Wednesday, 15 November 2017

Software Defined Radio and Pager Decoding

Ive been playing again recently with my cheap R820T RTL dongles. These, when used with suitable custom drivers and SDR software, are interesting devices allowing for the reception of all manner of signals.

In this case, ive been using mine with the SDRsharp software package to control them (referred to as SDR#), and playing with attempts to receive and decode digital audio and trunked network signals. Ive not had much luck that way yet, but what I have had success with are pager signals.

Some of you reading this (I suspect most of my readers!) will be old enough to remember the period in the mid 1980s to the early 90s when mobile phones were the size of a housebrick, public payphones either vandalised or used as conveniences, and the alternative to a landline the very short lived Rabbit DECT system!

During this telecommunications chaos, those who wished to look like Yuppies but without the budget for a phone, carried a pager. My mate Ian had one - I dont actually recall it ever beeping! ;-) Most people think these legacy devices are obsolete with the coming of GSM phones, but no, they still exist, now used mostly for alerting on-call staff, sending telemetry messages, and are also now a valuable part of the emergency services response systems.

These devices live on the VHF bands around 138MHz and 153MHz. Two protocols are still in general use - POCSAG (Post Office Code Standards Advisory Group) and FLEX, at several baud rates from 512 and 1200 (POCSAG) to 1600 and 3200 (FLEX)

By combining SDR# with a software package called PDW, these signals can be decoded into their numeric or alphanumeric messages.

There are many users of these systems, and it seems different channels carry generally different traffic. The frequency in use in the image above is 153.275MHz. This is a 1200bd POCSAG signal, with timing/test messages (not decodable) every minute. When there is message traffic, it is generally numeric or simple tone alerting. Likewise its apparent sister frequency 153.250MHz. To the right in the waterfall can be seen 153.325MHz (3600bd FLEX) which seems to carry a lot of machinery telemetry and general 'call so and so' messages, and 153.350MHz, 1200bd POCSAG (CH3), which for me is the easiest and generally busiest frequency. To the left of the waterfall can be seen another FLEX channel, 153.025MHz, this also transmits a very regular timing pulse, as can be seen.

For anyone trying the above software combination, I have found that the following settings work for me - RTL gain 38dB (adjust this on yours to get signal peaks around 30dB above the noise), receiver bandwidth 15kHz, SDR# audio out 54dB.

I have spent quite some time exploring the 153MHz channels, so now will move down to 138MHz and try my hand at decoding those.

On a related note, ive taken the plunge today and purchased a Uniden UBC-125xlt handheld scanner. This isnt to replace my venerable Yupiteru MVT-7100, but instead to add to my capabilities with its 'close call' features. Ive also ordered another R820T2 SDR dongle, and a pair of MCX to BNC pigtail cables, as I intend enclosing the dongles into aluminium boxes to help cut down the noise floor.

Tuesday, 7 November 2017

A Plug for Bulb...

My energy supplier (electricity and gas) is Bulb Ltd. They run a referral program for new customers.
The link below ive provided for anyone who is considering switching energy suppliers, to take a look and do your own research into them. Take a look at their reviews online as well.

So, your thinking, all well and good, but how does that help your readers save money?

Well, its simple - If you sign up to change your supplier to them, using a link that I will provide below, they give you a £50 initial credit! And, whats even better - they give me one as well!

Heres the link -

Numbers Stations

Many years ago, at the height of the Cold War (mid 1980s - not the mid '60s as the press would have it!) , I used to listen to strange broadcasts consisting of spoken groups of numbers. Much later I discovered these 'numbers' stations, existed all over the world, and were government run covert stations, transmitting operational orders to 'agents in place', what the thriller writers would call spies.

Since the fall of the Berlin Wall, these stations have much decreased in number and activity - but they do still exist!

This morning, I have been listening to one named E11 (these names come from the CONET project, that documented these stations), on 7317kHz USB.

The original Enigma and CONET projects no longer exist, however there is still a group that is documenting these stations -

One great aspect of this projects website, is that on the homepage there is a schedule and a 'next station' timer! This makes tuning these stations in very easy - simply tune to the frequency and mode shown for the 'next station' and wait...

Sunday, 15 October 2017

All the UKs frequencies on Google Earth?

Yesterday, someone pointed out to me that it was possible to download the whole of Ofcoms license allocation database, as a comma separated variable delimited file. This is the list of who holds what licenses for what specific frequencies, not amateur licenses, or users of license free channels.

This info of course is of great interest to scanner users, but the original .csv file rocks up at over 70MB and around a third of a million entries!

Now, wouldnt such a file, showing who is using what frequencies and where, be great on Google Earth?

Glutton for punishment that I am, and recognized at work as the Google Earth Gnome, I foolishly set about trying to convert a 70MB .csv file into a workable set of .kmz files!

Key to this, are three steps - First, remove all non-geographical entries. These are frequencies and users allocated on a nationwide basis, and hence have no position information for Google Earth to work with. Second, remove all duplicates. In this case, a duplicate entry is one where the same user, is listed with the same frequency, in the same location. A frequency can be used by the same user in a different location, thats a valid entry, as is a different user using the same frequency, etc. And third, split the file into manageable chunks.

