concerned about the balance of the mixer. After a lot of searching on the tinterweb, ive finally found a similar design that shows a value for a balance resistor, at 200ohm. Im pretty sure I dont have any 200ohm presets though. Theres also a hint that the insertion loss might be about 8dB.

Saturday, 28 September 2013

Probe Plan

I really should have done this a long time ago, but these past few days working on the 10m beacon have shown just how much I need a diode RF probe. So, construction has started on one, now I have some suitable diodes. To be honest, the idea was in my mind yesterday, which is why I picked up quite a few 1N34s.

What has always stopped me was the difficulty I found in building the actual probe part, but I decided to sacrifice one of an old pair of meter probes. The next trouble is a suitable barrel to house it all in. A felt tip pen in my pen pot turns out to be the ideal dimensions. With the probe cut down, and a small twin strip bit of veroboard soldered on, its now ready for the components to be mounted tomorrow





It turned out that the probe rod went the entire length of the probe body, so when I find the rest (somewhere on the shelf where it landed after cutting off!) theres enough to make a few more!

As I was finding this picture out from where the PC had saved it, I spotted again an old mugshot of yours truly in the act of calmly knackering the UKs telly

I think this is a few years old, the two telemetry screens are TMC and ARQOSS, so its prior to the final DSO. Im only actually knacking up Scotland and Northern Ireland there.

Friday, 27 September 2013

National Hamfest

Set off early for the National Hamfest this morning, should have been a nice quick run, but several accidents meant detours, one of which from off the A616, I had no idea where to go, but a local window installers van was in front of me, so I followed him! Arrived only about half an hour after opening, so wasnt too bad.

After paying in, which at a fiver I do think is a bit steep, especially since, despite this being our 'National' rally, its still not a patch on rallies of my early radio days such as Elvington and Drayton, I decided to do my usual 'tour' and take a look at everything before starting to shop. My plan soon went awry, when spotted beside a stall with a few PRC-320s on, was this


an almost complete, to CES, guying kit for the 27ft Mk1 Larkspur mast! Its missing a guy rope, the elusive spanner, and the 4lb hammer, but it does include the guy pegs ive so desperately been searching for, and the base insulator, plus a brand new, unissued, 1976 dated instruction plate! Now, ive seen these go for £40 on ebay without the pegs, so I set myself a £30 limit, and asked the stallholder how much "well, I was going to ask a fiver per item" says he, "or, £15 for the lot", well, I couldnt get a twenty quid note out fast enough!

But, it did give me one small problem - i'd been there under ten minutes and was already carrying a very heavy bag! So I obtained a pass out stamp on my hand and took it all to the car, before heading back in to start over again.

Although reasonably small still, it was none the less interesting, i'd have prefered to see more junk than computer stuff, but there wasnt too much computer kit. Some very nice masts which I can only admire, and even met one of our field engineers, who ive bossed about at daft o'clock, but never met. I managed to avoid the cup cake stall, although I was very tempted! and concentrated on getting what id gone for. Well, several 2nd hand N-types at 50p a pop filled that quota, 1N34 and 1N4148 diodes from Bowood, and the main items were accounted for. One stall had little sealed bags at a pound with a selection of trimmer capacitors in them, so some of those went in the bag. I took a bit of a punt on a 50p valve socket that may or may not have been the right one for the dekatrons, not as it turned out!

I also wanted some single sided PCB material as im running low. Most stalls with this were charging upwards of £2.40 for a 4" x 6" sheet. Whilst traversing the car boot, I spied some big sheets of it right at the back of a stall. These turned out to be double sided, but were something like 6" x 30" at least! I wasnt too keen at first, being double, as its a hassle taking one side of copper off, but when I asked the price and was told "20p a chunk", well you cant pass up a bargain like that! I bought five for a quid, and as you can see, it really was a bargain


My only 'frivolous' purchase was a little antenna, supposedly a dual 2m/70cm, according to the stall holder. Im not convinced, as its under a foot long, but he wanted a pound, and accepted the remains of my change, which was 90p! I'll need to test it somehow and find out what frequencies it works on. I also bought an antenna base spring for 50p, which might not be strong enough for the big HF whips, but im sure will hold a 10 or 12m antenna


Once home, via a well awaited Tower burger meal (large with Pepsi), I was very pleased to find my copy of Sprat awaiting me on the doormat. I could now turn my attention back to the 10m Wispy.

Firing it up, and looking at the spectra on the output of the mixer, I can clearly see that the fundamental, plus the third and fifth harmonics, are present along with the 28MHz signal, albeit at a somewhat reduced level. Setting the spectrum analyser up for observing the modulation, I can now see that the 28MHz signal is showing DSB, and the 3rd and 5th harmonics are much more AM like.

Curious as to whether im getting the maximum 28MHz signal, I looked again at my setup. Rogers original design stated 60pF trimmer, and I have a 35pF trimmer in parallel with a 33pF fixed cap. But, is it enough? The key to that would be if the trimmer was set at maximum. But these little ceramic ones are not easy to work that out with. So, taking my capacitance meter and the rest of the bag, I tested several, setting them to maximum and marking them. Maximum it turns out coincides with the top plates center being aligned with the single pin. Looking at my setup on the Wispy, it is indeed at maximum. I have a feeling that adding a bit more parallel capacitance will give me a bigger 28MHz peak, and allow me to gain that peak at a mid-range position. But thats a task now for another day.

