[Elecraft] Suggestions for 10 MHz Signal Source for the K3?

[Dave, G4AON]

Like I guess quite a few others, I have been down the high stability 
reference route and currently have the following 10 MHz sources:

60 KHz (MSF and possibly WWV) locked plain crystal oscillator, it's 
based on the G4JNT MK2 from RadCom (http://www.g4jnt.com/freqlock.htm). 
It works well enough and is easy and cheap to build/align. The 
limitation is the short term stability which is perhaps academic when 
used to lock a HF transceiver and is around 1 part in 10^8 (same 
stability as the older UK Quartzlock 198 KHz units), also I am not sure 
how immune it would be in the presence of high levels of HF RF. Locks 
and stable within 5 minutes or so from switch on, low current consumption.

Surplus rubidium... These appear from time to time, I was given one by a 
local surplus dealer who seemed to have more than there was a market for 
a few years ago. They are used in cellular and similar sites and are 
probably good for quite a few hours of service, however they have a 
finite life and appear on the surplus market when removed for upgrade or 
on routine service, so don't pay much for one. Current drain is quite 
high, typically needing 2 Amps at 24 Volts initially then dropping after 
warm up. Stable around 15 ~ 20 minutes from switch on. Needs additional 
power supply and cabinet/heatsink.

GPS controlled crystal oven... Mine appeared on eBay as a part home 
built unit, there are a variety of these that pop up at times. Mine uses 
a Toyo high stability OCXO and is superbly stable and will site in 
perfect sync with the rubidium for days. Locked and stable around 15 ~ 
30 minutes from switch on, needs well sited external antenna (not one 
sitting in the shack window). Current consumption around half that of a 
rubidium when fitted with an OCXO. The best option of all for a long 
term accurate reference.

If you want an OCXO there are currently several "double ovens" listed on 
eBay.com for $45 including worldwide shipping from China. They need a 
GPS or MSF/WWV locked oscillator to set accurately on frequency, warm up 
time 15 ~ 30 minutes. High stability oscillators/sources can be compared 
for phase/frequency with a dual beam oscilloscope, listening for a beat 
note between them is not sufficient at this level of accuracy.

I don't plan to fit a K3EXREF, it seems like a nice idea but my K3 was 
only 2 Hz off frequency at 50 MHz a few days ago and it hasn't been 
adjusted for several months. My K3 has the KTCXO3-1 fitted and dates 
from 2007, so the TCXO is fairly well aged by now.

73 Dave, G4AON
-----------------------
/I am considering a K3EXREF just for fun, no other
reason.

Looking for suggestions for a reasonably priced 10
MHz external signal source.

Can anyone offer some suggestions? GPSDO? OCXO?
Rubidium Standard?
<SNIP>
73 de N1LQ-Dave/