Quote:
Originally Posted by newlite4
Just wondered if anyone has attempted to couple a frequency meter to the tuned circuit to act as a back-up until a cord replacement is carried out, maybe even becoming a permanent add-on.
Neil
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There are plenty of frequency counters available with offset options for the IF frequency. I have added frequency counters to most of my coms radios, Eddystone EC-10 and other radios like the ZC1.
Transistor radios require a different approach, those usually need a buffer amplifier if you want to ensure there is zero detectable pull on the the radio's L/O when the counter is attached, for those I even went as far as optical isolation which was better than any multi-stage transistor or fet buffer.(the acid test is to short out the signal at the output connector and see if there is a detectable effect on the L/O frequency)
However, there is a trick that you can use to extract the L/O signal from a valve set, where you do not require to add an active device or buffer amplifier.
It produces only a tiny near fixed offset in the L/O frequency which is easily tweaked out if needed. It simply involves using a very low value coupling capacitor and the capacitance of coaxial cable to form a capacitive divider. As the signal amplitude then is low, the counter may require a broadband amp at it input (I use monolithic amp IC's for that usually). The method applied to extracting the L/O out of a ZC1 radio is described on page 70 of this article:
http://worldphaco.com/uploads/ZC1_MK...R_SUPPLIES.pdf
In this case the signal was sent out a pre-existing connector on the front panel to avoid drilling any new holes.