[Central-Electronics] Sideband Suppression

[K6JEK]

I could find fault with your procedure but considering the rather  
unexciting results I've been getting using all sorts of gear I'd  
guess your technique probably does as well as mine.

After turning the RF phase adjustment inductors hither and yon to see  
if I could improve the opposite sideband rejection I thought I ought  
to reset them and start over -- adjust them for a 90 degree shift of  
the 8 MHz oscillator.  I dutifully took out the MOD DIODES and MOD  
CAPS, hooked up my scope to pins 6 & 7 of the MOD DIODES socket and  
used the X-Y setting to tune for a circle.   I checked the scope  
calibration first.   This was a bust.   One of the adjustments, the  
right one didn't do much.   The left one improved it ever so slightly  
from a squashed ellipse to a not so squashed ellipse.  No one would  
confuse it for a circle, however.  On the next try I adjusted the  
sensitivity of the two probes to compensate for the slight difference  
in signal amplitude.   This didn't help either.  Of course, the  
various caps in there, C111, etc., are running interference.  In the  
end this did nothing except require changing all the other controls  
to get back to where I started.

While I had the mod caps out I tested them on my handy dandy LCR  
meter.   The highest was 5.049 uF, the lowest 5.023 uF.  The  
certainly must be close enough.   It sure would have made me happy to  
find one of those out of whack.

So I've left it 30  dB down everywhere except 45 dB down in a trough  
around 1 kHz.   Until I'm up for taking a more serious run at this,  
I've decided to talk in a monotone centered on 1 kHz.   It takes  
practice.

Cheers,

Jon

On Mar 14, 2008, at 5:17 PM, Lynn Fisk & Georgia Keysor wrote:

> Greetings to the group.  This is my first post.  WD5JKO referred to  
> our 3870 Boatanchors Net in his last post, and I read with  
> considerable interest, the discussion on sideband suppression.
>
> Being a social worker rather than a technician, my way of getting  
> there has been a little different.  I call it the "low life way of  
> adjusting for sideband suppression."  For all the years that I have  
> fooled with phasing rigs, I have simply placed the mic in front of  
> the speaker of a good selectable sideband receiver, keyed down,  
> with the exciter on one sideband and the receiver on the other, and  
> tuned for minimum feedback. I have done this with several CE rigs,  
> HT-37s, and one home brew rig with pretty good results.  The rig  
> Jim heard on Wednesday was set up this way.
>
> I've always wondered what my work would look like if compared with  
> the same station set up properly with a scope.  One of these  
> days............
>
> 73, K5LYN.
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