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Author Topic: Central Electronics 100V Opposite Sideband Supression Adjustment  (Read 733 times)
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AJ1G
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« on: April 26, 2024, 01:52:52 PM »

Just brought one of the two CE 100V exciter/transmitters that I bought from Andy WA2CDLís estate sale last year up and running.  So far so good, seems to be working well
overall.  However, opposite sideband suppression could be a bit better.  Iíve tried the procedure in the manual to tweak the balanced modulator audio ratio and balance pots which has improved things a lot but Iíve run out of pot adjustment at the stops. The manual says for future improvement , adjustment of the 8 Mc oscillator phase coils is required.  So, how to proceed with that?  Tweak each one a little at a time and then fine tune with the pots?  Before I start tweaking the coils should I put the pots back approximately mid span where they were before I tweaked them?
 
BTW, the full carrier AM mode performance of the 100V is pretty good, have been using it to drive the CE 600L to 100 watts carrier output.
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Chris, AJ1G
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« Reply #1 on: April 26, 2024, 04:47:11 PM »

Chris,

I use a dual trace scope with these phasing type exciters to adjust the RF network phase shift, it makes it much simpler than dealing with the interaction that occurs when you are going back and forth between the audio and RF adjustments. 

Do set the audio pots back to center range if you are going to try to use the scope technique in the manual.

Phasing setup is pretty easy and painless if you have access to a dual trace scope.  I use a spectrum analyzer for the final adjustments but once you get the RF phasing right, a modern highly selective SSB receiver makes for easy adjustment of the carrier and audio balance controls to finalize the setup.

Rodger WQ9E
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Rodger WQ9E
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« Reply #2 on: April 26, 2024, 09:16:10 PM »

Thanks for the advice Roger.  Iíve dialed it in as best I could using a Wandell and Goltermann AT-611 selective level meter to look at and listen to the relative signal strength of the desired and suppressed side bands and Iíve also looked at the spectrum and waterfall display on my IC7300 and also on air with remote web SDRs.  I do have a dual trace scope, the Tek 422 that is my duty AM modulation envelope monitor.
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Chris, AJ1G
Stonington, CT
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« Reply #3 on: April 27, 2024, 07:38:59 AM »

Chris,

Your 422 will work fine for checking phase relationship between the two RF "channels".  Start by connecting both probes to the same RF phase to check to make sure that there is no phase shift due to an issue with your probes/preamp channels.

I use pretty much old school Tektronix gear; a pair of 7854 mainframes with an assortment of plug-ins are my bench scopes along with a 7623 storage mainframe equipped with a 7L13 spectrum analyzer plug-in.

Rodger WQ9E
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Rodger WQ9E
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