[Central-Electronics] Ce 20A alignment questions

[Laurence M. Szendrei]

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
> ______________________________________________________________
> Central-Electronics mailing list
> Home: http://mailman.qth.net/mailman/listinfo/central-electronics
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Central-Electronics at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html