[TenTec] Century/22 tapping rx freq for digital counter

[Dr. Gerald N. Johnson]

There ought to be 6.5 in and 10 in. There will be 3.5, 6.5, 10, and 16.5 
on the chip output. The two mixer products, sum and difference, 3.5 and 
16.5 should be about equal strength and if the mixer is balanced 
properly the 6.5 and 10 should e 40 or 50 dB weaker. Probably there's 
not enough 3.5 and 16.5 for your counter to detect, and then there's the 
question of what will it count? It takes the bandpass filter to clean up 
the signal to just one of those for transmit. That multiple frequency 
signal should be on C20 and the anode of D1.

However this being a direct conversion receiver, its fairly sensitive to 
LO leakage and you don't want a probe and amplifier (up to volts for the 
counter) at the signal frequency. That will tend to block the receiver 
so you can't hear anything but really strong signals.

The counters made for receivers where they take separate inputs for 
crystal, pto, and BFO, and mix them or add and subtract the digital 
results would work, just you'd use no BFO signal. A general purpose 
counter won't work without the transmit bandpass filters and some gain 
stages.

73, Jerry, K0CQ

On 2/12/2011 9:04 AM, VE3XGB wrote:
> Hi all,
>
> I've got a digital freq counter and wanted to use it as a digital freq readout on my Century/22 but I can't seem to find a 'source' in the rig.  The circuit diagram shows the mixer as a UPC1037 (?) IC but mine has a MC1496P.
>
> Anyway I found the data sheet for the MC1496P double-balanced mixer and it would seem to suggest that pins 6 and 12 were the output but when on 80m I couldn't find a 3.5XX MHz signal on any pins.  I can see the 10.000 MHz band crystal output and I can see the 6.5 MHz PTO output (difference in the 3.5XX range) but nothing 3.5XXX
>
> Thanks for any suggestions
> _______________________________________________
> TenTec mailing list
> TenTec at contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
>