Thursday, 26 September 2013

DSB finally

Working today on the 10m Wispy transceiver, which is the design here

After a lot of headscratching, discussion with others etc, it looks like im finally getting somewhere with it. The odd phenomenon of the 42MHz AM output started me investigating the doubler stage further. I then noticed that C16, 35pF in this design, was marked as 60pF in the original Tx only version. 42MHz is the 3rd harmonic of 14MHz, was the stage working as a tripler instead? Patching 15pF across C16 brought the 2nd harmonic peak up more than the 3rd, whereas before they were equal. Hmmm, lets try 33pF in parallel then, lo and behold, an even bigger 2nd harmonic peak! Switching back then to probe the  output of the mixer, I see this
a 28Mhz double sideband signal! At last! OK, so the carrier suppression isnt very good yet, but its DSB, and at this stage thats whats important. I can now tidy this signal up, and start getting the amplifiers up and running properly.

Spreading the spectrum

The 10m WSPR beacon still causes me headaches. After a lot of twiddling, and much technical advice from Ken G8BEQ (Thanks Ken!) I realised a mistake i'd made with the bias setting of the doubler, and now once again have some sort of signal from it. The modulator however, continues to give trouble. There seems to be no carrier balance at all, all the 28MHz LO in all comes out, AF input or not. So, I have added a preset resistor to try and null the carrier.

Before I can sensibly try it though, I need to get around the problem of observing the spectrum properly on the spectrum analyser. Thanks to Bob G3OOU, I now know how to set the analyser up for this, although it shows that the machine is rather drifty! (either that or the 2955 is!). It seems that since the machines minimum span is 100kHz, I need to really give it some welly with a modulation frequency if at least 10kHz to be able to make the spectrum spread out over a few divisions. Now I know this, I can give the WSPR transceiver 10 or 15kHz of AF drive and see what the output of the modulator really is doing.

One further thing that Ken has advised me with, is the standing current of the PA section. In the last post I mentioned it was getting too hot even with no drive, well, it seems its dissipating nearly a Watt! This is supposed to be a 200mW output PA! Ken has given me some new bias values to try which bring the standing current down to a mere 20mA. But the PA has to wait, the modulation needs sorting first!

I still have my doubts about either the transformer or the diodes. Its the National Hamfest tomorrow, so if im able to go, i'll get some proper OA91 or 1N34s!

Rang Geoff at Castle Electronics today, my FT-857D is repaired and ready. RF preamp transistor, set of IF filters and a few PIN diodes needed changing. Learnt an interesting trick from Geoff on using both antenna ports to see if the front end streering diodes are leaky. Should have the rig back mid week (being sent to work) so finally back on air HF mobile!

Thursday, 19 September 2013

Transformer Troubles

Well, much Rf work was put aside for some time, whilst the show was got out the way, and the FT-857D was sent of to Geoff at Castle Electronics to be fixed. Also during this time, I myself underwent a 'gentlemans procedure' and all thoughts of radio were off for a few days.

The show was a pretty good success. Operating predominantly on 40m SSB, we made a couple hundred QSOs. 2m FM showed itself as suspected to be pretty much a lost cause. Bob M1BBV and Steve G7TAO both came to help out, and their assistance was very much appreciated, as was the dual band handie from Steve!

So now I can get back to a bit of RF engineering. The Wispy 10m WSPR transceiver is first up for completion. All the transmit side is now built, as can be seen below
But, its not yet operational. With no AF input, im still seeing lots of output, but also lots of harmonics. AF input doesnt seem to have any affect. Although the spectrum analyser says the 28MHz signal is strongest, the Marconi 2955 doesnt register it, but instead shows a few tens of mW at about 43MHz. I suspect that theres a problem with the RF transformer in the mixer. The PA is obviously taking current, as its getting hot, perhaps a bit too hot!

I think the transformer must be the culprit, and i'll take it off and have a look.

Further to the show station, the thought occurs that since were held in the grounds of the Deaf Trust, we should be demonstrating at the station ways in which the hobby can be enjoyed  by those with hearing problems. So, im starting to investigate digital modes, with the idea of operating a digital station next year. It seems either old fashioned RTTY, or PSK31 are the modes to choose.

Wednesday, 7 August 2013

Discone Diva

The discone is now mounted in its final location in the loft. Currently fed via a run of RG-58 with several splices and adapters, but still pulling in VHF and UHF air transmissions. The feedline isnt ideal, calculated loss is about 2.8dB at 300MHz. So, Sam and I spent a little time yesterday running a nice tidy new length of Times Fibre TFC-10 CATV coax. Although this is 75ohm, its loss at 300MHz is a mere 0.85dB, a considerable improvement, and anyway, a sweep of the discone with the antenna analyzer revealed its resonant much closer to 75 than 50 ohm. The cable still needs connectors installing, but it should be a great improvement.

The FT-857D looks like it might be a much harder job than I can manage. The parts that would need changing are tiny, well beyond my soldering kit, so its all down to whether my previous boss will allow me to make use of his workshops SMT stations. As a result of this job, ive not even started the show antennas. I have a feeling were going to be limited on the bands this year! Still, being indoors means we should get more operating time, and having mobile internet now means I can establish out frequency on the 'net.

Also, to compound matters, the main PC failed yesterday. Getting this back online, or replaced and its data recovered, is much more a priority than anything else im afraid.

Friday, 2 August 2013

Hard or soft?

