Re: [time-nuts] FE-5680A's suitability for use as a 10 MHz reference for microwave transverters
Last week I noted that the FE-5680A's "barefoot" output was found to NOT
be a suitable 10 MHz reference for microwave transverters.
Specifically, I tested it on two different 10 GHz transverters and found
there to be objectionable levels of "grunge" on signals caused by
low-level phase modulation internal to the '5680A and at 10 GHz the
result of this phase modulation was a racket of audible and subaudible
noises on CW carriers that made it difficult to find zero beat! In
comparison, the 10 MHz outputs of the Z3801, Isotemp VCXO and LPRO-101
yielded results at 10 GHz that were quite clean. Related observations
were also made by N8UR in his web page comparing various units.
In order to clean up the output of the FE-5680A I did the obvious thing,
disciplining a homebrew VCXO to its output - details are found here:
http://www.ka7oei.com/10_MHz_Rubidium_FE-5680A.html
While the comparison frequency is fairly high (1.25 MHz) the loop gain
and bandwidth are quite low so it's pretty much the Butler oscillator
VCXO that determines the phase noise of the 10 MHz output and I can't
detect any audible artifacts from the '5680A at all. At the moment I
don't have the means of generating a "pristine" test signal at 10368
MHz, but from what I can determine, the resulting CW notes from the
transverter (being locked to the "regenerated" output of the the '5680A)
compared to the other 10 MHz sources sound the same. At some point I
hope to do a more-detailed analysis.
Had I a low-noise "canned" 10 MHz VCXO around, I'd have probably used
that rather than go through the hassle of building the oscillator, but
none of the 10 MHz VCXOs that I did have on hand produced as good a CW
note as the Butler built around a cheap microprocessor-type crystal. I
also had on hand some 10 MHz ovenized VCXOs which would have worked
fine, but not only were these too large to fit in the box, they would
have added even more current consumption to an already power-hungry
frequency source - an important consideration when operating from a battery!
There are, no doubt, a number of ways one could do this same thing, but
it's clear that this simple of a circuit will do an admirable job of
extracting the frequency stability of the FE-5680A without the
synthesis-related artifacts. Of course, the regenerated 10 MHz output
will have a degree of variable phase offset with respect to the '5680A's
"barefoot" 10 MHz output over varying conditions (such as temperature)
but when used only as a frequency reference these rather slow changes
are unimportant.
73,
Clint
KA7OEI
Clint a good read and a fine approach.
By accident I looked at the original filter schematic first and believe it
has an error for the first output amplifier. The 470 ohm resistors in the
wrong location.
Others on the list have mentioned the same thing about the 5680s output
being dirty. You have that fixed up nicely.
Regards
Paul
WB8TSL
On Mon, Feb 13, 2012 at 4:03 PM, C. Turner turner@ussc.com wrote:
Last week I noted that the FE-5680A's "barefoot" output was found to NOT
be a suitable 10 MHz reference for microwave transverters. Specifically, I
tested it on two different 10 GHz transverters and found there to be
objectionable levels of "grunge" on signals caused by low-level phase
modulation internal to the '5680A and at 10 GHz the result of this phase
modulation was a racket of audible and subaudible noises on CW carriers
that made it difficult to find zero beat! In comparison, the 10 MHz
outputs of the Z3801, Isotemp VCXO and LPRO-101 yielded results at 10 GHz
that were quite clean. Related observations were also made by N8UR in his
web page comparing various units.
In order to clean up the output of the FE-5680A I did the obvious thing,
disciplining a homebrew VCXO to its output - details are found here:
http://www.ka7oei.com/10_MHz_**Rubidium_FE-5680A.htmlhttp://www.ka7oei.com/10_MHz_Rubidium_FE-5680A.html
While the comparison frequency is fairly high (1.25 MHz) the loop gain and
bandwidth are quite low so it's pretty much the Butler oscillator VCXO that
determines the phase noise of the 10 MHz output and I can't detect any
audible artifacts from the '5680A at all. At the moment I don't have the
means of generating a "pristine" test signal at 10368 MHz, but from what I
can determine, the resulting CW notes from the transverter (being locked to
the "regenerated" output of the the '5680A) compared to the other 10 MHz
sources sound the same. At some point I hope to do a more-detailed
analysis.
