[time-nuts] OCXO Adjustment Question

Alan Melia alan.melia at btinternet.com
Wed May 8 07:46:34 EDT 2013


I use this method too, but I also find it little use trying to get the 
internal reference down to the last squeak in 10^11 on this kind of kit. It 
will not hold the setting for vey long and it takes ages to get the 
adjustment spot on. I get as close as I can easily.....then allow the 
unknown to stabilise and do an estimate of the error and stick a label with 
thay value on the front until the next check is required  eg "2 in 10^9 high 
6thApr13" ......would not suit an avid "time-nut" but then the equipment is 
often barely "time-nut quality" :-))

Alan G3NYK

.
----- Original Message ----- 
From: "Bill Riches" <bill.riches at verizon.net>
To: "'Discussion of precise time and frequency measurement'" 
<time-nuts at febo.com>
Sent: Wednesday, May 08, 2013 11:52 AM
Subject: Re: [time-nuts] OCXO Adjustment Question


> This is the method I use for my 5110. There are two 10 mhz outputs on the
> osc - you can unplug one of the plugs and use a 10x probe there. My unit
> will hold a couple  of parts in
> 10-8 for months.
>
> 73,
>
> Bill, WA2DVU
> Cape May, NJ
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of J. L. Trantham
> Sent: Tuesday, May 07, 2013 11:52 PM
> To: 'Discussion of precise time and frequency measurement'
> Subject: Re: [time-nuts] OCXO Adjustment Question
>
> Fred,
>
> What I do is to apply the GPSDO to the trigger input of a scope and the
> output of the OCXO to be adjusted to the vertical input of the scope.  Set
> the time base to something line 100 nSec or faster and watch the output of
> the OCXO after it has warmed up for 30 minutes or so.
>
> This is an option only if you have an output from the OCXO you can watch.
> If no output, try a x10 probe attached to a 10 MHz connection from the 
> OCXO
> inside the monitor.  However, be careful that the probe does not 'load' 
> the
> OCXO and shift the frequency.
>
> Adjust the OCXO for a stable display, not drifting left or right.
>
> If the sine wave (or square wave) is moving to the left, the OCXO is high 
> in
> frequency.  If it is moving to the right, the OCXO is low in frequency. 
> If
> stable, it is matched to the GPSDO.  This is useful as long as the OCXO 
> and
> GPSDO are within a few Hz of each other.  The amount of time it takes for
> the display to shift 1 cycle tells you how close the OCXO is to the GPSDO.
>
> For instance, if it takes 10 seconds for the display to shift one cycle,
> 100,000,000 +/- 1 cycles went by in that 10 seconds or 1 part in 10E9 if I
> have my math correct.
>
> Joe
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Frederick Bray
> Sent: Tuesday, May 07, 2013 9:25 PM
> To: Discussion of precise time and frequency measurement
> Subject: [time-nuts] OCXO Adjustment Question
>
> This might be slightly off-topic, but probably there is a time-nut who 
> knows
> the answer.
>
> I am trying to adjust the 10 MHz OCXO in a Cushman 5110 service monitor. 
> I
> am using a frequency counter driven by a GPSDO.  Perhaps someone can 
> educate
> me about a couple problems I am encountering.
>
> I tried making small incremental adjustments but after I am done, the
> frequency drifts several Hz and then re-stabilizes at a new value.  When I
> make further adjustments, I notice strange behavior. For example, if I
> initially turned the adjustment clockwise to increase the frequency, it 
> will
> now decrease if I turn it clockwise and increase if I turn it
> counter-clockwise.  On the next adjustment, it will reverse again.
>
> Is there some correct procedure to adjust an OCXO?
>
> Many thanks for any suggestions.
>
> Fred Bray
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