Ive been told, that the FT-857D had a tendency to drop some of its firmware alignment values. It seems that this has been known to cause the poor receive issues im having by corrupting the first few parameters. So, I have a list of 'typical' alignment values, and later today I will run through the alignment menu and see if what my radio has in its memory is close to the values to be expected.

With any luck, the problem will turn out to be a software corruption that can be rapidly sorted out, and not a hardware failure necessitating fiddly SMT rework.

Amazingly, the Discone antenna was awaiting me in the Goods In/Out room when I arrived at work yesterday evening. Exceptional, since it was free delivery, and all in cost over £15 less than any other sellers, to have arrived literally 'next day'.

Inspecting the antenna, it seems reasonably well built, with a stainless steel hub, but the 5mm diameter elements are aluminium, as is the support mast. Since i'm intending using this in the loft, this is of no real concern. For the time being it will feed down to the shack by RG-58 coax, not ideal at UHF over the length of run, but I already have it in position. I 'may' have some RG-214 with pretty manky sheathing that can be used instead, if its long enough. Another possibility is to use a run of some of the CATV coax I have, but i'll have to consider the impedence mismatch in that case.

It will be interesting to sweep this antenna with the analyzer. The manufacture claims a bandwidth of 25-1300MHz. Doubtful. Putting the dimensions into an online calculator, I get a minimum frequency of 90Mhz. However, I dont know the parameters for the bandwidth, it may be in that calculator a VSWR <1.5:1, whereas i'm happy to work on a 2:1 bandwidth, even more for receive only purposes. If the VSWR is 1.5:1 or less at 70MHz and 145MHz then i'll be happy with that for transmission purposes. I'll put my findings up on here.

Thursday, 1 August 2013

By Heck, Its All Gone Quiet!

Its been a while since I posted on here, mostly this is due to having gone on holiday. So, not much has progressed. Both the 10m WSPR transceiver and the 4m Transverter are still in progress, but not sufficiently further to report on.

The one big, and annoying, change is that my FT-857D has gone deaf. Tested yesterday and all across HF and 6m is down at -85dBm ish. Ive already got a kit of spare PIN diodes, which im led to believe are the most likely suspects, and I now have a printed and bound copy of the Technical Suppliment, aka Service Manual. This needs repairing pronto as not only is it my mobile rig, it is also due to be the 2nd HF station at the show in under a month.

Also needed for the show is the 2nd HF antenna, in this case a Cobweb. Construction is yet to begin on this. Construction is also due to start on a horizontal antenna for 4m. Ive found that the very thin end section of the fishing poles that will form the spreaders of the cobweb, although no use in that antenna, are perfect to make a little Moxon for 4m!

Ive also finally got around to a solution for 2m FM and for general listening - a new Discone antenna that hopefully will arrive shortly. This will probably be loft mounted, so will be a little down on an outside rooftop location. When its in place i'll run the analyzer across it and report on here if it really does live up to the claims of the manufacturer!

Tuesday, 16 July 2013

Racal Clansman Key

Now, I obtained this quite some time back, along with a nice McMurdo key similar. This is a miniature Morse key complete with webbing strap, to fasten it around the operators leg, and intended for use with Clansman radios.

My example came without a cable, so I needed to open it up and replace the cable and plug. To do this a rubber seal must be removed, along with the knob, which just unscrews. Once opened, a new cable can be easily fed in and connected, and the key can be adjusted.






Some toroid winding was also needed recently, this is the combined doubler/mixer transformer for the transmit stage of the WSPR beacon. It did prove a tad fiddly

More on that to follow, but for various reasons i've not got much done this week.

Monday, 8 July 2013

Ominous Whispers

This afternoons construction session started badly. In trying to remove the key component I desperately need from the old modem it was attached to, I broke it. So, no audio isolation yet. As if anyone but me cares. Occasionally, I wonder whether or not anyone is actually reading all this wittering I post on here, apart from the odd unfortunate soul directed here to look at a picture, from some other forum or group. Not that it matters even remotely, I write this stuff just to have a good moan and put down my thoughts on the projects im working on.

Ive managed to separate all the  transistors from all what I aquired yesterday, all that remains is to actually sort through them and put them away in the appropriate containers. At the moment they are cluttering up my antistatic mat somewhat

  

Despite that, I managed finally to get somewhere with the 10m WSPR beacon transceiver. Now having the right parts, including a few from yesterdays haul, ive managed to complete the build of the 14MHz Local Oscillator. Surprisingly, theres a lot going on on that little Colpitts circuit! With the two output capacitors in place, plus the bypass and decoupling capacitors, its rather a tight little circuit. Powered up, working first time, and showing 14.055MHz, a little tweek of the trimmer capacitor and its now dead on 14.0623Mhz as required for doubling to 10m.

 
The two coupling capacitors can be seen, the one crossing over the black line will feed the Polyakov mixer in the receive chain. The black line separates the transmit chain (upper board) from the receive chain (lower board). All I need to do now is decide whether to build the transmit or receive chains next!

Apart from a few more bench tests on the receive converter, measuring FM SINAD etc, ive done nothing further on the 4m transverter. I might tomorrow rig up an antenna and let it listen on the band for a while, see if I can find anything off-air, whilst I get on with some of the jobs Julie has left for me nearby in the garden.

Sweet Luck Haul

What happens when you pay £8 for the random contents of a big junk box, on the floor at a rally, all because an old medicine bottle in it has a label on that suggests theres a transistor in there, probably worth 50p, that you need?

You hit the bloody jackpot, thats what!

