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: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Ben Hofmann K1NT Sent: Wednesday, December 20, 2006 8:17 PM To: [email protected] 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: [email protected] 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 _______________________________________________ Elecraft mailing list Post to: [email protected] 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
