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Date: Mon, 20 Feb 2012 19:00:47 +0000
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From: Andy Talbot <andy.g4jnt@gmail.com>
To: ukmicrowaves@yahoogroups.com, rsgb_lf_group@blacksheep.org, 
	uk_beacons@yahoogroups.com
Subject: LF: Measurements on 10MHz references
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In the file    http://www.g4jnt.com/DownLoad/10MHz_ReferenceSpurii.pdf
are plots of the 10MHz outputs from several 10MHz references and
oscillators.
They include four GPSDOs of varying types, an HP5061 Caesium standard, an
oldish high quality TCXO recovered from a 1980's vintage STL comms
receiver, and my long in the tooth MSF frequency reference using a Toyocom
OCXO.
This latter, and the Cs standard, both generate 5MHz which was doubled for
these measurements using a full-wave rectifier doubler.

All plots were made using an SDR-IQ on the same settings: 0.37Hz FFT bin at
spans of 10kHz and 100kHz with 4 times averaging.  The final two
measurements on the two Simple GPSDOs were made by G0API using his SDR-IQ
with the same setup as mine.   For all plots, signal level / attenuation
were adjusted to be as close to full scale as possible without overload.

Some artefacts at the -100dBc to -110dBc region seem to be in common across
several plots, and I suspect these are locally generated or due to the
SDR-IQ.   However, there are enough and sufficient differences to see that
some sources are definltely better than others, and that the cheaper cost
conditioners do allow spurious signals onto the output.

My own ZAZ GPSDO, the second set of plots, originally showed unstable
sidebands at 650Hz which I realised were coming from an LCD backlight
inverter.  With this removed, it is now shown to be one of the better
sources - but with the high spec TCXO that was recovered from the old Decca
Navigator chain, berhaps not too surprising.

Teh second ZAZ plot, using the modern Morion OCXO is the cleanest in terms
of spuriou, although the phase noise of that oscillator is higher than many
of the others.   This is, I believe, characteristic of that OCXO which was
used originally mainly as a a timing unit, specifically  for its fast warm
up and low retrace errors rather than for its noise performance.


Andy
www.g4jnt.com

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<div>In the file=A0=A0=A0 <a href=3D"http://www.g4jnt.com/DownLoad/10MHz_Re=
ferenceSpurii.pdf">http://www.g4jnt.com/DownLoad/10MHz_ReferenceSpurii.pdf<=
/a>=A0=A0=A0 are plots of the 10MHz outputs from several 10MHz references a=
nd oscillators.=A0=A0 </div>

<div>They include=A0four GPSDOs of varying types, an HP5061 Caesium standar=
d, an oldish high quality TCXO recovered from a 1980&#39;s vintage STL comm=
s receiver, and my long in the tooth MSF frequency reference using a Toyoco=
m OCXO.=A0 <br>
This latter,=A0and the Cs standard, both generate 5MHz which was doubled fo=
r these measurements using a full-wave rectifier doubler.</div>
<div>=A0</div>
<div>All plots were made using an SDR-IQ on the same settings: 0.37Hz FFT b=
in at spans of 10kHz and 100kHz with 4 times averaging.=A0 The final two me=
asurements on the two Simple GPSDOs were made by G0API using his SDR-IQ wit=
h the same setup as mine.=A0=A0 For all plots, signal level / attenuation w=
ere adjusted to be as close to full scale as possible without overload.</di=
v>

<div>=A0</div>
<div>Some artefacts at the -100dBc to -110dBc region seem to be in common a=
cross several plots, and I suspect these are locally generated or due to th=
e SDR-IQ.=A0=A0 However, there are enough and sufficient differences to see=
 that some sources are definltely better than others, and that the cheaper =
cost conditioners do allow spurious signals onto the output.</div>

<div>=A0</div>
<div>My own ZAZ GPSDO, the second set of plots, originally showed unstable =
sidebands at 650Hz=A0which I realised were coming from an LCD backlight inv=
erter.=A0 With this removed, it is now shown to be one of the better source=
s - but with the high spec TCXO that was recovered from the old Decca Navig=
ator chain, berhaps not too surprising.=A0=A0</div>

<div>=A0</div>
<div>Teh second ZAZ plot, using the modern Morion OCXO is the cleanest in t=
erms of spuriou, although the phase noise of that oscillator is higher than=
 many of the others.=A0=A0 This is, I believe, characteristic of that OCXO =
which was used originally mainly as a a timing unit, specifically =A0for it=
s fast warm up and low retrace errors rather than for its noise performance=
.</div>

<div>=A0</div>
<div>=A0</div>
<div>Andy</div>
<div><a href=3D"http://www.g4jnt.com/">www.g4jnt.com</a></div>
<div>=A0</div>

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