I havent even found the BF199 transistors yet, what I bought it all for, but the sheer quantity of unused, brand new electolytics, ceramics, polyester caps, 4mm plugs, mixed transistors and literally hundreds of bandoliered mixed resistors, means my parts tubs are stocked up on basics for a long, long time to come!





Theres also quite a few vintage resistors and capacitors, a few ICs, some high voltage ceramic disk caps, and a brand new old stock 470kHz IF transformer, including paperwork. Well worth the £8. And I might claw a bit of that back from the vintage bits and bobs. Really wish i'd offered a tenner for this and the box underneath now! A good proportion of the resistors are also the very tiny body ones I think from Philips, which are good for miniature QRP circuits. The big bandolier on the top right of the picture is a mixed run of resistors, links, axial inductors, obviously from an automated production run for something.

I should have given that other fella £2 for that box Sam was rummaging. The 15MHz glass package crystal was nice, but the large number of new, boxed record player styli might have earnt me a good wadge.

If you cant stand the heat, dont be a test set!

After a lot of work and measurements, my Marconi 2955B decided to actually work again today. This is after several peoples advice, lots of measurements, and a good deal of relearning how to properly use an oscilloscope on my part! I also discovered that the unmarked x1/x10 switch on the scope probe I was using is actually the other way, and all my supposed bad measurements had been done on x10.

It seems the problem was ambient temperature, the last few days incredible heat made the workshop almost unbearable to me, and it seems completely unbearable to at least one of the 2955Bs circuits. Today, being considerably cooler, its working perfectly.

Sam came with me yesterday to the Red Rose QRP rally. I'd won Amtools charity auction for the entrance and lunch, but even with Sams round of toast, I think the charity gets the best deal! Still, I had some decent pie and peas and a brew which took most of the time we were there to cool! Picked up a set of telescopic fish poles to use as spreaders for the show cobwebb, IF i manage to get it built in time. I havent finished the Larkspur mast yet, nor tested the 40m antenna. At this rate we'll be falling back on the big fishpole and the link dipole.

Of the list of items I actually wanted, I think I got two. One, the isolation audio transformer, was found on a defunct 56k modem card for 20p. The other, a BF199 transistor, is somewhere in the dozens of transistors and hundreds of resistors I picked up in a £8 deal for the entire contents of a junk box! A bit steep for the transistor, but the box contained two brand new unopened Velleman component packs of electrolytics and ceramic caps, several unopened Tandy ICs of which two at least look to be quite rare, and a nice NOS ATP-4 valve. Thats just what ive dug out so far. The bits that are no use to me I should be able to sell to make a few bob to cover the cost of the box, and perhaps if im lucky make enough to go someway to offset the cost of the cobwebb spreaders.

Two things I do have to sell, are these Pye telecom extender boards -
Ive got no idea what they extend, they look like maybe Pye Olympic or Europa PMR radios. I'll offer them first on the Vintage forum for a couple of quid, someone might have a use for them. Theres a load of unused old Hunts capacitors in the box as well, not sure if anyone will want those!

So, I'll have a sort of the bag see what there is further to keep, and what else there may be to offer for sale. Ive still to shift those Marconi fill-guns, looks like the last person isnt interested anymore. Plus a Philips repeater and some met grade thermometers! The more I can sell the less Julie will complain at all my junk, and the less the show will cost me in antenna systems!

Well, ive the HF antenna mount on the car to test now. Im sure the bands are not as dead as that radio makes out, but the radio tests out fine. Dinner first I think though - frankfurters, onions, shrooms and scrambled egg, oh and a bit of red sauce.

Saturday, 6 July 2013

Marconi Cheesed

Bollocks! Thats the only word I can think to describe this. I went into the workshop this afternoon to show Sam the transverters receive chain working, switched on the Marconi 2955B and was greeted by a screen full of random ASCII characters. So, thats my one and only signal generator U/S. Ive found only one reference to a fault on these that causes the display to mess up, and that suggests the crystal oven 10MHz frequency standard has failed. Thats almost certainly an obsolete part. Its also mounted on the same board as the EHT circuits for the CRT, so im really not looking forward to trying to find a way of getting the scope on it.

But, until thats fixed, or I get another signal generator, im rather stumped on quite a few projects. 4m especially is not an easy band to try and work with off-air signals either.

Red Rose QRP festival tomorrow. I put a bit on the charity entrance fee auction, and ended up winning it! So ive already got my entrance fee and dinner paid for, albeit at a bit more than it would have cost on the door! Just need to take something tomorrow to prove it was me who won! Ive a small list of things to get, but generally just looking for a few bargains. Wonder if there will be a scrap 2955B...

Friday, 5 July 2013

Time out

Since the last posting on here, Ive been a bit off, plus had to work, so not got anything further done on any of the projects. So why the heck am I writing a post?

Red Rose QRP festival is on sunday. Now that Sam is back off his residential visit to Hadrians Wall, he says he'll come with me. I have a small list of things to look out for. Top of the list is a small audio isolation transformer to isolate the scanner audio output from the Marconi 2955's audio input. This should sort out the problems using it on the transverter test bed. A couple of nice ali boxes for the transverter and the WSPR transceiver are also on the list, as is a discone antenna for use as a test off-air source.

All the trimmer capacitors I ordered have arrived, so ive a good basic stock now. Some even came from the Netherlands. Hopefully I can pick up some older PMR kit to strip down soon. I also need to try and off-load the Philips repeater I have, no use to me at all and taking up a load of space. Wonder if there will be a free ebay listing weekend?

