[Elecraft] 10 MHz Reference Oscillator

[Edward R Cole]

Back in the 1950's all radios drifted a lot at cold start...that is 
why many let their receivers run continuously.

OCXO = Oven Controlled Xtal Oscillator.  I utilizes an insulated 
enclosure heated above the ambient temperature to provide a very 
stable operating temperature for the xtal oscillator.  Thus they need 
to be at stable operating temp to provide very stable "short-term" 
10-MHz reference signal.  30-40 minutes from cold start is about 
right.  I just run mine 24/7.  Originally I used a RS 1.5A wall cube 
charging a large gell-cell battery for 12v power but after 
discovering bad 120-Hz ripple on the voltage am just using a good 12v 
PS made by Astron.  Short term frequency stability is +/-5 E-12 or in 
non-scientific nomenclature +/- 0.000005 Hz.  The long-term stability 
is +/-5 E-5 which is about +/- 5Hz so one must periodically adjust 
(or recalibrate) the OCXO with an accurate frequency.  I find mine 
drifts about 1-Hz over 6-month.

The K3EXREF keeps the K3 with TCXO-3 to about 2 to 3 Hz at 28-MHz 
using a OCXO as reference.  Plenty good enough for just about anyone.

I also use a surplus "Russian" Morion OCXO bought for $45 from 
e-bay.  Recently they are available for much less with double-oven 
design or sine wave versions.  I bought a couple sine-wave OCXO for 
$25 in the last year.

They do require a 5v regulator and multi-turn 100K pot plus a couple 
capacitors and fixed resistors for the frequency control lead of the 
OCXO (about $30 of parts).  I mount my OCXO on a small RS project pc 
board.  Yes it requires some assembly with soldering iron (but no sm 
stuff).  I have a Rubidium reference for calibrating my OCXO...It 
also requires a long warm up.

So if you travel with your K3 a lot then probably a GPSDO is a better 
choice though one also requires them to have a good lock on GPS which 
can take a minute or so for some.

73, Ed - KL7uW
I was a beta-tester on the K3EXREF


----------------
From: brian <alsopb at nc.rr.com>
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] 10 MHz Reference Oscillator
Message-ID: <5634D307.7070102 at nc.rr.com>
Content-Type: text/plain; charset=windows-1252; format=flowed

Ron,

The MV89A is pretty incredible-- especially for the price.

I think two statements in your posting contradict each other though.
It isn't basically "on frequency" from a cold start.   It drifts 10's of
Hz until the oven temp and oscillator stabilizes.
The second statement about taking 40 minutes is more accurate.

Upon receipt of mine, there was some calibration needed to have it
accurate < 1 Hz.

After calibration and warmups of 2 hours to days, the residual drift was
incredibly low <0.003 Hz/day!

For those who can live with it being powered continuously, it is an
excellent unit to discipline the K3.

73 DE Brian/K3KO




73, Ed - KL7UW
http://www.kl7uw.com
     "Kits made by KL7UW"
Dubus Mag business:
     dubususa at gmail.com