If you just need a 10-MHz reference then you do not need a GPSDO. A
simple surplus OCXO (oven controlled xtal oscillator) off e-bay will
suffice. I bought a one for about $45 initially (Morion). Since
then I bought two sine-wave OCXO for $25. You do need to supply very
clean 12v dc for most of these and a stable bias 0-5v for tuning the
OCXO to 10.000,000 MHz.
Short term stability is 5 E-12 which will do fine with the
K3EXREF. The TCXO is the limiting factor for frequency in the K3 so
really no need for GPS accuracy. If you are feeding a PLL system
then the GPSDO will be better.
I use a LM7805 to 100K 15 turn pot to supply the tuning bias. Adding
a medium value electrolytic cap before the OCXO is extra insurance to
eliminate any ac ripple or noise from modulating the OCXO. One could
also float charge a battery to feed the OCXO which also damps out any
ac. Why I mention this is I was using a 1.5A RS wall wart charger
initially until I was told I had 120-Hz spurs on my signal. There
was about 0.3vac ripple from the so-called 12v wall wart.
I could have built or bought a clean low power 12v PS but I just
hooked the OCXO to my 50A Astron PS. No spurs, now.
To set up the OCXO use a good frequency counter or net the oscillator
to WWV 10-MHz (if you can hear it). I have a Rubidium source that I
use as my standard and measure with a microwave frequency
counter. But that is not needed for basic use on HF/6m with the
K3EXREF. Note that OCXO will drift off frequency about 1-Hz in six
months so regular checking a couple times per year is needed. GPSDO
does not need this.
73, Ed - KL7UW
Date: Wed, 09 Mar 2016 12:37:04 -0500
From: "Gary Smith" <[email protected]>
To: [email protected]
Subject: [Elecraft] 10 MHz external reference
Message-ID: <[email protected]>
Content-Type: text/plain; charset=US-ASCII
I ordered the K3EXREF and thought it was the oscillator itself which
would provide the external signal source to the K3s. I thought this
was all I was going to need but I see now that is not the case.
Looking on the Elecraft order page, they don't sell a reference
source.
What external 10-MHz reference signal source might I find get that is
not terribly expensive that will do the proper job and allow me to
get this working?
Thanks & 73,
Gary
KA1J
73, Ed - KL7UW
http://www.kl7uw.com
"Kits made by KL7UW"
Dubus Mag business:
[email protected]
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