Re: RSPDuo and SDRC


jdow
 

I knew somebody would ask that. You have to get into the design for frequency synthesizers to understand the effect. An example is the rtlsdr dongle synthesizer. It works on the basis of the average frequency being correct as it dithers between two "exact" settings. If you are simply listening there's no big problem. (Although SSB could sound "odd".) Two dongles set the same will still wander up and down with respect to each other enough to foul up efforts to perform RDF or nulling functions. There have been discussions of this on rtlsdr.com. Getting the dividers in the synthesizers in the same phase as each other takes some effort. Apparently when done, however, they have had success with techniques that require two receivers on two antennas that are tuned to EXACTLY the same frequency with no phase dither between them.

Was I clear enough, I hope. I want to be clear without wandering too far into the weeds.

{^_^}

On 20210722 10:31:11, Bob Dengler wrote:
At 7/22/2021 03:05 AM, you wrote:
If it has separate synthesizers then you can take it to the bank you will have synchronization problems for nulling applications and the like. For average listening it ought to be "Pluto level" good. {^_^} 
If the 2 synths are locked to the same reference, why would they drift w.r.t. each other?  Isn't that the definition of "phase locked"?

I can recall one instance where two commercial synthesizers locked to the same reference did drift w.r.t. each other over time, maybe 10° or so per minute.  But the outputs of both were multiplied up to ~500 GHz.

<O_O>

Bob NO6B 






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