[time-nuts] getting a grip on 10811 drift (beginner-ishquestion)

WarrenS warrensjmail-one at yahoo.com
Sat Nov 10 05:26:28 UTC 2012


Chris

HP 10811 can't drift that much that fast unless something is near broken, or 
being connected wrong like gnds or PS voltage.
Check the operation of the oven. It must be close and sort of working 
otherwise it would not be on freq as close as it is, but maybe it is 
drifting.
The other thing to check is what it is being compared to.  Are you sure it 
is the 10811 drifting and not your comparison reference?
Also Triple check to make sure the input to the EFC is not causing a problem 
the way you are using it by
grounding the EFC and count the cycle time for a beat freq.
If the freq is close to your reference, Adjust the 10811 to get a beat freq 
between the two 10 MHz signals or use a scope and Sync on the reference osc 
and time the drift rate of the 10811 osc a few times a day to see if the 
drift rate is changing.
A position change on the scope of 1ns /sec = 1e-9 freq offset,   1ns /10 sec 
is 1e-10, etc.

If all you have for comparison is a 1 pps from an unknown if working GPS's 
1pps, then sounds like it is time to get something else to break the tie to 
see which is really broken.
With the high freq drift rate of >> 1Hz that you are seeing,  you could use 
a wwv receiver.

ws

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[time-nuts] getting a grip on 10811 drift (beginner-ishquestion)
Chris Howard
Fri Nov 9 21:53:39 UTC 2012

My perpetually drifting 10811 pretty quickly made it to the negative
voltage rail on the control voltage.

I was looking at the oscillator output with an O-scope and it looked
pretty nasty.  My equipment is not so hot, so I first chalked that
up to bad probes.  But I did some google work on that and found an
old time-nuts message thread about the 10811 looking bad if the
output impedance is bad.

The VE2ZAZ board has provision for a 50 ohm resistor on the oscillator
output.  I have one on the board but it is a little-bitty thing,
maybe 1/8th of a watt?  Something I probably got from the guts of a VCR
or whatnot.  Hmm.  So I put in a 1/4 watt 50 ohm resistor (like
the parts list called for).  My working hypothesis is that the small
resistor was changing impedance due to heat.

I have reset the control voltage to center value and got the coarse
trimmer all beautifully centered.  It's been running for about a day
and I am hopeful that I've made a difference.  So far so good.

While I was interrupting the flow of 10 Mhz, I also mapped out the
control voltage and corresponding digital control value and an
approximate frequency.

You EE guys are probably snickering and will want to
tear the epaulettes off my time-nuts coat and break my sword.
What can I say. 




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