[Elecraft] N6KR method for setting the reference and a bit on Zero Beat

[Don Wilhelm]

John,
It was Wayne's posting on the reflector.  It will be in the reflector
archives.

I have copied the text of Wayne's note below.

BTW - the key to success with this method (as well as many others) lies with
the ability to zero beat accurately.  Zero beating seems to be something
that is not really done very often with modern frequency tracking
transceivers, so it may be that we are losing a skill among amateur ranks.
When we operated with separate (non-frequency tracking) receivers and
transmitters zero beating was something we had to be able to accomplish, so
the old timers will know how, but newcomers don't seem to catch on.

Zero beating is NOT trying to tune to hear zero frequency - neither our ears
nor the receiver's audio can detect that.

Zero beating IS detecting the frequency difference between two tones.  When
there are two tones present, a third tone is also produced (actually a 4th
too, but we ignore that).  This 3rd tone is the frequency difference between
the two tones. (the sum is also procuced which is that 4th tone if you were
curious).  Remember your high school physics classes on the behavoir of
oscillating strings.

When the first two tones are separated by only a bit, it sounds like the 2
tones are changing amplitude at a slow rate - this is the BEAT NOTE and is
what we are listening for.  When the rate of amplitude change slows down to
zero or almost zero (BTW, we CAN hear that), you are at zero beat.  In
summary, we must have 2 tones close to each other in frequency to begin to
hear the beat note - when they are exactly the same frequency, the beat note
goes to zero (the two tones meld with each other and become one).  It is
easier to hear the beat note if the two tones we are trying to match are of
similar amplitude (use the AF gain control so the level of the received tone
is about the same as your sidetone level).

 If you have tuned a stringed instrument, you likely have used  the zero
beat method to match the tone of 2 strings, so you know what zero beat
sounds like.

Another recourse to detect the pitch of tones is to use a crutch, like
Spectrogram (I do that too - sometimes it is just easier that way!!!)

73,
Don W3FPR

----- Original Message ----- 

| I have followed this thread with some interest.  But, where do I find
"N6KR
| method for setting the reference"?
|
| Didn't see it on the Elecraft web site.
|

-------------------text of Wayne Burdick's reflector posting of August 20,
2003 ---------------

 All of the methods that have been described for calibrating the K2's 4-MHz
oscillator will work. But I use a different technique that allows C22 on the
Control board to be set to precisely the correct position, with no
guesswork.

This method relies on the following simple observation. If you tune in an
on-air
signal at a known frequency, the difference between the *measured* VCO and
BFO
(using CAL FCTR) *must* equal that frequency, or C22 is not set correctly.
(Actually, this holds for 160-17 m; on 15-10 m it's the sum, or VCO + BFO,
that
must equal the signal's frequency. But it's easier to do the adjustment of
C22
on 17 m or lower because you don't have to do any math at all, as I'll
explain
below.)

Here's the procedure. It requires revision 2.XX firmware, and assumes you
have
already done Alignment and Test, Part II, at some point. The K2 should also
be
allowed to come up to room temperature.

1. Tune in a signal at a known frequency. Use one that's at an *exact* kHz
boundary, so you can easily see when the VCO and BFO readings match in step
2.
(I use WWV at 10, 15, or 20 MHz.) Use USB or LSB mode rather than CW, so
that
there will be no CW receive offset. In the case of a K2 I was calibrating,
the
VFO read 10000.17 when the signal was tuned in perfectly. If it had read
10000.00, no further improvement would have been possible.

TIP: Zero-beat the carrier precisely, or listen to a voice signal and adjust
the
VFO for the best quality. The more accurately you tune in the signal, the
more
accurately you'll be able to set C22, below.

2. Run CAL FCTR. Now alternately move the K2's internal counter probe
between
TP1 (VCO) and TP2 (BFO), adjusting C22 in small increments until the kHz and
Hz
digits at the two test points match as closely as possible. In my case, the
two
readings matched at 14913.60 and 4913.60. The difference is exactly
10000.00--the frequency of the on-air signal.

3. Put the counter probe on TP1 (VCO), switch to 40 meters, and run CAL PLL.

4. Put the probe on TP2 (BFO) and run CAL FIL. For each operating mode, vary
each filter (or BFO) setting up 1 count, then back down, to force the K2 to
take
a new BFO measurement for each and store it in EEPROM.

The VFO dial should now be very well calibrated.

If we get a lot of positive feedback on this method, we'll post it as an
application note.

73,
Wayne
N6KR