I have had good results with the part if this circuit around T1. http://www.qsl.net/on7yd/minitx2.htm
Varying L1 selects the right overtone for basic operation. The collector circuit here has a coupled resonator tuned for the 144, but it will probably work equally well for 216. A cheap (fundamental) 24Mhz computer crystal operating at 72 MHz will get you there. Just alter the filter for 3 x 72 instead of 2 x 72. Note as someone else posted that the frequency at 72 may be tens of KHz higher than that. Each brand or even each individual crystal will vary here. You could also stick to the collector circuit from your tracker transmitter circuit if you want to keep things as small as possible. It worked down to 1.1V in bench tests with a MPSH10 transistor. Tuning the bias with R2 helps to optimize the power for the desired output frequency. More bias then necessary will only consume more battery power and not contribute to the output. Actually power output may be less. For more insight look here: http://www.wenzel.com/pdffiles1/pdfs/choose.pdf Cheers, Joop - pe1cqp _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.