Joe and all interested in the EXREF:
OK ... but most will not measure the 49.380 TCXO
directly*. *though REF CAL displays this.
What I think most want to know is how accurate their operating
frequency will be. I performed rigorous measurements as beta tester
of the EXREF (unfortunately my website was hacked a couple years ago
and I did not recover the beta-testing data page).
First one needs to realize that the TCXO establishes the basic
stability, so choosing the TCXO-3 over the TCXO-1 will provide better
stability and accuracy (these are two different things). I bought
the TCXO-3 with my initial K3/10 purchase so the rest of what I say
is with the better TCXO-3 installed (if frequency is important then
that is first thing I recommend updating).
Mostly, I use 28-MHz as a testing frequency since it is my VHF
transverter IF. On 28-MHz with only the TCXO-3, I see 14-Hz
inaccuracy. This 14/28000000 = 0.5 ppm (I think this is better than
Elecraft specs the TCXO-3). Adding the EXREF I see 2-Hz which is
"about" 0.1ppm. Measurements on 50-MHz are proportional. I see 3-4
Hz accuracy using the EXREF.
So going lower to 10-MHz I measure 1-Hz or less inaccuracy. Due to
the slow drift of the TCXO's, stability is same as accuracy (or maybe
better). So all ham bands lower than 10-MHz show less than 1-Hz
(basically I measure zero error).
Read below for optional background in my measurements-----------
I am measuring with a high-end mw counter able to count up to 26-GHz
and has an internal TCXO reference or can take an external 10-MHz
reference. I also have a LPRO Rubidium source which is rated +/- 5
E-11 stability. I find measurements using either the counter
internal TCXO or the Rb source are identical when measuring under
50-MHz signals (speaks well for that TCXO). I have to wait at least
30-minutes for complete warm-up stabilizing of the Rb source so
usually for normal frequency checks I just run the counter with internal TCXO.
MY station 10-MHz standard is a Russian surplus MV62 Morion OCXO spec
+/-5 E-12 (note it is more stable than my Rb). But the OCXO must be
calibrated as it is voltage tuned. I use the counter/Rb for
that. Long-term (measured in months) stability of my OCXO is only
+/-5 E-5 so I figure that I have to check the OCXO against the Rb
about twice/year (never been more than 1-Hz off in 3-years running).
The counter can only count to 1-Hz so measuring less than a Hz is not
possible. There are sw to make such but I have not gone there (yet).
I build transverters up to 10-GHz which use PLL LO's which actually
lock to the 10-MHz reference. I have noted that I can adjust my OCXO
when measuring 10,224.000,000 MHz to bring it closer to 10-MHz
because any sub-Hz error is multiplied in the mw LO multiplier
chain. Something I cannot do if directly measuring the 10-MHz
reference. Of course this is "nit picking" for setting the OCXO for
use on HF/6m with the K3EXREF.
One caveat in using a Rubidium full time as reference. They have a
finite life-span and more expensive (and probably harder to find once
one fails). So I only run my Rb for high accuracy checks and "lock"
for daily use to my $45 or $25 OCXO. My OCXO runs 24/7 from a 17AH
battery which is float-charged from a good 12v PS.
73, Ed - KL7UW
Date: Fri, 11 Mar 2016 13:25:54 -0500
From: "Joe Subich, W4TV" <[email protected]>
To: [email protected]
Subject: Re: [Elecraft] 10 MHz external reference - GPSDO
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8; format=flowed
> While locked to the external source, the K3?s reference
> oscillator frequency is maintained within 2 Hz.
The K3's reference oscillator is 49.380 MHz (+/-) not 10 MHz.
The K3EXTREF uses the external 10 MHz signal to gate a counter
which counts the reference. That count is then used to adjust
the reference frequency. Maintaining the 49.380 MHz reference
+/- 2Hz is on the order
of 0.04 ppm.
73,
... Joe, W4TV
73, Ed - KL7UW
http://www.kl7uw.com
"Kits made by KL7UW"
Dubus Mag business:
[email protected]
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