The first two operations have been done using the data handling tools in Microsoft Excel. The third needed some thinking about. I opted to split the file into separate files based on area, and chose to use the Ordnance Survey 100km gridsquares

Most areas, this creates an easily handled file size. The exception is grid TQ, which covers that there London. The density of allocations in London is such that I have had to split that file into four, and perhaps even more, based on frequency band.

The resulting .csv files, can be imported direct into Google Earth. Ultimately, I wish to convert them to .kmz files that are native to Google Earth and can be distributed, such that any user can just open the file and it will work. Imported .csv files require some setting up.

The above pic is a screenshot of my Google Earth Pro with three of the gridsquare files imported and enabled.

Tuesday, 10 October 2017

Can my blog save you money?

Quite possibly!

Just recently, I received an email from British Gas, my energy supplier at the time. This email informed me that my gas and electricity bills were not only going to go up by a extortionate amount, but also that they were ending the dual fuel discount as well. The general gist of the email was "pay up or sod off"...

... so I sodded off!

After a lot of research, trawling comparison sites and the like, I narrowed down a number of new suppliers, which were smaller, much cheaper, and it seemed more ethical than British Gas. And out of these, one caught my eye - Bulb.

Bit of a gimmicky name for an electricity supplier! But, the more I read, the more I liked what I was reading. Committed to customer service, committed to renewable energy sources, and online open forum for customers and non-customers alike. So, after looking at my potential savings, I signed up with them.

The link below ive provided for anyone who is considering switching suppliers, to take a look and do your own research into them. Take a look at their reviews online as well.

This was just over a month ago, and ive just submitted my second set of meter readings. All seems to be going very well so far, and any queries ive had have been dealt with by their team via the forums swiftly. So far im happy with them and alls going well. Im on a list for the trial of next generation smart meters as well. The only odd part is that payments are done initially by debit card, but you can call and set up a direct debit (I must remember to do this!), and also, they work on an advance payment system, which means you actually pay up front, and if you overpay either it holds on your account or you can ask for it rebated. This seems very odd at first, but in many ways it does make sense.

So, your thinking, all well and good, but how does that help your readers save money?

Well, its simple - If you sign up to change your supplier to them, using a link that I will provide below, they give you a £50 initial credit! And, whats even better - they give me one as well!

Heres the link -

I would suggest this - If your considering changing your energy supplier - go and research Bulb online, also research other suppliers, and find the one that is right for you. IF, you find that Bulb suits you, then use my link above to get yourself, and me, fifty quid!

Im not going to try to convince you, coerce you, or force you! But, it makes sense to me to take up an offer if your switching anyway, so my referral link is there above for you, should you choose to use it.

Clear as mud

Well, for some reason, the plum wine isnt clearing. Wine making has taken up pretty much most of my spare time recently, and shortly some beer brewing will also join my activities, now I have a nice big fermentation bucket!

Thats not to say there is no radio planned! Due to workload, and my walking mate Bob M1BBVs change of career, walking and field radio have been rather sparse. However, hopefully soon (next few weeks) we will be back out there. A few rail trail walks and some long outstanding SOTA is on the horizon!

Anyway, back to the wine! It would seem the problem here is a protein or pectin haze. As this wine has already has two-part finings (isinglas/gelatine and keiselsol) ive decided to try another electropositive fining agent,  this time Bentonite, which is known for its ability to drag proteins out of suspension. Its a bit more faffy to use than other finings, as the extremely hygroscopic particles of this volcanic clay must be hydrated into a slurry prior to use.

But, it does also give me a chance to exchange the airlock and bung fitted, with a solid bung, freeing up the airlock for other use. Hopefully now this wine will clear over the next couple of days, and can then be bottled - which will free up the demijohn for racking off one of the other wines!

Monday, 2 October 2017

Variant "WOW" wine

Ive not been on here much lately, mostly due to work and the like, but that doesnt mean ive not been busy,

I have, just not with radio!

Instead, Ive been wine making. This is something I always intended to to do, but never got around to, despite my experiences of it as a kid helping the chap over the road.

But it occurs to me that my blogs are a good place to record experiments in this line. To date ive completed and drunk a 5L kit Cabernet Sauvignon, I have an apple wine, using my own fruit, bottled. A plum, again using my home grown fruit, in the process of clearing. I have a kit chardonnay bubbling away in early secondary, and a strawberry getting close to the end of fermentation.

This morning, I decided to quickly throw on a "WOW" variant. Now, WOW stands for Wurzels Orange Wine, and in its pure form of course uses oranges. A 'variant' generally refers to a wine made using store bought juices. This is what I have gone for.

This will be an Apple, Watermelon and Raspberry wine. No messing about with hydrometers for this one! Just 3L of 100% juice and 1100g total sugars.

Heres the recipe -

1L 100% red grape juice
2L 100% apple, watermelon and raspberry juice*
820g granulated sugar
1L water
1 cup strong tea (tannin)
1/2 tsp Pectolase
1 tsp glycerine
2 tbsp lemon juice (acid)

*1L in must, 1L in fridge for topping up

A general purpose wine yeast, activated in a  cup of warm water with 2 tsp sugar, was the first thing to get started. After that, the demijohn, airlock and other needed kit was sterilized. Luckily these days, with everyone so health conscious, cartons of juice have the sugar content printed on them. So, I knew I had 308g of sugars in the juice, so needed to add around 808g. With the variability of scales, I probably put 820g in. I didnt mix the sugar well enough with the 1L extra water, so have just had to spend 5mins swirling the must to dissolve the excess. With all the additives, sugar, water and first two juices in, theres a bit over 3L of must, coming to just below the shoulder of the demijohn. The lemon juice provides the acidity, whilst the strong cup of tea provides the tannins. A bit of glycerine to improve mouth feel, and some pectolase enzyme to help break down any fruit pectins.

