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Clean VHF tx schematics needed
I recently brewed up a small portable NBFM tranceiver for the local
ham group. Smallness and low cost were a requirement. My initial design which is working well is based on an 18MHz crystal that i multiply in balanced doublers three times over to 144MHz (using two transistors in push-pull at each stage) followed by a 500mW 2N3866 PA. I have found that without a high bandwidth oscilloscope (I used a tek 465) it is impossible to correctly align the tx. I am now considering switching to a scheme where i can run a VCO at 144MHz directly and lock it to a lower fundamental crystal. i can do this by: a) injection locking the VCO with the a crystal oscillator. I have seen almost no use of this method (EMRFD just mentions it in one line) in amateur literature. my last post on this topic went unanswered last week. b) using a simple first order PLL. is there a way to simplify this? the cost of a PLL IC or even an SBL mixer would be too high. c) use an overtone directly on 144MHz (9th overtone in a butler config) and phase modulate its output. Any pointers to a phase modulator operating at VHF? - farhan |
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