Hi Don,
I can think of two ways to get an accurate digital frequency readout.
One way is to sample the LO or combination of LOs with a counter. The
other way is to control the LO (or LOs) with a digital PLL system. I
don't know all the details of a Century 22, so I cannot tell you exactly
how to do it. I'm pretty sure that you're not going to turn it into a
PLL rig, so the only way you'll get a digital readout is to sample the
local oscillator with a frequency counter.
If it is a direct conversion rig, then just sampling the LO input to the
first (and only) mixer with a frequency counter will give you a
frequency indication of the receiver zero beat frequency, as accurate as
the timebase reference used by the counter. If the rig has a BFO, then
it could be more complicated. You might have to count both the LO and
the BFO. Or you could or assume the BFO frequency is fixed and stable (a
reasonable assumption if it is a crystal oscillator), and preload that
number into the counter. Or do the math yourself from the number
displayed by the counter. In any case, I don't see how you can get a
digital frequency display without a sample of an oscillator. If you just
want to know your transmit frequency, put a sense antenna on your
counter. That is still sampling the PTO, even if not connected to it.
What is your objection to sampling the PTO?
DE N6KB
Don Rasmussen wrote:
Hi Guys,
I am considering changing the tuning indicator on my
Century 22 from the dial string to a small frequency
counter display. Can anyone suggest a method of
getting a signal sample, other than sampling the PTO
itself? I am not a EE but I can solder and follow
instructions well. ;-)
http://www.norcalqrp.org/fcc1.htm
Thanks,
Don Rasmussen Wb8yqj/6
Carlsbad, Ca.
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