I pitched the yeast once everything else was in, and when checked this afternoon (about 6 hours later) it was bubbling at about four every minute. So, after getting all the extra sugar dissolved, ive now transferred the demijohn to my usual 'production line', where it can now stand and crack on with primary fermentation. As WOW wines can often become somewhat 'lively', this one is stood in a drip tray!

Once its done with primary, maybe three days or so once it gets properly started, i'll top it up with the remaining juice. This wine should complete secondary in under two weeks, and once cleared should be drinkable more or less straight away.

Saturday, 29 July 2017

New Mode Time - MSK144, and Random MS

With propagation down, and the weather rather hit and miss, I thought i'd try my hand at something new.

To make things difficult for myself, I picked a little known datamode protocol - MSK144, and an underused band for which I have only a low, fixed azimuth beam - 6m.

And to ensure I really did have the hardest time possible, this mode is used for a difficult propagation path - Metero Scatter!

The principle behind meteor scatter is fairly straightforward. Everyday, thousands of minute particles of space dust, usually no larger than a grain of sand, collide with the earths atmosphere, and are burnt up by the protective layers above us. Those grains, while out in space, are Meteoroids. As they pass through the atmosphere and burn up, they become Meteors. Should any part of it survive its encounter and reach the earths surface (which would need to have been a rather big bit of rock!) the remains are Meteorites. On any clear night from a suitably dark location, you can see a few random meteors. Those of you of a Disney fairytale princess persuasion may wish upon these shooting, or 'falling' stars - those with a hundred watts or more of throbbing RF and suitable software can make contact over them!

As the meteor burns up, it leaves behind it a trail of ionized particles. It is against this trail, a fleeting moment lasting from a few tenths of a second to a handful of seconds for a big, pebble sized meteor (which visually would produce a fireball or 'bollide') that we fling our radio messages, hoping to scatter enough signal from the trail to reach our partner station.

At certain times of the year though, the earth passes through streams of dust left behind by the passage of comets through the solar system. At these times, there is a marked increase in the number of meteors, and these are known as Meteor Showers. As with any event that affects propagation, these bring the latent operators out of the woodwork. However, the next shower, the Perseids, is several weeks away.

At times like this, you either set up a 'sked' with a particular station, or call CQ to try and make a random QSO...

As you can imagine, A random MS QSO is hard work! Your facing a combination of limited beamwidth (the same trouble that we have photographing meteors - your limited lens field of view means the meteor you see with your eyes is usually not in the cameras view!), rare and fleeting propagation, and few, if sometimes indeed any, other stations using the same mode and same frequency.

But, there are ways around! And thanks to the internet and fast CPUs, its a bit easier! We can announce on dedicated chat forums that we are calling, there are strict rules and message formats, and there are modulation protocols that run fast messages to increase the chance of a usable reflection. In the old days, MS was done by high speed morse! Now, its done using fast data modes such as MSK144, JT6M and FSK441.

But, despite all that, a random MS QSO is still a challenge! To state how much of a challenge, well, Ive probably spent 50h on it in the past few days, transmitting for maybe 2h total key-down time, and ive made two contacts!

The screenshot above shows a meteor 'ping'. The two halves of the window are 15 seconds long, and my transmit slot was 15 seconds between them. In 30 seconds then, only a single brief meteor passed at the right altitude, and position, between my station and that of Jurgen DK4AN. But, it was enough!

Sometime in the previous five minutes or so, a meteor had also passed that point, during one of my 15s Tx slots. Its decaying trail lasted long enough to reflect enough of my MSK144 message to Jurgen. The meteor in the image above, reflected his reply!

The software Im using is Joe Taylor W1JT's WSJT-X v.1.7. Joe is the chap who brought us WSPR plus a host of other modes for weak signal or fleeting propagation use - JT65, WSPR, JT9, JT6M etc etc. A new mode from him FT8, is rapidly gaining popularity! My antenna in this case is a 3 el yagi for 6m at the low height of about 15ft, fixed in direction to 120 degrees (roughly SE), the radio my Alinco DX-70TH running 100W. I am also using the VHF/UHF chat room of ON4KST online, in order to help co-ordinate my effort with others!

Around five minutes later, the above meteor 'burst' occurred. This was probably a slightly bigger grain of dust, maybe about the size of a bit of gravel, and it seems to have burnt up in pulses, a bit like when you see a naked eye meteor that seems to blaze up a couple of times. During this burst, I copied DK4AN again, decoding his message a couple of times. Now, as you can see, the messages are very short and direct. No data is wasted. The format is strictly controlled to ensure the right messages are sent and theres no confusion. As it happens, the WSJT-X program allows you to select 'Auto Seq' which means once you choose to reply to a signal, the computer can do the rest!

This last screenshot shows the completed QSO. Over a period of about 15 minutes, enough meteors were in the right place at the right time to allow their fiery destruction to do good and reflect our messages. A final confirmation via the online chat once the QSO was complete was made, to say thanks to Jurgen for his patience.