Worked a couple of special events on 20m on way home from work this morning, and got compliments on my audio. You can stick your Heil prosets - my mobile headset is a converted old Plantronics office telephone headset!

Sunday, 30 June 2013

Tranfixed by Transverter

Last night, after one of my quite regular bouts of total inability to sleep, hatred of the covers, and before the Nytol had chance to kick in, I decided to think back over the receive sensitivity problem. So, I sat and thunked. Suddenly, the folly of my argument hit me. If I have to have the capacitor fully meshed, then my resonant frequency is too high, and no amount of widening the inductor turns spacing will make it lower! What I need is more turns, or more capacitance.

Tonight then, once the boys were in bed, I slunked my way back out to the workbench. Having already put the new coil on, and having during the day found a few moments to build the LO Buffer and put the SBL-1 DBM in place, I decided to properly connect the IF and Antenna connectors, and to run the tests again with a view to seeing what needed to be done.

Well, tonight I had to put a stonking -67dBm signal on in order to even hear the received signal, let alone measure the SINAD. Very odd. Both AM and FM were the same, and couldnt hear a thing in SSB. So, in frustration i disconnected the audio out from the scanner - and bang, stonking loud received audio tone!. It seems the funny issue I had with the scanner must be some sort of ground problem due to it being on battery and all the rest of the kit being off the mains. Test set up works fine until I connect the audio lead from the scanner to the 2955, which kills the received audio.

So, doing an FM SINAD test by ear, I found a perfectly acceptable -117dBm for 12dB SINAD. With the test set in AM mode and the modulation off, the slight frequency reading error of the scanner allowed me to hear the high pitched difference tone down to -127dBm just discernable, thats a pretty decent 0.091uV!. The audio tone was perfectly obvious at -120dBm/0.27uV.

But, heres the real surprise! I adjusted the test set to zero beat the scanner, and then backed it off a little to give a strong to my ears 800Hz tone. This was at 70.401MHz on the test set, 28.400MHz on the scanner. I then peaked the input tuned circuit by squeezing the coil turns together a bit, and adjusting the trimmer. It peaked best signal with the cap just short of fully meshed. So, I started turning down the signal, and down, and down, until the test set wouldnt go any lower! At -135dBm the tone was still very readable, had it been CW it would have been reasonable if not easy copy. Thats 0.039uV! I even swapped to the BNC output on the test set, but all that happened is it got better! (which shows that my N to BNC adaptor needs cleaning). It was even obvious back in the house listening from the open kitchen door!

video

I have to say I am amazed. Such a simple circuit, just a tuned circuit and an NE602 IC, and its sensitivity is awesome, even when used with lets face it a pretty poor IF receiver. The video above shows the set-up and the circuit under test. The warble is the signal from the Marconi 2955 test set.

It does of course mean that I owe Roger an apology, as I suggested that perhaps there was a typo in his schematic, as the diagram says a 35pF trimmer in this circuit, but his photo shows that his transverter has a 65pF one. Mine has the 35pF. I will stand by however my ascertion that 35pF is too small. Mine is very close to fully meshed, I think with a 65pF it would be more like half meshed, which I think is preferable in this case, I dont like things to be at the limit. I probably wont change the trimmer though, but instead add a 27pF or so fixed cap in parallel. So Roger, if you happen to read this, my apology on record, but also my gratitude and admiration for an amazing circuit!

Strangely, when I tried to check the LO Buffer, I couldnt get a frequency reading on my counter, neither could I from the oscillator (which was quite clearly running properly!). This is probably an issue with the counter rather than anything else, something to look at another day now.

Saturday, 29 June 2013

CaPs LoCk

After the 12 or so hours of preparation yesterday at home and today at the village hall, the couple of hours of Toms birthday party were brilliant. On arriving home afterwards, there was a small packet awaiting my return, marked Saffron Electronics, residing within which were 10 65pF trimmers.

Eventually, I managed to slip out to the workbench for a short while. Much of my time was spent putting a small cable entry chassis mount BNC socket on the end of a bit of RG-174, and sticking F-connectors onto a length of RG-59. Those two jobs done, I added one of the new trimmers to the crystal already mounted on the 10m WSPR transceiver board. I can at least now start building the LO proper, and hopefully have it running on the 14MHz fundamental soon.



Being rather knackered, I didnt wish to work on the LO buffer amp on the 4m transverter tonight. I have a particular aversion to dual gate MOSFETs as they are rather expensive four legged fuses, and with my antistatic wristband being 'somewhere' in a box under the bench, decided best leave that task for when im a little more awake. Instead, I decided to rebuild the input coil on the 70MHz receive side. This is a 7t 4mm dia air wound coil, tapped 1t from ground. I had built the original from 18swg wire, very sturdy, but found its associated trimmer capacitor had to be fully meshed for best results. Hmmm, I much prefer it when I can peak a tuned circuit and tune out either side. Being so sturdy, I couldnt open the turns up to reduce the inductance a fraction, and hence increase the resonant frequency. So, a new coil was would with 22swg wire, still sturdy enough, but now more manipulable. I suspect this inability to adjust both coil and cap, and hence not be able to tune the pair up to a high enough frequency, was responsible for the -87dBm receive measurement. I also this evening, took the liberty of running a 12dB SINAD test on the MVT-7100 at 28.4MHz, and it came in at better than -122dBm, so it does look like the loss is in the converter stage.





