[Elecraft] 10 MHz external reference - GPSDO

[Edward R Cole]

Olli,

Referring to page 8 in the K3 Owner's Manual (may be a different page 
for the K3s):

"Frequency Stability  +/- 5 ppm for the TCXO standard; +/- 1ppm for 
the optional TCXO."
TCXO-1 and TCXO-3 respectively mentioned above.

ppm means one part per million (1Hz per million Hz which is 1Hz per MHz).
So frequency drift is proportional to the operating frequency.

1ppm at 10-MHz is 10-Hz;1ppm at 28-MHz is 28-Hz
TCXO-1 provides 5ppm (+/- 50 Hz at 10-MHz and +/- 140 Hz at 28-MHz)
TCXO-3 provides 1ppm (+/- 10 Hz at 10-MHz and +/- 28 Hz at 28-MHz)

the basic frequency stability is determined by which TCXO is 
installed in your K3.

EXREF "essentially" checks frequency drift of whichever TCXO you have 
installed at a fixed time interval of about 4-seconds.  It uses a 
high stability 10-MHz external signal to compare with the 49.380-MHz 
TCXO and corrects the drift that occurs over the 4-second interval.

My measurements of the TCXO-3 show about half the published spec of 
1ppm (14 Hz at 28-MHz) and the EXREF limits the drift of the TCXO-3 
to about 2 Hz.  If I had the TCXO-1 installed, I would expect five 
times as much drift.

So which TCXO you install directly impacts frequency stability.  The 
EXREF reduces that by about an order of five.  The EXREF is not the 
source of stable LO but merely improves what you have 
installed.  Does that clear it up?

73, Ed - KL7UW

The question to ask is what amount of frequency stability and 
accuracy is important for your type of operations.

Date: Sat, 12 Mar 2016 08:17:32 +0100
From: Oliver Dr?se <droese at necg.de>
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] 10 MHz external reference - GPSDO
Message-ID: <56E3C28C.90803 at necg.de>
Content-Type: text/plain; charset=windows-1252; format=flowed

Why would I need the TCXO-3 instead of the TCXO-1 when using the K3EXREF
if the accuracy and stability is provided by the EXREF? Am I overlooking
something here?

Tnx & 73, Olli - DH8BQA

Contest, DX & radio projects: http://www.dh8bqa.de



73, Ed - KL7UW
http://www.kl7uw.com
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