So, if you've always thought that meteor scatter was a mode for those with 'big gun' money for huge antennas, expensive low noise GaAsFET preamps, big linear amps and costly dedicated reel to reel high speed morse tape recorders, think again, and perhaps give it a try. If your in an IO or JO square, send in the 2nd slot! (convention - South and East sending in 2nd slot, North and West sending 1st). You only need a modest station, and a lot of patience!

Wednesday, 12 July 2017

'Scope repaired, and some fun with the Rectum Paralyzer

After some time spent blasting every moving contact in sight with Servisol, and resoldering any connection that didnt look pin sharp, my Hitachi V-212 20MHz Dual Trace Oscilloscope is now back working how it should be.

Inside the scope is very tidy, but clearly many years of grime had built up on the controls, causing all manner of irregular operation. Since I had to remove many of the plugs, these were all numbered with a Sharpie type pen so I knew where to put them back!

These two photos might seem pointless - actually, they are visual references as to where the correct control knobs and nuts were to be refitted! I also found that the protective film was never removed from the front panel, and was now in a poor state, Removing the film has brought the front panel back to near new looking condition!

After putting the scope back together, and replacing all the test gear on the bench where it should be, I started to have a play with the Spectrum Analyzer. (the weight of my analyzer is why it gets the name in the title! If your not careful with your manual handling these things can give you some interesting ruptures). I had heard that it was possible to get demodulated audio out, but wasnt sure how. Several youtube videos 'almost' helped, except that the described outputs were not as described on my instrument!

I sent a post in to G-QRP forum for assistance, but in the meantime, Sam came home from school, so I commandeered him for a few minutes to swap BNC connections around on the back of the analyzer, whilst I looked at what was on them on the 'scope. My connections are marked X, Y, and Z. One of these, Z I think it was, was tried first, resulting in a pulsing DC level. Clearly not that then. X was next up and showed a large triangle wave with a long 0v period, clearly the timebase! So the final Y connection was tried - yes! The 'scope trace showed just what the zero-span display of the analyzer did. Swapping the connection from the 'scope to the audio input of the 2955B, we had demodulated audio out of the test sets loudspeaker.

Using the 2955B isnt really convenient for this though, so I found a general purpose AF amp, based on an LM386, that was kicking about the bench, and connected that up. Perfect. I now need to find a box to put the audio amp in, so I can connect it neatly to the spectrum analyzer Y output for monitoring.

I hope eventually to us it for narrowing down airband transmissions, but im not accurate nor fast enough on the analyzers controls yet to pinpoint a transmission!

Car Stereo fault - Beat 485 repair

Well, marvelous isnt it? The Marconi 2955B goes on the blink, but before I can fix it the oscilloscope requires an overhaul. Get the 'scope dismantled for cleaning, lubricating and repair, and the flipping 2955B decides to start working again, leaving me with no idea whether something ive done, like reseating the cards, has fixed it, or whether the fault is indeed temperature dependent and likely to be a real twat to narrow down,

And while all this is going on, to really piss me off, the volume control on my car stereo fails! It randomly decides whether to go up or down whichever way I turn the knob!

I have a cheap after market DAB stereo, a Beat 485. This does DAB and DAB+ (why I bought it!) plus CD, USB etc. The volume control is not a traditional potentiometer, but a rotary encoder.

No photos for this fix im afraid! But it really doesnt need any, if your capable of doing this repair then you dont need a pictorial guide!

Opening the head fascia unit up is fairly simple - four screws and case clips, easily separated using a finger nail or similar thin object. The encoder turns out to be a mechanical type. This was to be expected as optical units are far more expensive. It also is a type with a central push button action (which I didnt know about its function on the stereo - turns out it selects the tone and balance options).

Once inside the head unit, the next job was to remove the encoder. This isnt particularly easy - there is a sizeable metal casing to it soldered down at either side, plus the five switch contacts (three one side, two the other). Ideally use a good hot iron here with plenty of heat capacity! I just plodded on with the 18W Antex, but the 45W iron would have been more sensible! Once desoldered, there are four folded tags on the underside that have to be lifted to dismantle the device.

Inside, the main encoder track could be seen, with two sliding contacts either side of the shaft. The pattern of the track could barely be seen it was so dirty! A blast with Servisol and a good scrub with a brush had it clean and shiny again. A gentle push with the end of a terminal driver reset the sliding contacts.

Reassembly was just the reverse of the above, ensuring of course that everything stayed in alignment, and then giving the securing tabs a good push down. After cleaning up the terminals, resoldering the encoder to the board was simple, as was rebuilding the head unit. I removed any other muck and dust at the same time.

A quick test back in the car shows that I now have a properly functioning volume control again!

Thursday, 6 July 2017

And now the Marconi 2955B is on the blink again!

Well, this just about takes the biscuit!

Not only do I discover that my understanding of the use of my spectrum analyser is probably woefully inadequate, and that my oscilloscope is playing up and needs a service, but now my 2955B test set is on the fritz! Again!

This time, I know im at serious risk of screwing the firmware if I dont fix it. So, its time to open her up.

The 10MHz Oven Compensated Crystal Controlled Oscillator (OXCO) unit, is mounted, horrifyingly, on the same board that generates the EHT for the CRT!

