[SADXA] Frequency Measurement Test

[Wes]

I was going to write a detailed report on my method, but didn't want to bore 
folks.  So in a nutshell, I use GPS derived signals to downconvert the unknown 
to an audio frequency (~600 Hz).

Then I rely on Spectrum Lab software's remarkable ability to interpolate FFT 
bins even on a noisy signal that is spread in frequency and amplitude.  I juggle 
the FFT window time (length) and sample rate to trade off acquisition time and 
FFT bin size.  Of course longer and narrower have better resolution but on noisy 
signals it's pointless. Generally, I was using about 16 sec and 60 mHz bins. 
Quite frankly, I'm astounded that I'm coming up with numbers that are so good, 
considering the signals involved.

As to your real questions about Doppler. etc. I can't really overcome it so I 
live with it and report what I measured.  Either my results have serendipitous 
bias in the right direction or the Doppler was "in the noise" no pun intended.  
My 20-meter daytime results were an order of magnitude more accurate than the 40 
and 80-meter ones from near sunset times.  In some cases, I averaged the averages.

Since I recorded the signals, I can revisit them if I become so motivated.

Wes  N7WS



On 8/15/2020 8:20 AM, Darrel Emerson wrote:
> Congratulations, Wes!
>    I'm impressed that you were able to overcome some of the ionospheric 
> Doppler shift.  For how long did you average measurements to get your final 
> results?  Any other tricks to reduce the impact of the ionosphere?
>
>        Cheers,
>                 Darrel, aa7fv.
>
>
> On 8/15/2020 8:03 AM, Wes wrote:
>> There are two "official" ARRL FMTs per year, but we frequency nuts clamor for 
>> more.  Hence Connie, K5CM, the reference station, has been doing unoffical 
>> ones more frequently.
>>
>> The last one was Thursday (MST) afternoon and evening.  I thought the bands 
>> were awful and even disconnected antennas between the two 80-meter runs 
>> because of lightning concerns. Nevertheless, the results were posted this 
>> morning (http://k5cm.com/aug%2013%202020%20fmt.htm) and I did quite well, 
>> coming in fifth in the parts-per-million metric.
>>
>> Wes  N7WS
>>
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