[Elecraft] 10M birdie and other assundries

[pc5m, Carel]

Hi Ben,

My assumption is that the birdie is due to mixing of the VCO with X-tal
frequencies. At certain a (VCO) frequency it will be such that this mixing
product will produce exactly the IF frequency--> a birdie is born. Of course
will this "certain" VCO frequency correspond with a RF frequency (the
frequency which is on the display of the K2).

Now we need to do some maths....:-)

So the calculation is as follows: 
(1) X*Fxtal + Y*Fvco = Fif  (never mind the + sign , minus is also taken
care for by the negative Y values).

Fxtal = KPA100 xtal freq
Fvco = K2 VCO freq
Fif = K2's IF (4.9136 MHz)
X and Y are integers from e.g -4 to + 4, i.e. -4,-3,-2, etc to +4 (number of
mixing products you would like to consider)

Also we do know that Fvco = Frx - Fif (minus will be a plus depending if you
are below or above 17 mtrs)
(2) Fvco = K2 VCO freq
Frx = K2 "displayed" freq
Fif = K2's IF  

With (1) and (2) we can solve this equation: 
(3) Frx = Fif + (Fif-X*Fxtal)/Y and (below 17 mtrs)
(4) Frx = -Fif + (Fif-X*Fxtal)/Y (above 17 mtrs)

This is basically what my spreadsheet is showing, it will loop through the
matrix of X and Y values, and calculates Frf depending on the chosen Fxtal
and (fixed) Fif. That is will show this matrix for every band and perform a
conditional format (red) for in band products. The other colors have been an
attempt to show that mixing products with a lower order of X and Y will be
stronger than those with larger numbers, although I did find any proof of
that (somethimes higher order mixing are even stronger than lower..)

And you are correct ! 15.873 would be perfect...

Would really appreciate if someone could take the time and verify above
paradigm.

Gl,

Carel, pc5m


-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Ben Hofmann K1NT
Sent: Wednesday, December 20, 2006 8:17 PM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] 10M birdie and other assundries

If PC5M's calculations are correct, and these birdies
are caused by mixing products of the 4.9136 MHz IF
crystals in the K2 and the 18.432 MHz bias supply
crystal in the KPA100, and assuming his spreadsheet
calculations are correct, it seems that a crystal at
15.8735 MHz (+ or - about 9.5 kHz) would not produce
mixing products in any US ham band (including 5.3305
through 5.4065 MHz for 60m).  Since this is not a
standard crystal frequency, I wonder what the cost
would be of a batch of custom crystals at this
frequency?  It seems that even within general
tolerances for calibration and temperature stability
for both values of crystals this should be feasible. 
Like I said, I don't know what the cost of a run of
custom crystals would be, but it may be something for
the folks at Elecraft to look into for future outgoing
KPA100's, and then those of us who wish, could
purchase one as a spare part to retrofit our existing
amps.  Another alternative would be a separate
individual purchasing a batch of custom crystals for
sale to Elecraft users.  Just a thought.  What do you
all think?

-Ben  K1NT
_______________________________________________
Elecraft mailing list
Post to: Elecraft at mailman.qth.net
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft    

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com