Saturday, 11 June 2016

Modification Results - Good, and Bad

Having finally completed the mods (apart from the S-meter one) on the RT-320 Testbed radio, ive brought it in to the shack to test, and see how they have done.

Well, on a positive note, the diodes do not effect the operation of the synthesizer. Thats very good, as that means I dont need to provide an alternative, boosted 3v supply to the decade switches. I managed to track down which of the wires was the 3v supply from pin 19 of the synthesizer module, and reconnect that minus the diode.

On a much less positive note, it seems the 2kHz offset mod and/or the CW(W) to LSB mod have not gone quite right. It works perfectly on USB, ive got the set listening to RAF Volmet on 5.450MHz right now, with the dials set to 5.450! But I cant find a signal on the CW(N) setting to check against!

Now, if I select CW(W), which should now pull an added white wire to 0v to switch in whatever LSB module I add, I get RAF Volmet, but with a 2kHz offset!!! Now, im not sure if this is right or not?  I think that in this mode I should be getting an offset SSB signal, as the SSB filter is switched in, and the offset is still applied in this mode. When an LSB module is added, it has the job of muting the USB. But, my new white wire which is meant to go to 0v on CW(W) selection, seems to be at 0v anyway, regardless of switch setting!
I think I need to find a CW(N) signal to check that mode!

One thing I have discovered is that the radio needs a damn good re-alignment! much of 7MHz is out of lock, including the amateur band! And it has a weak unready tone, with lots of noise, which is odd.

I will see what happens if I use the white wire to apply an USB mute signal...

Update - after finally finding a steady carrier that I could resolve to a beat tone of suitable pitch, which turned out to be the 'white' carrier of Hamburg Meteo WEFAX on 7.880MHz, I have been able to switch between USB and CW(N), and find that the tone remains of the same pitch, so the offset mod has worked on CW(N).

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