Rear of the Reference/EHT board
I very much dislike playing near EHT supplies! I know from experience what a belt from the anode cap of a brand new never been connected TV tube feels like - and dont fancy experiencing the same from an actual supply! So I very carefully ensured (with a pair of long nose pliers) that the reservoir capacitors were properly discharged!

Inside the Marconi 2955B. Note the warnings!
The actual OXCO's six pins desoldered very easily, and the whole module came out smoothly. I opened it up to see if there was anything obviously wrong inside

The 10MHz OXCO... bloody complicated inside!
But other than the trimmer capacitor (which I seem to remember being told could be the problem) it all looks ok, albeit extremely complex! So, I connected it up on the bench. 12v at 120mA steady (450mA initial) for the heater, 5v via a 22ohm current limit for the oscillator. 

On the bench...
 And the damn thing seems to be working perfectly!

...and seemingly working perfectly!
 I have had it powered now for about an hour. Ive even abused it - heating it with a hot air gun until it was too hot to touch, whereby it crept up to 10.00015MHz, and freezing it until the heater current maxed out again, and it barely dropped below 9.99998MHz!

Im now at a loss, but my suspicions center around either a power supply fault, or something as insidious  as a dry joint or leakage due to old flux! Where I go from here, im not sure, and ive a ton of work piling up that requires a working test set!

Spectrum Analysis - Am I doing it Wrong?

After a lot of puzzling and pondering over the transverter, ive started to come to a slow realization that much of the problem might actually be with me!

What I mean is, im starting to think that my knowledge of how to correctly read the spectrum analyser, and hence my interpretation of the results of tests on the transverter, may be lacking in understanding.

Sadly, when I try and find tutorials online, they are either far too in depth, such as guides to measuring phase noise, or based on much more modern and advanced LCD FFT instruments, rather than the 'classical' CRT superhet instrument I have.

So I guess what I need to do is get to very thorough grip with my SA instrument and its operation, before I progress with the transverter.

Tuesday, 4 July 2017

FARS Rally - Sunday 23rd July

A quick and blatant plug for this exceptional radio rally!

The Finningley Amateur Radio Society rally is fast approaching!

Located at the club HQ near Sandtoft, this rally is one of the best component and 'junk' sales around! I myself, with Bob M1BBV, will have a stall again this year, where I hope to be able to sell on some interesting items, big on our stall this year will be batteries for the Clansman PRC-349 radios (12v in a handy sized screw in pack), 'covert' diplexers, 'Panorama' professional antenna mounts, and Kenwood TK-349 PMR handhelds. Plus all manner of other junk!

I only hope to make enough money to cover my stall fees and the cost of whatever junk I buy!!!

More Transverter Trouble

Coming back to the 4m transverter after a short while doing other things, I found the bias current still unstable! So, I bit the bullet and added a 10ohm emitter resistor with a 1nF bypass. I can now get either an immediately stable standing current, or, it quickly (a few seconds) reduces down from around 40mA to a suitable 20mA as the diode stabilizes the bias.

Me, My Boys, Beer, Camping, and Radio

After a bit of playing around with Clansman radio in the garden, I moved on to build the PA section of the transverter. This involves the use of my one and only MRF237 RF power transistor... and it didnt go well!

First go at the 1W PA

 In the above photo,  the PA is built, and the transistor heatsink attached. On switching on - the PSU pegged the current limit!!!

Oh heck, not good! Lots of things were tried, resulting ultimately in nothing being connected to the transistor other than the collector to the tank coil and the emitter to ground - and it still pegged the PSU! Yet the transistor tested out ok every time! What on earth was going on?

Checks of the datasheet showed I had it connected properly - or so I thought! I asked on the G-QRP club forum, and they agreed the datasheet. Yet a check of the old Marconi RC-690 RF board the transistor came from, showed otherwise! It turns out that every manufacturer builds these with the expected 'tab to emitter' device layout - all apart from the original designers Motorola! Genuine Motorola parts, which this is, have the tab on the can next to the collector!

So the whole layout of the PA has to be redesigned! Luckily it seems the transistor has survived, possibly because I was very quick in turning the thing off before it got too hot.

BBQ fried eggs - new uses for old equipment panels
 There are a few other issues with the transverter though which im not so happy about. Firstly, I seem to be getting far too much leakage of the local oscillators 42MHz signal through the mixer and into the Tx chain - enough that it is present as an amplified carrier! Likewise, when the 28MHz carrier is fed in for testing, that shows too much leakage. Either there is a mixer problem (doubtful with an SBL-1 DBM) or I need better filtering before the PA stages. Im also worried about correctly terminating the PA during testing, before I have the LPF built. Im not sure of the correct impedance to add a temporary load.

Another issue, noticed yesterday - the Tx buffer transistor gets too warm! This should be a BF199, but as I didnt have any ive been using a 2N3904. Ive now ordered some BF199's to put the correct specified part in place.

The past few nights have seen amazing displays of noctilucent cloud over Europe. The image below was taken at 00:30UTC


Ive also done a little bit towards finally finishing the TDOA direction finder, by making the main boom section of the antenna array. 


Whilst working on this boom, I discovered two of the elements of the UHF section of my tape-measure crossed Yagi for satellite work were off-center. Ive now fixed that, and tested the UHF beam with my MVT-7100 receiver on a number of passed of SO-50. Next step is to add a pair of headphones, couple the UHF beam to the VHF beam, attach the VHF transmitter - and see if I can actually get into the satellite!

