| 
				 Clean VHF tx schematics needed 
 
			
			I recently brewed up a small portable NBFM tranceiver for the localham 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
 
 |