From: Garey Barrell 
Subject: Re: [drakelist] Sidetone quality/pitch


David -

See Below

David Austin wrote:

  > Regarding CW mode:
>  
> 1: If I operate with the receiver "unmuted" then I effectively get a 
> sidetone by direct reception of the TX output, which also accurately 
> reflects my transmitted carrier frequency (=CW pitch) relative to the 
> station I am working. The other advantage to this mode is a nice pure 
> tone to listen to (as opposed to situation in question 2 below). Is 
> there any known risk to the RX front end from operating it in this mode? 
> Can't think that there would be but thought I should check.

Works fine,  _as long as_  you are transmitting "near" your 
receive frequency.  Not so hot for "split".  The isolation 
of the antenna relay is adequate to keep from damaging the 
receiver front end.

> Wouldn't it have been better to implement sidetone in this way anyway, 
> with a major reduction in RF gain "switched" in the the RX
front end by 
> the TX relay when in TX,  together with preset AF gain to set audio 
> level? A few extra components in the RX, granted.

Yes, except for the above situation.

> 2: In the above situation I operate with sidetone (anti-vox) turned to 
> zero to mute the sidetone. If I do use sidetone (RX muted of course) I 
> find that the sidetone does not sound very pure (a bit
"raspy" or rough 
> sounding). Is this normal or should the sidetone sound like pure 
> sinewave output? Also, is there any way of altering the sidetone 
> frequency? I find it a little too high pitched for my taste. This is the 
> advantage of method 1 where you can choose your own
"sidetone" frequency 
> by adjusting the incoming signal to taste on the RX, then
"netting" TX 
> VFO to same frequency in Spot mode.

Yes, the sidetone is a little "rough" in normal operation. 
I think it's just distortion from overdriving the audio 
stage, but never really tried to track it down.

> Regarding SSB netting (spotting):
>  
> Can anyone explain the source of the canary "warbling" sound when 
> netting the TX and RX ? Is it the sound of the two carrier oscillators 
> beating? If so, why is this not audible as a pure sinewave beat 
> frequency, with a smooth reduction to zerobeat as the two frequencies 
> coincide, instead of the somewhat "unstable" sounding canary sound?

Again, I've never really tried to figure it out.  Obviously 
it is an "audio" beat rather than an "RF" beat.  In any 
event, it is  _FAR BETTER_  than a simple beat, because you 
can easily hear a difference of less than one 
cycle-per-second.  This is impossible with a "normal" zero 
beat of two RF signals, although if the two signals are 
close in amplitude as well as frequency you can watch the 
S-Meter fluctuate at a sub-cycle rate, IF you can get the 
two signals that close.

> Apologies for the many questions in one posting!

Questions are GOOD for you!

73, Garey - K4OAH
Atlanta

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