Re: CW-Pitch 600 Hz or 700 Hz or what?

Posted by Vic K2VCO on Nov 14, 2005; 5:11am
URL: http://elecraft.85.s1.nabble.com/CW-Pitch-600-Hz-or-700-Hz-or-what-tp383635p383641.html

Geoffrey Mackenzie-Kennedsy wrote:

> Not quite Vic.  The BFO knob would control the frequency of a BFO thus
> establishing the frequency difference between the BFO and a desired
> signal in the receiver passband, as done in receivers for decades.Its
> output is fed only to the product detector when in use. So the knob
> allows you to vary the beat note or pitch. Tweaking the BFO knob would
> and should not affect the sidetone at all, since sidetone is usually
> only a transmit aid.

What I should have said is that the sidetone frequency setting -- a
digital value in the eeprom -- (not the sidetone itself, which as you
point out is not important) is used to compute the dial reading and the
transmit offset.  So I suggest that you need to change this setting AND
the BFO frequency.

If you change the sidetone pitch in the menu (i.e., change the 'sidetone
frequency setting') in the K2, you adjust the transmit offset as well as
the monitor pitch.  The trouble with this is that the BFO frequency
doesn't change, so the passband is still centered on a signal whose
pitch is what you used when you did CAL FIL, and if you have a narrow
filter, you lose gain at the new pitch.

If you change the BFO frequency by itself, then you don't lose gain,
since the relationship between the signal frequency (in the IF) and the
crystal filter hasn't changed.  But the dial reading and transmit offset
are off.

Your solution of adding a second BFO just for receiving would
theoretically work, except that you would need to use the 'real'
sidetone pitch for zero-beating.


--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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