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!

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