[time-nuts] HF frequency counting receiver

Bob Camp kb8tq at n1k.org
Mon Jun 20 15:52:24 EDT 2016


The cheaters way is to simply use a fully synthesized radio tied to a known 
reference frequency. Feed the output into one channel of a sound card. Feed 
the other channel of the sound card with a known frequency tone. Post process 
it to death with your choice of FFT programs. 

Another approach is to use a synthesized generator. Feed an appropriate level tone
into the antenna input of the radio through a combiner. Set it so that both it and
the FMT signal are inside your passband. Some care should be taken to see that
you do not radiate your test tone. 

If you are going to rig up something special … just do a SDR of some sort. The post processing
is all the same once it gets to audio. The noise and fading are such that there is 
essentially no way to directly read the frequency. That was true back when I was within 
ground wave for the transmissions. It’s even more true if you don’t live next door to them
RF wise. 


> On Jun 20, 2016, at 10:51 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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