Tuesday, 13 June 2017

Clansman Power Indication mod proposals

One of the problems Ive seen that users of ex-military Clansman radio have, is that of inadvertently leaving the set on, and ending up with a flat battery.

Clearly, in its original role, the radio would rarely be unattended. Either an operator would have it on his back and be wearing 'phones, or it would be in a position where the low battery alert (breaking of the squelch three times a second) would be heard.

Not so in amateur use. Besides, in amateur use, its unlikely that any other form of power indication, a light for instance, would cause any hassle, as it might under battle conditions. So, it seems sensible to look at the possibility of providing these radios with a 'Power On' indication.

Electrically, such a thing is about the simplest circuit you can think of! An LED, a series resistor, and a source of power that is constant when the set is switched on. Physically, this could be a challenge! It will involve finding a suitable place on the case of the radio to drill a small hole and mount the LED. It also requires finding where the connection can be made.

Although the PRC-350 is likely to be the easiest of the radios to add a power LED to physically, I dont have the service manuals and EMERs to hand for it! But I do have them for the PRC-351, so have had a look...

There are several supply lines in the PRC-351 - 3v, 6v, 9v, 17v and 100v.  The 3v and 6v lines seem likely to be quite sensitive, and the 17v and 100v too high. So the 9v line would seem to be the supply of choice. I dont want it to take too much current though, but limiting the current to much less than the LED manufacturer specifies will only result in a dimmer light, which is likely to be preferable anyway. Ideally, a low current 3mm LED would be used, to minimise the loading.

I suspect that a usable brightness can be had from a modern 3mm red LED for very little forward current, but I will rig one up on the bench with a 9v supply and a potentiometer and find an acceptable brightness, then measure the pot to find what series resistor is needed.

On the PRC-351, the main source of the 9v line is module 19 pin 3. But, this line can also be found on several other modules - 20 pin 23 (DC switching), 13 pin 10 (Tx AF), 7 pin 9 (Rx AF) and 8 pin 2 (Non linear amp). Which to select would be the one that is nearest to the LEDs position!

I do need to open my -351 up at some point to perform the L/W volume mod described earlier in this blog (to make the Tx modulation level the same in both settings), and to finally add the rubber boot to the 10m conversion switch, so will look at adding a power LED at the same time.

Monday, 12 June 2017

T4 class AB bias - sorted?

As I said I would, I replaced the bias resistor R15 (1k8) for T4 with a potentiometer, which just happened to be on the bench and a value of 4k7. Monitoring the base voltage with one eye, and the current drawn with the other, I adjusted the value of this pot. At some high value, the current actually dropped!, but as the resistance was lowered, I hit the point where the transistor would go into thermal runaway, the current climbing, slowly at first then exponentially faster, up to several hundred mA!

Several attempts later, and I hit on a setting where the meter needle stayed put even after watching for longer than it took to start climbing before. Measuring the pot (and the original resistor, they were in series) gave a value of 2800 ohms.

I replaced the pot and original R15 with a 2k7 unit, but this was too low and the current started to climb. A value higher, 3k3, and the current stays where it is on the meter needle, a total circuit current of around 75mA. I had already measured the circuit up to but not including the driver at 60mA, so the Tx driver is now set taking about 15mA. This might still be too high, but at least now seems stable! Ive asked for confirmation and advice on the G-QRP club forum, that ive done the right thing here.

One ZTX327 left - Taking it steady!

The old Marconi RC-690 PA board had one remaining ZTX327 transistor on it. I have very carefully removed this (not easy on public safety grade equipment designed for shock and vibration immunity), taking care to ensure it doesnt get too hot. On my component tester, the freshly removed device reads a base voltage of 723mV and beta 52.

Testing... Testing...
The removed transistor from the transverter reads 714mV and beta 85. Oddly, this read much higher on the first pass, but then stabilised at 85. I suspect that is down to the tester. But, it seems both transistors are functional. The 1N4148 diode in thermal contact also tested out fine. I can only think that the problem is the bias voltage. I shall replace the 1k8 resistor at R15 with a potentiometer and slowly increase the bias, watching the current drawn as it goes.

Sunday, 11 June 2017

Transverter Setback

More work this evening on the transverter, after that is, building a clothes prop for Julie's washing line!

I spent some time taking some readings of the various stages using an RF probe and DVM. With the 28MHz drive set at 5dBm (the most I can give it) the input to the SBL-1 mixer measured 147mV (this is the 5dBm IF signal), the oscillator input 114mV, and the mixer output around 2mV. The input to the Tx buffer stage 4mV, and the output 30mV. All well and good. I tuned my MVT-7100 scanner to 70MHz USB and even without defeating the squelch could hear the thing from a good 5m away!

After a lot of searching and enquiring after equivalents, I decided first to use a 2N3866 in place of the specified ZTX327 transistor for the driver amp. I had just two of these. Well, I managed to snap the emitter leg off of the first one! So, I built the stage using the second, but then decided to try and find an equivalent to the MRF237 specified for the PA.

Putting down another pad
By an odd coincidence, something on the net linked me to the circuit of the Marconi RC-690 PA strip, where I discovered there is an MRF237 - and I have one of these boards! Trouble was, I couldnt find it! So, after tearing the workshop apart I eventually located this PCB - and discovered that there are some ZTX327's on it as well!

