[Elecraft] beat freq method

[FredJensen]

There's a reason why mathematicians speak with equations rather than 
words. ;-) Scott is entirely correct, the sidetone signal and the audio 
signal add linearly in the K3 audio amplifier stage(s) and what you hear 
is their algebraic sum.  If my choice of words implied that the effect 
was non-linear mixing, it was unintentional.

Being an OF from the days of receivers, transmitters with VFO's, and 
modulators, often on separate chassis',  getting on someone's frequency 
entailed turning your VFO [only] on, and adjusting it until its signal, 
as heard in your receiver, added algebraically with the AM carrier or CW 
tone until the exact effect in REF CAL took place ... as the VFO 
approached the audio tone of the signal, they began to fall in and out 
of phase with each other slower and slower, and you heard the "beat" [or 
slow pulsing in amplitude] between them.  When that "beat" stopped [or 
got very slow], your VFO was "Zero Beat" and you would transmit on the 
same frequency as the other station ... if you transmitted fairly 
quickly ... VFO's in those days tended to drift around some unless they 
were built by Art Collins.  And, thus the origin of the term "Zero Beat."

Let's assume your VFO signal was 250 cycles higher  than the frequency 
of the other station.  You would then hear it, the other station, and a 
250 cycle component from the algebraic sum of the two, just as you would 
hear a 1 cps "beat" as you got the VFO within 1 cycle.  I suppose a 
musician with a very good sense of pitch might be able to identify the 
three frequencies involved [other station's note, VFO note, and 250 cps 
sum], but I can't.  What I can tell is that there is a component in 
there and which way to move the VFO to achieve zero beat, and nearly 
everyone else can do that as well.  That's all that's required for the 
Method 2 REF CAL.  If you are deaf, just hang an analog AC multimeter 
across the headphone leads and you can watch the "beat" on it.

Method 2 is an example of a very simple, test equipment-free mechanism 
that can achieve a really amazing frequency accuracy for your K3.  I 
used the terms "cycle" and "cps" in this because Hz hadn't been invented 
in the ancient era I was drawing my example from, and the term "zero 
beat" that originated from it can be both a verb phrase or a noun phrase.

I hope this clears up any misunderstandings I might have left about REF 
CAL Method 2.

73,

Fred K6DGW
Auburn CA

On 3/28/2011 7:41 PM, Scott Ellington wrote:
> This brings up an interesting point, though it doesn't affect the method at all.  The "beat" Fred refers to results from adding of the sidetone to the signal tone:  When they happen to be in phase, the volume goes up 6 dB, when they are exactly out of phase they cancel, so you hear the volume go up and down.  It is a completely linear process.
>