[Elecraft] K1 Internally Generated Signal (Long Response)

[Don Wilhelm]

Mike,

Are you misinterpreting the meaning of "zero-beat"?
Zero-beat does not mean tuning the signal to zero audio frequency.

It does mean that the signal is tuned to the same pitch as another tone 
(the sidetone).  When the two tones are close in frequency, you will 
hear a 3rd low pitched tone - that is the 'beat note'. Its frequency 
will be the difference between the two tones, and will be heard as a WOW 
WOW sound.

When the WOW WOW tone gets slower and slower and finally the rate goes 
to zero, that is "zero beat".

So yes, when properly calibrated, and tuned to the carrier of WWV at 10 
MHz, the K1 frequency display is reading 10000.0 which is where the K1 
will transmit.  If the BFO trim cap has been set properly, that carrier 
will be heard as a tone equal to the frequency you set as your preferred 
sidetone pitch.

Yes, if you 'do the math' on the VFO, Pre-mixer crystal and the BFO 
frequencies, you will find the frequency they calculate to is different 
from the dial frequency by exactly the pitch of the received tone, but 
that is not relevant to the use or the calibration of the K1.  One does 
not have to consider whether the receiver is using LSB mixing or USB.  
The offset is automatic when you set the BFO trimmer cap correctly.  The 
filter center is 4913 kHz (plus or minus a bit depending on the exact 
crystal set used), and to produce a 600 Hz tone, the BFO must be 
displaced by 600 Hz from that filter center - once that is done, the 
user does not have to be aware of the rest of the mixing frequencies - 
the dial reads the carrier frequency, pure and simple.

BTW, the K1 and many of Dave Benson's transceivers are quite similar - 
two Gilbert cell mixers and separate adjustments for the TX oscillator 
and the BFO.  The SWL series is the closest to the K1 design, but that 
does not inject the pre-mixer for mixing the VFO with a crystal for 
multiband use as the K1 does.

73,
Don W3FPR

On 10/29/2013 5:05 PM, Mike Morrow wrote:
> Don wrote:
>
>> While what you say about the K1 display indicating the transmit carrier
>> frequency is technically correct, I believe you are over-complicating
>> things.  The K1 (and all Elecraft products) properly calibrated will
>> indicate the transmit carrier frequency - so when receiving 10 MHz WWV,
>> the display should indicate 10000.0 kHz, and the transmit frequency will
>> be at that same frequency...
> Hi Don,
>
> I agree completely with the contents of your post.  But...the last sentence
> quoted above is true **for the CW-only K1** only for the reception of a
> **CW signal** that is producing a tone in the user's headphones that is
> equal to the CW offset between the receiver zero-beat frequency and the
> transmitter frequency.
>
> I'll use an example.  Assume that a signal being received and the K1's
> transmitted signal are both exactly on 10000.0 kHz.  The properly-adjusted
> K1 display shows transmit frequency at all times (10000.0 kHz).  Next,
> assume this K1's CW offset is 600 Hz.  In order to hear a beat frequency
> (AF tone) equal to 600 Hz, the K1 LSB receiver's *zero-beat* frequency
> must be 600 Hz *above* the received 10000.0 kHz signal...10000.6 kHz.
> The K1's LCD indicates 10000.0 kHz, but a signal received on 10000.0 kHz
> produces a 600 Hz beat note.  The only signal that would produce zero-beat
> in this K1 is 10000.6 kHz...the receiver zero-beat frequency.
>
> But as you have said, we do *not* define the K1 CW receive frequency as
> the frequency of a signal (10000.6 kHz) that would produce zero-beat.  We
> define it as the frequency of a signal (10000.0 kHz) that would produce
> an AF tone equal to the CW offset (600 Hz).  We reach the same conclusion
> that the 10000.0 kHz displayed is correct for both transmit and receive,
> regardless of how we approach it.  :-)
>
> OTOH, when we use this K1 to copy the LSB of WWV's 10000.0 kHz *voice* signal,
> we have no mode switch on the CW-only K1 as we have with multi-mode receivers
> that eliminates offsets in receiver frequency and displayed frequency.  We
> *must* tune the K1 receiver to zero-beat WWV's carrier (10000.0 kHz) in order
> to copy its LSB voice signal.  Since the K1 LCD shows transmitter frequency
> ...0.6 kHz below the receiver zero-beat frequency...this K1 will display 9999.4
> kHz as we copy those solar terrestrial indices at 18 minutes past the hour. :-)
> If we transmit while zero-beat with WWV, anyone nearby who is listening to
> WWV's LSB voice will hear a 600 Hz tone resulting from our 9999.4 kHz signal.
>
>> If one follows the instructions in the manual, everything will
>> "fall into place" ... Done, no "fussing" - the key is that you tune
>> a received signal to the same pitch as the sidetone - the rest is
>> automatic.
> We again have no differences.  Once in a while someone will come along
> who thinks that setting the K1 sidetone in the menu will also set the
> CW offset as well.  No such luck...that would be nice, but think of
> the added complexity to make that happen in a K1!
>
> I do not use Spectrogram...it's too sophisticated for me!
>
> It really wasn't my intention to raise a discussion of K1 transmit and
> receive definitions and offset adjustments.  I just thought it necessary
> to explain why the spurs I listed in the original posting,
>
>> The spur just below  7000 kHz occurs at  7 x 999.875 =  6999.125 kHz.
>> The spur just below 10000 kHz occurs at 10 x 999.875 =  9998.750 kHz.
>> The spur just below 14000 kHz occurs at 14 x 999.875 = 13998.250 kHz.
>> The spur just below 21000 kHz occurs at 21 x 999.875 = 20997.375 kHz.
> show up at zero beat on the LCD of a properly-adjusted K1 with 600 Hz
> offset as follows:
>
>> the  6999.125 kHz spur...zero beat should be  6998.525 kHz,
>> the  9998.750 kHz spur...zero beat should be  9998.150 kHz,
>> the 13998.250 kHz spur...zero beat should be 13997.650 kHz,
>> the 20997.375 kHz spur...zero beat should be 20996.775 kHz.
> I could have said that instead of a zero-beat when tuned any of the four
> frequencies shown above, my example K1 will produce a 600 Hz tone when
> tuned to 6999.125, 9998.750, 13998.250, or 20997.375 kHz.  That avoids
> the detail of CW offsets and sidebands.  But I can never tune for any
> AF frequency just using my ears more accurately than tuning for zero-beat.
> Dave Benson 15 years ago designed the firmware in his wonderful DSW-series
> of mono-band CW rigs to require that the CW offset be set while comparing
> two AF signals, one at 800 Hz, back and forth until they were both at
> 800 Hz.  Nasty work!  That and mode B-only iambic keying were about the
> only things I did not like about the several DSWs that I built.
>
> Thanks for your comments and for reading my approach.
>
>