Serial Data Quality Comparator Ideas

[Joe Leikhim]

I am looking at making a simple device to measure signal quality of four 
identical data streams that are arriving on different varying radio 
paths and then qualitatively select the best one.

My thought is to use a simple 567 phase lock loop tuned to the baseband 
frequency of the data.

Example for 16 Kbps, tune VCO to 8 KHz. If the incoming signal at pin 3 
contains significant 8 KHz tone, the 567 would lock on and set a 
received signal indication at pin 8. I would then amplify the loop 
signal at pin 2 and detect the level of instability (noise and jitter) .

There would be four of these PLL circuits and another circuit would 
select among the four, the ones with a received signal and then the one 
with the lowest S/N at the loop.

Has anyone seen this approach in practice? Any flaws to this approach? I 
imagine I will have to minimize the loop filtering at pin 2 to derive 
the results I wish. But since the data will be impressed on the signal, 
I am not sure how this will affect the measurement. Maybe I will need a 
high pass filter ?

Thoughts. If I am reinventing the wheel, please let me know!

This is to be a device, so using test equipment is not the solution.

Thanks

-- 
Joe Leikhim