Its from here on that it all started to go wrong!

Getting the ZTX327s off of the board was awkward, and when it finally came, a bloody great blob of molten solder fell on my finger! Thats coming up in a nice blister. I removed the 2N3866, which by this time included all the surrounding parts of the driver amp, and rebuilt it using the ZTX327 i'd just removed. On powering up and measuring the output using the RF probe, all looked great, well over 100mV, but now the input measured only a few mV, not the previous 30mV - it seemed to be badly loading the previous stage... and then I started to smell it!

Oh my gawd it was running hot! Incredibly hot! The PSU's meters showed this stage dragging around 250mA. I powered down and had a think. Back to the books and internet for a bit of research, and decided to check the bias was sensible. Disconnecting the drive by desoldering the leg of the trimmer, I measured the DC voltage on the base - 0.68V, hmmm, seems about right to me? But, it kept dropping, quickly to 0.46V then more slowly. And it still got very hot. I tried a blast of freezer spray and it made no difference, and by this time the clean peaks on the spectrum analyser had degenerated into a mass of sproggies!

I suspect ive killed this transistor! But why? Was the bias at fault? Is the 1uH choke too low in value? Or was the transistor already faulty, or damaged in being removed from the PCB? Because im lazy, and im regretting this now, I didnt bother to test it before hand.

Tomorrow, i'll start this stage again. The old PCB has one more ZTX327 to salvage. This time, however, i'll test it before soldering it in!

Saturday, 10 June 2017

4m Transverter progress

Whilst it was raining this morning, I decided to do a bit more to the transverter. Thanks to members of the G-QRP club forum, I now knew how to arrange the coil L2, which had me puzzled due to its air wound construction and need for a 1t primary. I wasnt sure exactly where to put that turn!

Winding it was fun! I decided to use red enameled wire for the 1t so I could actually see it! The photo below shows it soldered in position.

With this done I could start progressing towards building the amplifier strip, but first I wanted to check how things were doing so far, in particular, the SBL-1 DBM  (Double Balanced Mixer, the left hand silver box with legs) and its Dual Gate Mosfet buffer, needed testing. So after adding the first trimmer capacitor, which gave me a convenient point to connect, and tacking on the resistor chain that takes the supply to the buffer (these become permanent later in the amplifier) I set up a simple test.

With the unit powered, a few checks with the frequency counter were done to check that the oscillator 42MHz was running and appearing in all the right places - particularly the output of the buffer! This done, I fed the mixer with a 28MHz +5dBm signal from my Marconi 2955, and looked for an output

So the mixer is working. 5dBm is a little low for proper testing (around 3mW), and the input to the mixer is designed to be 10dBm (10mW), but 5dBm is the most I can get out of the test set! Next step the pre-driver amp. Another fiddly little 7t air wound coil needed. But, before this, me and Sam had a job to do - run a CAT5e cable to Sams bedroom! This took up most of the day!

In the absence of the specified BF199, ive substituted a 2N3904 in this position. The completed pre-driver section, and the above mentioned, now permanent, resistor chain, can be seen on this photo below. At this stage, getting hungry and it being late, I did a final test, before finishing off for the night.

Thursday, 8 June 2017

PRC-350 Volume Control Mod

One of the problems with the Clansman FM radios, the PRC-350 and -351, is that they have just two audio settings - Whisper (W), and Loud (L). When in W mode, the received audio is attenuated by 20dB, in order that the enemy cant hear your radio. But, at the same time, the microphone gain is also increased by 20dB, so that you can whisper and the enemy cant hear you! All well and good under battlefield conditions, but not terribly good for amateur use! Ideally, what we amateurs want is the mic gain, and hence the Tx deviation, to remain the same, and to be able to change the received volume.

So, being on a short shift today, and having done my good deed for the day dealing with a medical emergency, I decided to use my bit of extra free time this evening to sort this issue out.

The PRC-350 opens up by unfastening four captive hex bolts, and then folds out, taking care with the now very old flexi-connections! The bit I wanted to work on is Assembly 12, which is on the section folded out. Five captive screws hold this board into the case, so had to be undone to lift the board out to access the solder side.

From the service manual, I had found that when W mode is selected, this connects pin 9 of Assembly 12, to ground. This is detailed as the 0VW line. Grounding pin 9 selects a bias capacitor that increased the mic gain by 20dB. A similar line works on the audio amp module for receive, but I didnt want to change that

I first tried cutting the track, but it turned out that the pad to the right is just that, probably for an automatic test jig during manufacture, and the flexi-board connection was made via through hole plating.

So, in order to effect the modification, I got the joint nice and hot and removed the solder with a combination of a solder sucker and desoldering braid. After testing the ensure that the pin was indeed disconnected (with W selected you can do a continuity test to ground, there should be a path from the pad but the pin should be open circuit) I then carefully slid a little sleeving over the pin and into the hole, to insulate it. It can just be seen in the above photo. Finally I wrote the mod and the date on the PCB with an indelible pen.

A bit of adjustment of the audio levels, and I now have a PRC-350 that has the same Tx deviation in both modes, but now the L and W controls are simply a volume control.

The same mod, but I expect slightly different, probably in terms of the connections rather than technique, should also be possible with the PRC-351. That will have to wait for another day.

