Ian,
Two possibilities occur to me. First, detune the LO inductors L3, L4
and L5 a bit to give you 3 volts maximum at TP1 and see if it stabilizes.
Secondly, try adjusting L4 a bit. It may be that the adjustment of L4
puts the crystal right on the 'hairy' edge of oscillation which would
make the frequency unstable. The voltage at TP1 should remain between
1.7 and 3.0 volts.
73,
Don W3FPR
On 1/25/2013 3:40 AM, Ian Greenshields wrote:
The LO on my XV432 transverter seems to be very unstable. I think it's
something more than just temperature drift as the frequency will sometimes
jump by several kHz. It's almost as if the crystal is hunting between
different modes of oscillation.
Prodding & wiggling the components in the LO circuit doesn't point to any
obvious poor connection, although the crystal itself is sensitive to being
touched, or heated by a finger. The LO alignment voltage at TP1 peaks at
about 3.3V.
I don't have the temperature oven for the crystal, although I think it's a
requirement. But I'm concerned about the frequency jumping and a frequency
drift of almost 10kHz which I would not expect even of a non-temperature
controlled crystal oscillator.
Any thoughts or pointers as to what could be wrong?
TIA, Ian G4FSU
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