The photo above shows the transverter so far. The new coil can be seen on the right above the antenna changeover relay. On the left, roughly in place but not yet soldered on, is the SBL-1 double balanced mixer. Being a hot carrier diode ring, this can work at a higher level than the NE602 Gilbert Cell mixer used in the receive chain, and will form the heart of the transmit up-converter. However, before it can be fitted, the MOSFET buffer amp needs to go just above it.

Before going any further on the transmit side, I think I will connect the nice new coax connectors and retest the receive.The bulkhead BNC sockets mean I wont have the mismatch of a pair of crock clips during the test as was the case last time. But for now, im turning in for a good kip.

Thursday, 27 June 2013

If its not one thing, Its yer mother

The Transverter is coming along, added the antenna changeover relay, ex- of an RC-690, and have started the 10m WSPR transceiver. When I say started, I mean ive soldered the crystal on, then come to a shuddering halt at the realisation ive no damn trimmer capacitors left in the right values. Not even anything I can bodge into the circuit.

So, ive had to order some. Bloody hell! Might as well be ordering a kilo of Columbian Gold! I really must find some junk with lots of trimmers in to strip, because the price of these things is getting extortionate.

So theres nothing more I can do on the WSPR side, until these arrive. I can do a bit more on the transverter though, although not much. Looks like i'll have to instead finish of some long overdue old projects.

4m Transverter - Receiver success

After a bit of lack-of-sleep brain addled cocking up, I have managed to get the coils for the receive side of the transverter wound properly. A quick, but not exactly accurate, test was set up, using the Marconi 2955 test set as signal generator on 70.4MHz, and the MVT-7100 scanner as the receiver, tuned 28.4MHz. With a source signal with 1kHz 45% AM, this little circuit worked nicely, giving a 12dB SINAD (roughly, by ear) of about -87dBm. With the modulation off, and the scanner in USB mode, a tone could be detected by ear with a signal of about -102dB. The set up was far from ideal, the input from the signal generator was connected with a croc-clip lead, and the scanner connected with an array of various adapters to connect to the TNC connector used to wire up the converter output. The scanner didnt even need tuning a couple of kHz away, as being a scanner its frequency resolution isnt great to start with. It was also a bit intermittent, did some odd changes when I touched the case. I suspect a proper test set up will be much better. I did notice that the trimmer capacitor in the receive circuit was best set at max, I may try a bigger value in here to see what effect it has, or maybe widen out the turns of the coil.



Onto the antenna and power switching arrangements now, which I want to have done before starting on the transmit side.

Before however, im going to pinch yet another of G3XBMs designs, and make a start on the 10m WSPR transceiver. I have the necessary toroids and crystals now, so first job is to make a rough draft layout, and then build and test the oscillator and doubler.

Wednesday, 26 June 2013

Old and New

Spent an almost pleasant couple of hours salvaging components from junk equipment this morning. Mostly the usual suspects - electrolytics, small transistors etc, but since the big beast im dismantling is an old analogue TV transmitter, theres some real nice RF components as well coming out, one board has a lot of small ferrite binocular cores, and several nice Toko coils. Sadly, most of the really nice parts are very well soldered to the groundplane, through hole plated, and surrounded by masses of SMT parts. I really think I need a bigger rated soldering iron for taking these off. I did try with the heat gun, but its not precise enough and just torches the boards.

Whilst out doing this, I missed the post lady, and one coming back into the house found that a much sought after parcel from Graham G3MFJ had arrived - G-QRP club parts! A sexy collection of toroids and Spectrum coils (modern Toko 10K), some needed semiconductors, and of course - the crystals! I can now not only carry on with the 4m transverter, but can start the WSPR 10m transceiver as well!

The only parts im desperate for, sadly Graham doesnt stock - trimmer capacitors!

Oh well, still a few in the junk boxes, and theres a rally in the not too distant future...

Off now to cook up some Frankfurters, shrooms, onions and cheese. Mmmmmm

Friday, 21 June 2013

Tub Thumping

Butter tubs, that is. Dozens of them, mostly 500g, the occasional 1kg, and a couple of ice cream tubs.

Why? I'm adding to my component storage. I use butter tubs, in particular Sainsburys or Flora, because they stack well and are quite strong.  It makes separating different component types easier, and keeps them tidy. Which is something I really need to do better! Containers added to my shelves now for toroid cores and ferrite beads, trimmer capacitors, coil formers (ive included Toko/Spectrum 10Z and S18s in there), battery holders, relays, plus some others.

Its quite amazing just what a huge variety of different components there are. Its easy to lump, say, small signal transistors into one box, but thats still awkward - what about bipolar/FET? general purpose/RF? All I can say is I need a lot of butter tubs!

Anyway, enough about my storage difficulties. Some RF parts on order from G-QRP club sales today, mostly for the 4m transverter, but some to make a start on a 10m WSPR beacon transceiver. Just realised though, that if I decide to follow Roger G3XBMs design, im going to need half a dozen T37-6 toroids. I have T50-6 and T50-2, and could have ordered the 37's today, if i'd bothered to check the schematic! At least I have the crystals ordered!


Ive also had an idea regarding the secondary antenna for the show. I had planned some form of vertical array, but im wondering now if a cobweb might be the answer? It will go on the 5.4m mast, so not sure if the height is good enough.

Wednesday, 19 June 2013

Clock On!

After repairing the broken former, regluing pads that came loose during experimenting, and discovering the Spec An is 4MHz off, the local Oscillator for the transverter is now running where it should be - 42Mhz.

