[time-nuts] Rubidium Performance: DDS noise effect on 10 MHz

[EWKehren at aol.com]

Maybe his are new. But I bought one from ggg*fitting that was listed as new 
 turned out very used, and in conversation with them they had to admit they 
do  not know what they have. If it still has its original factory setting, 
measuring  the frequency will tell you if it had extensive running time or 
not.
Bert Kehren
 
 
In a message dated 2/4/2012 4:44:20 A.M. Eastern Standard Time,  
jmiles at pop.net writes:

>  From your comments, it sounds like you may be measuring  one of the
> earlier 5680A's that could be tuned over a large range with  a DDS output.
> 
> These earlier ones had a 50.25 MHz internal osc  which was locked after
> multiplication to the rubidium frequency. Then  there was a DDS on the
> output that could be programmed over a wide  frequency range.

That sounds plausible.   I haven't taken the  time to bring myself 100% up 
to
speed with the many different variations  and options for these little 
boxes,
but I could swear I'm looking at a  low-resolution, unfiltered, uncleaned-up
DDS.

> The newer ones  have a 60 MHz internal oscillator. This is multiplied up
> to 6840 MHz  and subtractively mixed with ~5.3125 MHz from a DDS to get
> to the  rubidium frequency. The feedback from the rubidium cell locks the
> 60  Hz which is divided by 6 for the 10 MHz output. No DDS on the output
>  generation. The DDS in the loop can digitally adjust the rubidium lock
>  frequency that tunes the 60 MHz, to fine tune the output only around  10
> MHz.
> 
> Do you know which type of 5680A you are  measuring?

This one is marked S/N 0339-65969, purchased  from
http://www.ebay.com/itm/260930018124 .  It seems to have the  pinout
documented at http://vk2xv.djirra.com/tech_rubidium.htm for  serial
0127-96634 (pin 1=V+, pin 2=GND, pin 3=+5V, pin 7=RF  out.)   However, VK2XV
claims that s/n 96634 was  non-programmable.  I haven't tried hooking up a
serial terminal to  mine, but I did notice that there was some negative
voltage on one of the  other pins (9?) that might correspond to an RS-232
signal  level.

Can't complain too much at $40/each, anyway  I believe the  seller's claim
that these are new or nearly so, even though they look like  they've been
removed from an installation.  The internal foam  insulation is usually
discolored from heat, while it looks great in the two  units that I bought
from this seller.

--  john



_______________________________________________
time-nuts  mailing list -- time-nuts at febo.com
To unsubscribe, go to  
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the  instructions there.