[Drake] TR-4C SSB Pitch issues

[William Houghton]

Dave,

I'm not sure what you mean by thin and sharp.

The TR-4C uses a 9MHz oscillator to feed a balanced modulator. The audio from V18 is also applied to this modulator. The result from this is a double sideband supressed carrier signal which is passed through one of the two crystal filters (selected by the sideband switch). The filter will pass one of the sidebands and reject the other. To keep it simple let's say that the audio bandwidth for SSB is 2.4KHz. Then one of the filters will pass signals from  8.9976 MHz up to 9MHz. The other will pass signals from 9MHz up to 9.0024MHz. If your 9MHz oscillator is off frequency the output of the balanced modulator isn't going to be the same as the passband of the crystal filters.

The manual tells you to adjust this by listening to the pitch and adjusting such that its the same for both sidebands. This does work and you can get pretty close if everything is working correctly. The problem that I have encountered is that the audio level on receive is not nearly equal from one sideband to the other on both of these radios. One of the sidebands seems to be about a third the audio volume of the other. Until I fixed this issue I wasn't able to hear the pitch as I switched back and forth between sidebands. On my TR-4C this audio volume problem seems to be an issue with the sideband switch that was solved with DeOxit. I'll try to do the same with my TR-3 if I can figure out how to get the cover off of the crystal filters "can" that houses the crystals and the sideband switch.

In my case, this "volume" issue affected the transmitter drive (easily observable with a monitor scope and a 1KHz tone generator  - thank's to Heathkit for including one in my monitor scope).


Good Luck,

Bill




________________________________
From: GGLL <nagato at arnet.com.ar>
To: Drake <drake at mailman.qth.net>
Sent: Sun, June 6, 2010 8:24:09 AM
Subject: Re: [Drake] TR-4C SSB Pitch issues

    I think the problem is the carrier point adjustment, not the injection 
crystal oscillator, so, no it's not; you must refer to 5.9 (the previous 
adjustment) 9.0 MHz oscillator.
If the crystal filters are too old, it's  probably you won't get the 
same audio tone in both sidebands.

Regards
Guillermo - LU8EYW.

El 05/06/2010 23:31, David Walker escribió:
> Hi,
>
> I have heard my TR-4C on air and the audio is very thin and sharp.
>
> I was just wanting confirmation that the alignment procedure to balance
> the carrier injection point is listed under page 5.10 of the manual as
> INJECTION CRYSTAL OSCILLATOR.
>
> Is this right?
>
> Regards
>
> Dave
>
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