Despite being fairly certain the series inductor is the same type as specified, and after removing several turns to get it to 10t, it still wouldn't oscillate correctly. I then took it down to 5t and was wayyy over! So, a deft rewind, followed again by stripping off one turn at a time and testing, plus the expedient of changing over to the Frequency Counter from the Spec An, led to the discovery that free running around 42MHz needs 7t on this former. Adjusted to within a few hundred Hz, and took the shorting link out -Bang on!

Next step, then, is to build the Receive Down Converter. This is a simple NE602 circuit. The only down side here, is that other than feeding the Signal generator into it, I have no horizontal antenna for 4m with which to try and receive an off-air signal.  I feel a halo or dipole coming on...

I still need to verify the instrument readings against listening for the oscillator on a GCR.

4m Transverter

The Larkspur mast is nearly refurbished, just one section left to repaint, so ive turned my attention to another project - a transverter for 4m. This is the G3XBM QRP design.

Its taken me quite some time to even get started with this, as the 42MHz crystals are not exactly cheap nor easy to come by. And once I had the crystal, I found I didnt have the series inductor. However, a kind chap at the vintage forum has supplied said part, and so on we go.

Working with 'Manhattan' construction, I have the Local Oscillator constructed. As is often the case, first time out it failed, and in my tired state trying to fault find last night at gone 23:00, I confused myself with the display on the spectrum analyser, and so the one time I did get it to oscillate, I thought it was just a false reading.

Having correctly started alignment this morning, I find it free runs at 27MHz. A quick check of the inductor shows it has far too many turns on than specified, so next task is to take a few off and get it free running around 42MHz, then the short can be taken off of the crystal.

Just started removing the excess turns, and have cracked the damn former off the base! Out with the cyanoacrylates...


Friday, 3 May 2013

Morse

OK, lets be honest about this. I love Morse, but i'm crap at it. Which is annoying, as I seem to have developed an interest in collecting telegraph keys! I now have a Kent solid brass straight key, a WT8 AMP No.2 Mk III, and a pair of 'leg' keys - a McMurdo and a Racal, both miniature keys designed to be strapped to the operators leg!

I also want desperately to use Morse on air, comfortably. Ideally I want to use it to make at least some of the contacts during the Doncaster Show. CW on 40m might save us from the death knell of the National Field Day contest. I'm sure I can get a CW operator if needed, but I really want to do it myself. Besides, CW is ideal for my home situation - using Morse and 'phones would mean I could operate more at night.

I'm back learning the morse. 10-30min a day. Ive moved onto common words, as lets face it I know the damn characters, and random code is so dull. My numbers could do with some improvement, and I certainly need to work more on punctuation and prosigns. Ive decided that 18wpm is a realistic target speed, so im training with the actual character speed at 25wpm (so Its easier not to count the dits and dahs) and the code speed at 18wpm. If I make decent progress I might go to 25wpm code.

The Larkspur mast is coming on well. Only two tubes need doing now, and one has already been sanded down. All the others have been painted, NATO matt green. Most of the locking collars are half painted, the other side i'll do once they've had time to dry. I would have had them all in that state today, but my primer ran out of propellant, so one is still awaiting priming.

Finding the guy pegs and a spanner is proving harder though!

I really must organise a site visit for the show. I need to know the area in which the antennas must fit, and four months will fly by if im not watching closely!

Im still trying to get a 42MHz crystal so I can start the 4m transverter project. Again one is up on ebay. Im sure the seller is Shill bidding but hes the only one so im going to have to grin and bear it and bid.

Ive abandoned the Pixie 2+, and will strip it for bits. Just couldnt get it to work. Im going instead to build a project from DeMaws 'QRP notebook' possibly a gutless wonder for 40m

Monday, 22 April 2013

Plugs and sockets

One task I have to complete, which at face value should be simple, is to add a connector to my Time Lapse controller for my SLR. Unfortunately, when I first set up the controller system, my camera was a Minolta Dynax 404si, a film 35mm SLR, and it only took a remote release, or a simple timer controller. I now have a Sony SLT, which although it takes all my Minolta accessories, also takes a digital time lapes intervalometer. It is to this I need to add a connector, but sadly, the connectors I used were extremely expensive and rare Lemo miniature multipole locking connectors. I have none of these left spare, and in the very few places in the world I can find them for sale, they cost upwards of £40 each.

So, I have to embark on the process of replacing the connectors across the whole system, with something much cheaper and more readily available. Luckily, there is such a connector system, one which I already make good use of - 3.5mm audio jacks. The camera system uses three connections - focus, release, and ground. So stereo connectors are ideal. I also have a need for a custom lead from my gear lever mounted PTT control to the microphone interface box on my rig in the car, which uses 3.5mm jacks. So, I have a batch of connectors on order to allow me to complete these tasks.

My run of night shifts is now complete, so after a decent sleep and a few bevvies, I can finally get back to work on the various projects that require my attention. I should be well on the way to having a completely overhauled No. 1 mast soon.

As I type this, G4FONs Koch trainer software, is sending me random Morse characters at 12wpm (character speed 20wpm). This time, I really want to crack it. I want to start using CW in anger, and would love to be able to use if on GB2LDS. Which reminds me, I must get the license application sent!

Thursday, 18 April 2013

Show Antenna Designs

The paint for the Larkspur mast arrived yesterday. Theres still plenty of work to be done on it, but now I can get one with more than one task at a time!

