Adding external clock to RTL SDR

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Adding external clock to RTL SDR

Post by SignalProcessor2 » Wed Feb 24, 2021 3:33 am

I would like to use the RTL SDR v3 in direct sampling mode with a high performance external reference clock, such as from a rubidium frequency source. As such, I also dont need to clock the R820T2 since I won't be using it.

I understand the RTL2832U requires a 28.8 MHz clock input. However, as there is no data sheet for the RTL2832U, what is the required clock input signal? I also dont have a schematic for the board. I would need to know:

-Differential or single ended
-Sine or square wave
-Input impedance
-Input pins and locations

Has somebody figured this out already or is there any documentation available? Otherwise, I can break out the microscope and Oscilloscope and try to figure it out.

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Re: Adding external clock to RTL SDR

Post by ckoval7 » Wed Feb 24, 2021 12:34 pm ... asheet.pdf

Page 7 of that guide should point you in the right direction.

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Joined: Wed Feb 24, 2021 1:47 pm

Re: Adding external clock to RTL SDR

Post by FromDC2Daylight » Wed Feb 24, 2021 1:55 pm

Using a Rb as the frequency source directly may be problematic as an RF clock input. The stability/accuracy of atomic clocks are far superior than quartz oscillators; however, they are notorious for poor phase noise performance. The best option would be to use a Rb source that is phase locked to a low noise OCXO as a clean up oscillator.

Depending on what exactly you are trying to do, a good OCXO by itself may be a better choice than a stand alone atomic clock.


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