Joined: 12 March 2008
Location: DE
Posts: 1

Back to Top

Hello, I have to design a transceiver at 170MHz. I got an Evaluation Board and put on the VCO an external varactor diode (BBY53) to get this output frequency. My problem is, when I try to increase the TXPOWER from P1 to P2 the voltage on Pin 23 (LF) is going to zero and so the output frequency change. Then I changed the VCOCUR to the highest. After that it works. But then I changed from P2 to P3 and I have the same problem. Can you please help me what is to do that the Output frequency is constant at every TXPOWER mode? Thank you Armin

Joined: 1 January 2005
Location:
Posts: 86

Back to Top

Hello Armin,

Check the tuning voltage on pin 23. It is probably close to 0V. The VCO capacitance changes slightly with VCO current and output power. If it is close to the limit, it will loose lock with different settings. I can send you a schematic for my board which tunes 160-174MHz if you would like it.

jon@melexis.com