What DC voltages (measured with a DVM) do you see on the pins of Q2 and Q3?
Brian.
Hi Brian,I agree with BigBoss but my concern is that Q3 has to be fully conductive before enough current can flow to start oscillation. The image is cut off on the right edge but my guess is the FET is a BS138 so it would need at least 2V on it's gate to ensure conduction and preferably would have a little more.
Brian.
It can be simulated in ADS or AWR but components' specifications and especially CR's equivalent circuit should be supplied.
Coaxial Resonators don't work below 1GHz, and I guess that this oscillator has been designed for sub-GHz frequencies. There is a mistake meseems.
-10 dBm what? Noise? Or discrete frequencies? In the latter case, how do you say it's not oscillating?For a good PCB; after testing and checking at C10 in a spectrum analyser; I roughly get -10dBm.
Hi,Hi,
Can you show us the PCB layout?
Klaus
Hi FvM,1. There are circuit details that I don't understand. If L4 isn't fitted, how is D50 biased?
2. What is the design state? Is the circuit newly designed and has never operated before? Or is it an existing product, but possibly defective?
3. To check the design, we would need complete specification, also resonator and varicap part numbers.
4. Why there are there multiple schematic copies, each which different part identifiers?
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Regarding transistor bias, it would be easy to determine Q2 Vce and Ic.
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-10 dBm what? Noise? Or discrete frequencies? In the latter case, how do you say it's not oscillating?
Hi Vfon,Replace the L12 100nH inductor with bigger value (e.g. 1uH) and the VCO will oscillate. But you have to pick-up the output signal from the emitter, not from the collector, as it is now.
Using LTspice I get steady oscillation arround 145 MHz, using the values and components in the picture attached. I don't know what coaxial resonator you chose, so I use a 100nH inductor instead.
Never use an inductor on the control line of the varicaps (L10 in your schematic), because its reactance varies with frequency. Use instead a high value resistor.
I see that this is a CW transmitter. It is a very bad idea to key the VCO stage, as you do now. Set the VCO in continous mode, and key Q6 or Q7, or both.
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