Cobra 2000 Crystal

[43Echo695]

I need to source an 11.325 MHz crystal for my Cobra 2000.

It's part# X3 QX-086, 11.325 MHz in the SAMS manual, but that's all it tells me.

I can have one cut locally as a one-off, but they are wanting all sorts of data like ESR,
f stability, calibration tolerance, load capacitance, shunt capacitance, storage/op temperature
range etc etc., and have probably never heard of a Cobra 2000 before.

Barkett Electronics have them, but don't ship outside the USA.

There are 2 ebay sellers, which can be easily found, who are selling lots and will ship to 43 division.
But they appear to be smaller type 49 holders, rather than the original type 51.

Anyone with experience of these? Any significance in the 11.3258 MHz?

The 2nd picture shows where it goes on the board using the outer 2 holes
for the leads.

Are the 2 inner holes there to accept the smaller type holder?

Radio is in storage right now, so can't see the solder side of the board.

Hope these pics post OK.

Thanks & 73's



View attachment 58865

 

[nomadradio]

The pc board will indeed accept either large or small crystals in that spot.

The 11.3258 MHz frequency gets tripled. The third harmonic gets selected by L21 coming from TR29.

That harmonic, 33.975, plus or minus clarifier range gets mixed with the approx 35 MHz VCO frequency in TR20. That difference between the two frequencies is what feeds into pin 17 of the 8719 PLL chip. The primitive chip transistors inside it weren't fast enough to divide the 35 MHz VCO frequency directly. The difference frequency for channel 1 is 780 kHz, and for channel 40 is 1.23 MHz. The binary inputs for the PLL circuit's divider are not 78 to 123, but 14 to 59. The chip adds 64 to the binary input on the chip's input pins.

And if none of this makes much sense, I'd recommend Lou Franklin's "PLL Data Book", or his "Screwdriver Expert's Guide".

http://www.cbcintl.com

73