Mike Feher wrote:
I sure do agree, that with very low data rate systems it is significant. In fact, when David Allan & Fred Walls came up with the proposal of using this measurement as an FOM for oscillators over 30 years ago, digital communication rates were slow, and, the measurement was a good one. Due to the filtering process within ADEV by collecting and integrating a large number of samples, has a filtering effect of its own. Therefore, it can, and will, miss the fact that there may be instantaneous phase transitions that could cause havoc with high data rates and higher order PSK modulation schemes. So, again, I apologize, as I should have mentioned higher data rates. However, you must admit that your application, while extremely critical, is in the minority. I like to use the example of something like DirecTV. Here, they use a down-converter that utilizes a free running DRO, that is ridiculously noisy, and, varies all over in frequency, especially over the temperature ranges it subjected to. In spite of all of that, one gets a perfect pictures. Regards - Mike
no apologies necessary.. After all, I spend a small, but significant, amount of time explaining why we'd care about such things, since we are in the distinct minority of the radio comm world (trying to write nice comments on failed SBIR proposal evaluations to explain why they missed the big picture)
And, on the one hand, it's frustrating being the orphan child of the RF user community: you can't get off the shelf test equipment. On the other hand, it's cool, because then you have to *build* your test equipment.
To the Ku-band downconverters.. They're pretty crummy (but have a decent SNR to work with).. however, I've seen that there are two kinds.. a vanilla LNB and ones described as "crystal locked"... both are cheap ($20-30 for the former, maybe twice that for the latter)... what's the difference? And, getting into time-nuts territory here, where's the reference for the "locked" variety coming from? Up the coax? inside the LNB? And, can it be retrofitted from a much quieter oscillator? I was thinking that one could build a radio camera with a small array of Ku-band dishes, if you could lock all the receivers together. They *are* pretty low noise (20-30K)
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