On 25/07/12 22:18, Chuck Forsberg WA7KGX N2469R wrote:
How about a 10 MHz OCXO and a divide by two chip? Maybe an op-amp to
change and/or invert
the control voltage?
In the end that's exactly what I did.
Details on eevblog -
http://www.eevblog.com/forum/projects-designs-and-technical-stuff/rapco-1804m-repair-10mhz-conversionbodge-(-teardown)/
Found a 10MHz ocxo which seems to have very similar specs to the 10Mhz
1804Ms running without GPS and dropped that in.
There's a handy 22ohm damping resistor in the track which takes the 5MHz
round to the logic so lifting that allows one to insert a divide by two
bodge, leaving 10MHz at the rear BNC. Didn't have too many problems
achieving "fine" control for the oscillator - took about 24 hours,
although I did tweak the DAC output manually to be in the right ball
park - it needed quite a large shift & I wasn't sure whether the
firmware would make such a large correction, or take a very long time to
do it.
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