[Central-Electronics] Ce 20A alignment questions

Tue May 5 01:27:14 EDT 2026

Thanks everyone for all the answers. It was actually the article that Ron posted that got me to take my 20A down off the shelf to work on it. Even with that article and the manual, I somehow hadn’t gotten it through my head  that adjusting distance between  L1 and L2 sets relative levels of the two RF phases. Alan explained that. 

The ZL2AMJ method is clever. I hadn’t heard of it. I have been using an SDR with an RF pickup off a dummy load which seems to give a pretty clear picture of the situation.

Laurence mentioned the 100V. I have one of those. I brought that back to life many years ago. It does achieve better opposite sideband suppression with a more sophisticated audio phase shift network and a simpler (!) RF phase shift network. But the 20A is such a historic transmitter and lean by comparison, much easier to muscle around.

I have to shelve the project for a week. When I get back to it, I’ll let you know how it goes or maybe ask more questions.

I really appreciate the responses,

Jon

> On May 4, 2026, at 4:41 PM, Laurence M. Szendrei via Central-Electronics <central-electronics at mailman.qth.net> wrote:
> 
> Bob - I like ZL2AMJ's method too - it's much better than using a very narrow RX. (Before I had a software-defined RX I used my R390 with the bandwidth in the 100Hz position to null out the undesired sideband, and tuning back and forth as one checks the suppression in the LSB, then USB, mode, back and forth.) I never thought of listening for a tone 2X the frequency of the signal at the audio input! It would be good to have the SDR listening in the AM mode with a bandwidth wide enough to capture both sidebands and get both the visual and audio "feedback" (not in the electronic sense!) while performing the nulling procedure. Thanks for getting me thinking!
> 
> 73,
> -Larry/NE1S
> 
> On 5/4/26 11:43 AM, Robert Nickels via Central-Electronics wrote:
>> On 5/4/2026 6:19 AM, Laurence Szendrei via Central-Electronics wrote:
>>> Also, if you have a local SDR with a spectrum display use this to do your sideband suppression procedure - it’s so much better at telling you directly what is happening regarding sideband suppression than using a scope or any receiver lacking a spectrum display. CE didn’t have these when it developed the procedure in the manual
>> 
>> I'll just "second" what Larry is suggesting here.   Even a cheap SDR is more than adequate - just make sure to loosely couple to the transmitter so you don't overload it, and choose SDR software that lets you zoom way in on the signal so you can clearly see both sidebands and the carrier.    You'll see the interaction between controls but as described in the manual, it's a process of optimizing to get the best compromise when switching between sidebands.
>> 
>> Another very useful method must be credited to Fred Johnson ZL2AMJ who first described it.   Think of the spectrum produced by an SSB transmitter when modulated by a pure 1 kHz sine wave tone.   With good carrier and opposite sideband suppression,  only a single output will be produced (this is how many produce CW).    If there is carrier leakage,   it will be 1 kHz removed from the desired signa,  thus a the beat frequency, a 1 kHz tone,  will be heard in the output when listening with an AM detector.    If there is opposite sideband leakage,  it will be 1 kHz on the other size of the carrier thus a 2 kHz tone will be heard.    The amplitude of the two tones heard with an unaligned phasing exciter will give an indication of the unwanted signal components that are present.  Nulling the carrier should bring the 1 kHz tone down virtually into the noise.  Then as you adjust the audio and RF phasing you'll be able to minimize the 2 kHz tone.  It's an iterative process because the adjustments interact, and the optimal setting for one sideband won't be optimal for the other sideband.   You just have to go back and forth til you get a good compromise and as Larry said,  it's possible to get 30db or better suppression.  The improved audio section of the 100/200V allows greater suppression than with the 10/20A design.
>> 
>> Fred described a simple "crystal radio" type detector with headphones but all you need is an AM receiver but using an SDR in the AM mode gives the added benefit of a visual indication.
>> 
>> 73, Bob W9RAN
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