[time-nuts] Progress on the FE-5680A serial commands!

Bob Camp lists at rtty.us
Fri Jan 20 12:25:51 EST 2012


Hi

Based on the frequency plot of your unit, it swings about 35 Hz high and
about 170 Hz low as it sweeps. You could bump the trimmer on the VCXO and
move it up by about 70 Hz or so to keep it from running out of range. Since
the VCXO is trending down in frequency as it warms up, this may be needed
sooner rather than later ...

Bob 

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of John Beale
Sent: Friday, January 20, 2012 1:29 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Progress on the FE-5680A serial commands!

On 1/19/2012 9:52 PM, Scott Newell wrote:
> http://n5tnl.com/time/fe-5680a/graphs/fe5680_2_ch3.png
> http://n5tnl.com/time/fe-5680a/graphs/fe5680_2_ch4.png
> This assumes that the reply from the undoc command 0x5a is the raw counts
> from the 4 channel 12 bit ADC. I think channel 3 is a temp sensor. What
> would channel 4 be? Photodiode output?

Great detective work Scott! I'll bet Channel 4 is voltage to the VCXO. It 
is driven up and down at startup searching for the lock, then it settles 
down, but the oscillator components are also affected by temperature so the 
VCO voltage would logically track the temperature too.  At least it seems a 
reasonable theory.

For example, look at this plot of the 10 MHz output frequency after 
powerup. It has a similar look to your Channel 4, except for the post-lock 
drift.

https://plus.google.com/photos/109928236040342205185/albums/5680473650837554
113/5681715799377076466?banner=pwa

-John Beale

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