Hi Mark looking at the M15m article where the design seems to stem from suggests that the oscillator is NOT opertaing on 150 or 200 MHz but in fact 40 to 50 Mhz with a cheap crystal and the LC collector circuit is selecting the the 3rd or 5th harmonic (not overtone a common mis-apprehension) The pulsing is just an RC in the base bias where the high value of R wont allow the circuit to oscillate hence it takes no current until the C is charged up.
My thought is a 200MHz overtone crystal could cost you $60, whereas a 50MHz 3rd OT will probably cost $20 and a cheap computer grade $2. The big difficulty will be getting cheap crystals on the right or anyway different enough frequencies. Crystals removed in rechannelling older 2-way radios may be a better source. I have hunders of these.....unfortunately I am in the UK. Alan G3NYK ----- Original Message ----- From: "Mark Sims" <hol...@hotmail.com> To: <time-nuts@febo.com> Sent: Friday, October 01, 2010 10:18 PM Subject: [time-nuts] Small quantity custom crystals This type of circuit is NOT a free running oscillator. It is a type of blocking oscillator that generates a short, high powered ping every second or two. It is designed to be able to extract every bit of power out of the battery. It can run for over a month off of a couple of button cells, yet generate a signal detectable over a mile away while it is laying flat on the ground. The allowable frequency bands are at 216, 217, and 219 Mhz. Each unit must be on its own freq, hence the need for one-off custom crystals. Yes, it is a weird circuit and depends upon all sorts of unspecified parameters. The components have to be hand selected and matched. This is the price one has to pay for this sort of operation. --------------------------------------- -Build a free running Colpitts oscillator and get it tuned to the frequency you want. Then, insert the crystal in series with theemitter. _______________________________________________ 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. _______________________________________________ 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.