[time-nuts] HF frequency counting receiver

Graham / KE9H ke9h.graham at gmail.com
Mon Jun 20 12:34:04 EDT 2016


You can do it this way, but it requires you to totally understand the
mathematics and granularity of ALL of the frequency sources and
synthesizers in the superhet receiver.
And if there are any audio soundcards or sampling devices involved, the
specifications and origin of the sampling clocks.  If it is the USB clock
in your computer, you can be pretty much screwed right there.

These are generally not published by the manufacturers, so you will need a
friend at the manufacturer to provide you this information. Or be ready to
do a lot of reverse engineering.

The typical RF frequency measurement system for off-the-air measurement
only uses the superhet for signal reception, then adds a precision (GPSDO
derived) local oscillator/signal source for which you totally understand
the mathematics and granularity, because you built it yourself, and an
audio counter that allows you to measure the audio difference between the
signal to be measured, and the local precision reference that you inject.
In this system, the absolute frequency of the superhet receiver is a "don't
care".  You just want to measure the difference between the signal to be
measured and your local precision reference.

--- Graham


On Mon, Jun 20, 2016 at 9:51 AM, Nick Sayer via time-nuts <
time-nuts at febo.com> wrote:

> I'm considering taking a shot at the next ARRL frequency measurement
> contest.
> The assumption going in is that the signal is CW, with at least a half
> minute or so of just solid "on" at one point or another and that reception
> is reasonably good.
> I've got a good TIA and excellent references, but that's the easy part, it
> seems to me. It seems to me that what I really need to do is make a
> synthesized heterodyne receiver that can present an accurately tuned RF
> band pass - say, 10 kHz wide with the synthesizer set for
> 5 kHz steps - to the TIA, with some manually tunable high-pass and
> low-pass filtering to isolate the signal of interest. If the mixer got its
> LO from a synthesizer with a GPSDO reference, it seems to me that you could
> then measure the frequency of the signal of interest (now an audio
> frequency, so you can listen to it too) with the TIA (also getting the
> GPSDO reference) and then do simple math to arrive at the actual RF
> frequency.
> Anybody have any thoughts?
> Sent from my iPhone
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