More: [Central-Electronics] 100V sideband suppression adjustments

[Kannegaard]

The suppression is very uneven across the audio spectrum.   I got 50  
dB at 1 kHz, 35 dB at 2 kHz and a measly 25 dB at 400 Hz.   I have  
never cracked open the audio phase shift network, the PS-2, because  
it's full of those impossibly precise parts, .1%, with crazy values  
like 973.500 ohms, stuff like that.

So in addition to my earlier question, advice on a sideband  
suppression procedure, gosh, has anyone tackled the PS-2?

Thanks,

Jon


Begin forwarded message:

> From: K6JEK <k6jek at comcast.net>
> Date: March 12, 2008 3:49:30 PM PDT
> To: central-electronics at mailman.qth.net
> Subject: [Central-Electronics] 100V sideband suppression adjustments
>
> Does anyone have a better procedure than the one in the book for  
> adjusting sideband suppression on the 100V?
>
> I used the one on page 39 even using the MM-2 as the AF signal  
> source and adjusting for minimum ripple.   I got about 37 dB of  
> opposite sideband suppression with a 1 kHz tone.   I ought to be  
> able to do better.
>
> Next I used my Flex Radio SDR 1000 as a spectrum analyzer and a DSP  
> 599 as the AF signal source.  The DSP 599  turns out to be cleaner  
> than the AF generator in the MM-2.    Fooling around with the four  
> controls, AF BALANCE, AF RATIO and the two RF SHIFT inductors I was  
> able to do a little better, at least I thought so, 45 dB.   That's  
> about the same as the carrier suppression.   But when I put real  
> live audio into it, like a microphone, I don't see anything like 45  
> dB, more like 20 dB.  I really don't understand that.  It's a  
> complete mystery to me.
>
> Anyway I have twisted those four controls with abandon without  
> really understanding what I was adjusting.   I was just watching  
> the spectrum, trying to make the bad peaks small.   Now the control  
> are in some random state compared to where they started.   I'm game  
> for a more methodical approach and have access to modern test  
> equipment.    For example, is there a way to set the phase shift  
> adjustments first to some appropriate spot?
>
> Have any of you come up with a step by step you'd recommend, or how  
> about just helping me guess at one?
>
> I did replace the MOD CAPS a few years ago with matched 6 MFD  
> aluminum electrolytics.   Perhaps I should do this again before I  
> beat my head against the wall some more.   I also replaced the MOD  
> DIODES.   The audio limiter is bypassed but the audio filter is in  
> the circuit.   The other usual stuff has been done except for the  
> mixer adjustments.
>
> Any thoughts would be most appreciated.
>
> Thanks,
>
> Jon, K6JEK_______________________________________________
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