[time-nuts] Small quantity custom crystals

[Alan Melia]

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" <holrum at hotmail.com>
To: <time-nuts at 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.
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