onsdag den 19. juni 2019

The GPSDO makes my LNB rock-stable

A consumer-type LNB for Ku-band can receive the QO-100 satellite transponder. A LNB with PLL-oscillator has an acceptable frequency stability after warm-up, but it still drifts. The reason is outdoor temperature changes and a simple oscillator using a cheap crystal.

Adding a GPSDO will greatly improve the frequency stability in the receive chain. The block diagram below shows how the GPSDO injects a clock signal into the LNB. The clock signal from the GPSDO has superior stability compared to the LNB oscillator. 

GPSDO generates a 25 MHz clock signal for the LNB.

I decided to buy a GPSDO developed by 4 danish radio amateurs. The project is named RFzero. The price of the RFzero board was less than 50% of the Leo Bodnar mini-GPSDO. Another advantage of the RFzero is the possibility of writing your own software using the Arduino IDE. The RFzero board is assembled, and only a few optional pins are soldered by the end-user.
The RFzero board.

I've mounted the RFzero board in an aluminium box. Power (5 V DC) is supplied via the USB interface. An external PSU can also power the board.

GPSDO front view.


GPSDO rear view.

GPSDO with lid removed.

Conclusion: Adding a GPSDO has greatly improved my receive chain. The Narrow-Band beacons are now rock-stable regardless of the LNB temperature. 

Vy 73 OZ1BXM Lars
My webpage: http://oz1bxm.dk/ 

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