The Doncaster Show will also need an antenna that will give us access to the WARC bands. Ive decided on a vertical system for this. I was intending to make something that would work on the fishing pole mast, but have decided instead on a Fan Vertical design that will utilise the 5.4m Clansman mast, there are several good reasons for this -

1. The 5.4m mast is much sturdier and will withstand the wind loading of the extra antenna wires better
2. It is already designed to be used as a vertical and has suitable fixings for the 20m element to run up the mast
3. I have spare mast sections that can be used to form a sturdy horizontal cross member support for the other four bands antenna elements
4. It will also be capable of supporting a VHF lightweight antenna at the top
5. Its guying radius is 3m, add on a 2m safety zone, and you have 5m. The required ground radials are to be 5m 30cm. A bit extra safety margin and its all contained.

My worry is being able to fit the 40m inverted V dipole into the antenna field, and having sufficient coax available if the shack has to be a distance from the antennas.

Ive also taken a punt, for a few quid, on a little digital voice recorder unit. The reason for this, is i'd like to do more CQ calls while mobile, but find it a bit tedious! If this sounds decent, and I can suitably modify it to feed into the mic audio and PTT system of the FT-857D, then it should just be a touch of a button to put out a CQ. I know its just a promotional toy, but it is from Cisco, so with any luck its half decent audio.

Tuesday, 16 April 2013

No. 1 Mast overhaul and refirb

As complex as this mast first seemed, its really quite easy to work on. It does of course help to have the field repair guide, which shows the correct method of dismantling.  Due to some rather over zealous repainting done sometime in the past, theres quite a bit more to be done than just clean it out.

First stage then is to dismantle and clean out the crud from about half a decade of neglect. To start with, the F adaptor needs to be removed. This is soldered into the top pole, and needed a bit of brute force and a blowlamp. Once this was out, the base assembly could be taken out. This is only screwed in, but needs a good whack to break the pein over the seam. This assembly was dismantled, degreased and cleaned, given a rust treatment with Jenolite, and then rebuilt with a generous coating of lithium grease.


With the base and F adaptor taken care of, it was time to take a look at the poles. These have to be extracted from the base, with great care taken at the top end to collect the locking roller. These are what works with the cam cut into the locking collars to hold the mast together when erected. Each is a slightly different diameter so has to be kept with its associated collar. As can be seen from the photo, the poles need a good rubbing down and repainting. They are steel with a copper plating, so more care needed when dealing with the worst of the corrosion not to strip off the copper plating.


The first four locking rings are shown removed below. One is missing its lug, which is needed to give purchase to a seized ring. All of them need a complete repaint, it looks like they were last repainted with an emulsion brush! The rollers are inside each ring in the photo.


The top pole was the first to be stripped and primed. Each pole is getting this treatment, although some are not as bad as others and will not be stripped back as far. None are down to bare metal as this isnt required. The photo shows the lower two sections awaiting being taken apart, and the top section after priming. The end shown has a large area of unpainted metal, as this is the area that makes physical contact with the next section and the locking collar and roller. The amount of bare metal isnt obvious in the photo because of the masking tape around it.


The guying rings also needed a complete repaint. These were stripped using an abrasive wheel down to bare metal to ensure the nicks and scratches were rust free, then primed.

To date, three pole sections have been stripped/rubbed down, and primed, as have the two guying rings. Four of the locking collars have been stripped, two are still in the process and undergoing degreasing. One has been primed ready for respraying. The base assembly external parts have also been primed. This will get a coating of VHT matt black rather than the matt NATO green the rest of the mast will be resprayed in. The paint should be on its way now.

Originally these masts were in olive drab, and gloss. I have a personal preference to not use gloss, perhaps that stems from the matt paints we used on the Landys in the squadron. Either way I prefer military kit not to be reflective!

Im still in the process of trying to find the correct guy pegs for this mast, and the specialist spanner and the base insulator. But, its still some time until september, when I need this mast to be deployable, so hopefully something will turn up in the meantime.

Also needed for the Show, is another vertical antenna that will provide our frequency agile station. Im once again looking at a 5-band fan vertical for this job, but need to work out how to make stable spreaders that will work on the fibreglass fishing pole mast. (or the 5.4m clansman)

Sunday, 17 March 2013

Antennas for show

Time has come to start thinking about the show - The 2nd Lions Doncaster Show. If at all possible we want a dual HF set-up this year, one on 40m fixed, and another to be 'frequency agile' to help get around the NFD contest. Im very much disinclined to bother with 2m FM this year, unless I can secure a couple of day operators extra. If we do have 2m, then a lightweight antenna is needed, the 1/2w commercial being too heavy.

We have a new (to us) 27ft mast - an ex-army Larkspur telescopic. This will hopefully provide the main HF antenna, using the Clansman antenna wires, in an inverted V. Im missing the three guy pegs at present but im sure those can be found before september.

Since im looking into antennas for the show, and since im also looking to rig something up for the VHF marine band, my thoughts have turned again to the fibreglass parts and mountings of an old colinear I have. After looking at various ideas, we come back, as always, to the Slim-Jim. Nothing special, the Slim-Jim, but remarkably easy to build. Trouble is, although I have plenty of 450 ohm window line, this is too wide to fit in the fibreglass tube of the old colinear. I could bend it over a little, securing it in its new shape with cable ties, which will allow it to fit but of course change the characteristic impedance.

Another idea, is to build a slim jim from the huge amount of high current twin cable I have. This has a spacing of about 3mm! I might give one a try and see if it can be done.