[Elecraft] Tr: K3 Ref connector

Sat May 16 21:46:50 EDT 2009

I have bought items from fluke.l on eBay who sells them. He sells the 
GPS-DO, the Efratom device, adn the one I bought which is an FE-5860A 
Rubidium frequency standard from him and hooked it up last night. I've 
found fluke.l to be responsive and honest, and he ships quickly. (If you 
are in a hurry, ask about shipping options.)

Here is a report on what I've learned and done so far, and where to find 
more info, plus a few rants on what I'd like to do myself.

If nothing else, I've been annoying my family and co-workers by saying 
things like, "Let me get back to you on that after I finish the 
modifications I'm making to my Rubidium atomic clock." So, if you really 
want to know about these, don't listen to me, but instead look at these 
resources:
1. There's a mailing list called time-nuts where people who actually 
understand them hang out, and
2. Connie http://www.k5cm.com/ runs a monthly frequency measuring test 
and they have a mailing list there as well. (I placed fairly high in the 
last ARRL FMT, though not at the top.)
3. If you order an FE-5680A, this page is very useful: 
http://www.dd1us.de/Downloads/precise%20reference%20frequency%20rev%200_4.pdf

Here's what I've learned from the manuals and reference materials:
A Rubidium reference oscillator uses a Rubidium bulb, which is heated 
and the resulting gas tested for light absorption in the presence of an 
external RF field in the 6 GHz range. The microwave signal is tuned in a 
feedback loop to look for the peak in absorption (a very small change on 
the order of 0.1%) and that locks the oscillator in the known frequency 
of 6 834 682 610.904 324 Hz. Another external field is used to change 
this slightly, but I'm not the person to explain the physics. A 136x 
divider brings this down to 50.566+ Mhz, so you wind up with what is 
essentially a very stable oscillator with low phase noise. This 50+Mhz 
signal is then used as the reference frequency for our old friend the 
AD9830A DDS chip, which can then be programmed via an internal 
microprocessor and RS232 to whatever frequency you want, within the 
Nyquist range and the output filter range. By default these come set for 
~8Mhz (2^23 Hz, which is divided down to get a 1Hz output).

In most of the surplus units, this signal isn't available externally, 
but only internally with a connector that looks like a Hirose U.Fl 
connector. (If anybody knows different, please let me know, as I already 
have a U.Fl to BNC bulkhead pigtail on order.)

I used the default 8,388,608 Hz signal out to a test pin to calibrate my 
FCC-1 kit, which it turned out was already within 1Hz.
I also tried using it to calibrate my K3 REF CAL, but I'd turned the K3 
off earlier and it wasn't warmed up.

What I'd like to do: once my connector pigtail arrives, I'll put it in 
the FE-5860A and make a stab a quick python program to read the 
frequency with fldigi's in Freq Cal mode and read the data from fldigi's 
remote XML interface and use the K3 RS232 to control the REF CAL 
setting. Of course, this hack would just automate a manual process, and 
doesn't provide a way to keep the K3 on frequency during TX.

Leigh/WA5ZNU

> Hi
>
> Talking about rubidium standards. 
>
> Does anyone have any experience with buying and using the EFRATOM LPRO-101 rubidium standard that  seems to be readily available from  the many Chinese sellers on Ebay?
>
> I am tossing up between the LPRO rubidium  and the Thunderbolt GPS standard. The Thunderbolt  makes a lot of sense since it  does  not depend on a tube that can wear out or go out of lock.
>
> Will Elecraft be producing both the frequency standard and the interface or just the interface?
>
> 73
> Craig
>
>
>       
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