Had I a low-noise "canned" 10 MHz VCXO around, I'd have probably used that
rather than go through the hassle of building the oscillator, but none of
the 10 MHz VCXOs that I did have on hand produced as good a CW note as
the Butler built around a cheap microprocessor-type crystal. I also had on
hand some 10 MHz ovenized VCXOs which would have worked fine, but not only
were these too large to fit in the box, they would have added even more
current consumption to an already power-hungry frequency source - an
important consideration when operating from a battery!
There are, no doubt, a number of ways one could do this same thing, but
it's clear that this simple of a circuit will do an admirable job of
extracting the frequency stability of the FE-5680A without the
synthesis-related artifacts. Of course, the regenerated 10 MHz output will
have a degree of variable phase offset with respect to the '5680A's
"barefoot" 10 MHz output over varying conditions (such as temperature) but
when used only as a frequency reference these rather slow changes are
unimportant.
73,
Clint
KA7OEI
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paul swed wrote:
Clint a good read and a fine approach.
If and only if the high phase noise pedestal exhibited by the buffer
amplifier that extends to offsets of a few hundred kHz or so isn't an issue.
The relatively low isolation between the 10MHz outputs may also be an issue.
By accident I looked at the original filter schematic first and believe it
has an error for the first output amplifier. The 470 ohm resistors in the
wrong location.
Others on the list have mentioned the same thing about the 5680s output
being dirty. You have that fixed up nicely.
Regards
Paul
WB8TSL
On Mon, Feb 13, 2012 at 4:03 PM, C. Turnerturner@ussc.com wrote:
Bruce
Nice job!!
Rob
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of C. Turner
Sent: 13 February 2012 21:03
To: time-nuts@febo.com
Subject: Re: [time-nuts] FE-5680A's suitability for use as a 10 MHz
reference for microwave transverters
Last week I noted that the FE-5680A's "barefoot" output was found to NOT be
a suitable 10 MHz reference for microwave transverters.
Specifically, I tested it on two different 10 GHz transverters and found
there to be objectionable levels of "grunge" on signals caused by low-level
phase modulation internal to the '5680A and at 10 GHz the result of this
phase modulation was a racket of audible and subaudible noises on CW
carriers that made it difficult to find zero beat! In comparison, the 10
MHz outputs of the Z3801, Isotemp VCXO and LPRO-101 yielded results at 10
GHz that were quite clean. Related observations were also made by N8UR in
his web page comparing various units.
In order to clean up the output of the FE-5680A I did the obvious thing,
disciplining a homebrew VCXO to its output - details are found here:
http://www.ka7oei.com/10_MHz_Rubidium_FE-5680A.html
While the comparison frequency is fairly high (1.25 MHz) the loop gain and
bandwidth are quite low so it's pretty much the Butler oscillator VCXO that
determines the phase noise of the 10 MHz output and I can't detect any
audible artifacts from the '5680A at all. At the moment I don't have the
means of generating a "pristine" test signal at 10368 MHz, but from what I
can determine, the resulting CW notes from the transverter (being locked to
the "regenerated" output of the the '5680A) compared to the other 10 MHz
sources sound the same. At some point I hope to do a more-detailed
analysis.
Had I a low-noise "canned" 10 MHz VCXO around, I'd have probably used that
rather than go through the hassle of building the oscillator, but none of
the 10 MHz VCXOs that I did have on hand produced as good a CW note as the
Butler built around a cheap microprocessor-type crystal. I also had on hand
some 10 MHz ovenized VCXOs which would have worked fine, but not only were
these too large to fit in the box, they would have added even more current
consumption to an already power-hungry frequency source - an important
consideration when operating from a battery!
There are, no doubt, a number of ways one could do this same thing, but it's
clear that this simple of a circuit will do an admirable job of extracting
the frequency stability of the FE-5680A without the synthesis-related
artifacts. Of course, the regenerated 10 MHz output will have a degree of
variable phase offset with respect to the '5680A's "barefoot" 10 MHz output
over varying conditions (such as temperature) but when used only as a
frequency reference these rather slow changes are unimportant.
73,
Clint
KA7OEI
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