[time-nuts] HF frequency counting receiver

[Dan Rae]

On 6/20/2016 11:18 AM, Mark Spencer wrote:
>   I am quite convinced that HF Doppler shift is a real issue at times.
>
Absolutely true Mark.  I spent some time looking at this way back when 
and it is quite possible to observe (in Southern Calfornia) transitory 
phase shifts on the 10 MHz signal from WWV of more than 360 degrees.  
Some times of day are worse than others.

In 2003, the last time I bothered with the FMT and then it was from a 
signal at the ARRL, i.e. right across the country from me, I was able to 
get within 0.1Hz using nothing more than a 1Hz tuning receiver with 
external reference and a 100 kHz IF output which I compared with another 
output from the Standard on an oscilloscope. But this did involve a lot 
of visual averaging and estimation on the 'scope as the apparent 
received frequency varied.   This was the usual method of measuring 
frequencies off air in the day.

Most more "modern" FMT approaches have been using sound cards, but I've 
no experience of these.

Whatever method is used once you have any ionospheric reflections then 
you will start to see phase shifts which will be what limits your accuracy.

Dan

ac6ao