[ARDF] Piccon mods

[Jay Hennigan]

On Mon, 14 Nov 2005, Kenneth E. Harker wrote:

> I've only modified one piccon so far.

It would be interesting to modify the rest and see how well they track.
I think I would do this before trying to tweak for absolute accuracy
against a standard clock.

> The ceramic resonator is marked as 3.58 whereas the crystal is
> 3.579545 MHz.

Well, the ceramic resonator probably isn't precise enough to justify
any more significant digits.  And technically it should be 3.57954545
but who is counting?  Crystals/resonators on this frequency are plentiful
and cheap because they're used by the millions in TV sets.  In this
application they don't need to be all that precise because the oscillator
re-syncs them about 15734.26573 times a second, more or less.

> I suppose I should look at the circuit for the "old style" piccons which
> also used 3.579545 MHz crystals and see what they used.

They used a different chip that was set up for series-resonance with
a 360 degree phase shift, but the most common crystals are 18 to 20 pF
parallel so the designer may have tweaked the divisor to match what a
18 pF parallel designed crystal was actually generating in series mode.

> 3.4       The maximum deviation of the transmitting periods is FIVE SECONDS
> against the official time during the whole competition. The maximum
> transmitting overlap of two transmitters is FIVE SECONDS.

Well, you could always have the official time generated by a PicCon,
but that makes it pretty compelling that you need more accuracy.

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Jay Hennigan - CCIE #7880 - Network Administration - jay at west.net
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