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SDR crystal oscillator frequency

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Hi,

I am using a  R820T2 DVB-T SDR  (USB dongle from NooElec) and was wondering how I can measure the oscillation frequency (crystal) on the PCB.

I've hooked up an oscilloscope. Ran an FM receiver program using Gnu Radio. Then I connected the probe of the oscilloscope to the XTALO and connected ground.

However the program stops running when I measure and don't get any value.

Any suggestions would be great!

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Are you near anybody with a frequency counter? What is the impedance of the probe? What type of coupling does the probe have? How fast is the sweep on your scope, 10nSec?

Does the oscillator look like this? - https://www.digikey.com/product-detail/en/txc-corporation/9C-28.800MBBK-T/887-2449-2-ND/4475367  ---   28.8 MHz???

To read the exact frequency, find a 10 pF (smaller is better) capacitor and "hook" one end of the capacitor with your o-scope probe. Set the channel and trigger to AC coupled.

Now look at the PC board and next the crystal "Y1" find capacitors "C3" and "C2" near the edge of the board. Each capacitor has one pin tied to ground (the one towards the middle).

Move the capacitor on the scope probe to touch the one end of the C3 but don't touch the metal on the crystal can. Start by touching C3 the side away from capacitor C2 and adjust the trigger till you get a lock and measure the distance between peaks. Now try to back the probe away so the capacitor probe doesn't touch the pin but can still couple and try to read the peaks again. The act of touching the crystal pin will actually shift the frequency a little bit. I speculate the peaks will be slightly less than 35 nSec apart.

Good luck,

Joel - KD6W

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