[R-390] VFO End points

[Roger Ruszkowski]

Gordon,
 
Three different adjustment on the VFO.
 
One is in the Oldham coupler to get the Gears, dial and VFO together.
 
Second is an end point band spread adjustment to get the VFO to span 1 meg over 10 turns exactly
 
Third is the  track inside the VFO can. It's a bit tedious. Unless its a cosmos in which case it's still a bit tedious.
 
As you find your  390A zero beats at +003  and at -997 so it is 3 high on one end and 3 low one the other. It is pretty
close to dead on at the 500 Mark.
 
You need to do the end point adjust to get your band spread back to 1 meg over 10 turns
A counter works best. You can do it on the calibration tones.
 
After you get the band spread reset, you will then need to reset the zero on the
Oldham coupler as you reinstall the VFO.
 
Start in the Y2K manual at 6.2.16 End point Adjustment.

A small screwdriver and a couple tries.
If you start the right way it goes quickly.
Changing the spread will move both end points.
Do not try to hold the start stop point.
Make an adjustment,
Set one end to zero against the counter or the cal tone.
Make a tick mark across the coupler face and the VFO face.
Dial off ten turns exact. 
Listen to how close it is.
Go back ten turns 
Make another adjustment and start over.
You can get down to well under a 100 hertz total end to end error.

If you run out of adjustment, before you get exact, STOP
Do not force the adjustment.

You can open the VFO further, and take a turn off the trim coil.
Read about this in the Pearls if you need to go this route.


 
If you have no counter, and need to do this against the cal tones, post an e-mail I will
write it up here so we can get it saved in the archives again.

Roger AI4NI