Ive also bought some superglue today, so could do a bit more work on the 4m transverter now I can glue the pads down! Not much more done this evening, just the Tx IF input attenuator, and a test of the changeover relay.

Next stage requires the positioning of an open air wound transformer - 7t secondary with a 1t primary. The problem I have is that im unsure where the primary should be positioned relative to the secondary!

Amendment - Ive had a few moments spare while my tea settles, to look at the service manual for the PRC-351. Exactly the same method is used in the -351 as the -350. In W mode, a connection to the Tx audio module is grounded. As it happens, it is again pin 9, but in the -351 on Assembly 13.

Wednesday, 7 June 2017

Two Projects completed

Managed to get some time in the workshop today to get the Dew Heater Controller and the Clansman PRC-350 Battery Conversion finished. Started with the Dew Heater, this required a lot of wiring up! I also discovered a mistake i'd made, in wiring ALL the connector tags to ground - the Heater outputs needed a common Vcc connection!

Again, liberal use of heatshrink, mostly colour coded. A range of tests carried out as construction progressed, including checking that the Arduinos on-board regulator could handle 13.8V (ive had some blow!), and that the device recognised the temperature sensor on each port. This at first didnt work, but that was because I had wired the sensor chip up to the phono lead backwards! A final check with the temperature sensor, heater band, and a can of freezer spray, showed all to be working properly. All that is left now is to label everything up and put the lid on!

So next up came the LiPo battery for the PRC-350. This wasnt a complicated task, but was difficult! First, another cutout was needed for the switch that will control the external auxiliary outputs. I managed to measure this wrong (or rather, right but in the wrong place) and drilled a 12mm hole then filed it out for the rectangular shape of the rear of the switch. It was only then that I realised that the part of the switch that will actually sit through the panel was round like the front! So I remeasured, and with a very bouncy and complaining step drill bit, expanded the whole to 20mm

Partly cut switch hole

Switch fitted in its 20mm hole
A further cutout had to be drilled and filed for the USB charger module. At least there were no surprises in the shape of this! However, this is where it became difficult. I now had to solder and connect various wires inside a very small closed box.

Again, for very obvious reasons of there being essentially a 15V 3A 30C bomb in the box, liberal use of heatshrink was required.  I also managed to wire the main switch to the battery terminals directly forgetting to fit the fuse! Another bit of corrective work and the fuse holder, plus 2A fast blow fuse, was connected The battery terminals were then reconnected, and coated in hot melt glue to insulate the screws.

A very liberal sloshing about of hot-melt glue then to secure the low voltage monitor and the USB charger modules in place.

A few bits of foam were inserted then to hold the battery in place and to stop it bouncing about in the box, and the switch, DC jack and USB output tested. So, if required, this pack can provide 5V out from the USB for general use charging phones or running small devices, and 15V up to 2A for other uses. I would anticipate that being used for devices with their own internal regulators!

As can be seen in the above photos, the low voltage monitor comes into play when the shorting plug is attached. I do still need to attach a lanyard to this to the battery case to avoid it being lost. The battery is also now marked, like the 24V LiPo pack for the PRC-320/-351, with red, in this case a band of red PVC tape around the top, to mark it out as requiring special charging.

The last thing to do was to build the balance charge cable.

With the five connections made, sleeved and tested, the D-type was fastened away in a shell. The whole pack was then put on a balance charge, ready for use.

With these two projects completed, I cleared off the bench (which by this time was a filthy mess of cut bits of wire insulation and solder blobs), and started to set up ready to do a bit more on the 4m transverter, which I have neglected for far too long.

Friday, 26 May 2017

Spares Sorting Tedium and Siamese Capacitors

One of the problems with obtaining spares and parts via the acquisition of surplus, is that often everything is all jumbled up together! And so at some point, either when space is running low or more normally when moaned at by the wife, I have to endure the tedium of sorting bags of mixed random parts out into their individual values or part numbers. First up, was an old ice cream box full of, mostly, semiconductors

 These turned out to be a very eclectic mix of transistors, diodes, a few power SCRs, and a good smattering of voltage regulators

Before moving onto the next bag, I put some time into the 40m Direct Conversion receiver Bob M1BBV has asked me to work on. This is something he picked up on ebay already 'built'. It was working to an extent, but had some construction problems

Ive sorted out the badly placed parts, dealt with the poor soldering, and fixed the bad connections. There may be an issue with the level of output power, but that can wait. It seems to give about 70kHz coverage, so Bobs asked me to put it down at the CW end of the band

Boxing it up proved a bit tricky as the Chinese design is not perfectly symmetrical about the tuning pot, so aligning the holes was a bit awkward. There was also the issue of the 'preset mod' that can be seen at the top of the picture, slightly off board. No one knew what this was! It turns out its to adjust the level of the sidetone volume!

But that was enough of that! Yesterday was extremely hot and sunny, so instead of radio or electronics, I spent most of the day gardening! But, when it was too hot, I sorted out a big bag of mixed capacitors!

 These were mostly quite vintage types! But they will be fine for non-critical applications. With so many to sort, it was still a surprise to come across a conjoined pair!

 Then, in the cool of evening, I returned to the workshop. Further work on the wiring of my Dew Heater Controller, now not too far from completion, plus the construction of a scaled down version of DL4YHF's CW Keyer, this time with no memory buttons, again for Bob

 Today is yet again Scorchio, and the workshop at present too hot to be comfortable working in.