[time-nuts] Introduction and info about a Lucent RFTG

GandalfG8 at aol.com GandalfG8 at aol.com
Sat Jul 5 08:06:03 EDT 2014

Hi Denver
When you refer to one "side" or the other, do you have the complete RFTG  
unit with the two modules?
I only have the internals of the Rubidium module so would hardly claim to  
be an expert on these, or on much else for that matter:-), but as I 
understand  it from the documentation this is a "reduntant" system, in that either 
the GPSDO  or the Rubidium module is active at any one time with the other in 
In other words, there's no suggestion that the Rubidium module is locked to 
 GPS, it is indeed free running, whilst the GPS module is used to 
discipline  its own crystal oscillator.
However, although the "free running" Rubidium module will need occasional  
adjustment, as opposed to the GPSDO wich shoudn't, a free running Rubidium  
reference is still not something to be sneezed at.
Section 2.1 "RFTG Functionality", in the documentation refers to this in  
more detail.
There was a fair bit of discussion here at one time regarding these so I'm  
surprised you haven't found more in the archives. For example, another list 
 member, Skip Withrow, produced an article in January 2013 detailing how to 
 modify the RFTGm GPSDO to obtain a 10MHz output, which he suggests should 
also  apply to the earlier versions and I've also seen information on the 
Rubidium  modules.
Because my Rubidium module arrived with just the two  attached PCBs and no 
outer metalwork whatsoever it was easier for me anyway  to just put the 
15MHz generator board to one side and use the interface board  only with its 
special D connector still attached to make the thing  functional.
If I'd had the complete unit, including metalwork, I would probably have  
approached it differently.
On my unit at least the actual Rubidium module was an Efratom FRS  and 
there's documentation available online for these should you wish to run  it 
stand alone
However, it would seem to me that without too much work, and utilising  the 
existing metalwork, these two units between them could provide the basis 
for  a 10MHz Rubidium Standard plus a separate 10MHz GPSDO,  but turning them  
into a GPS disciplined Rubidium unit perhaps not quite so  
In a message dated 05/07/2014 07:38:44 GMT Daylight Time, dencohe at gmail.com 

Thank  Rex and Paul for the replies

>From what I understand my RFTG has a GPSDO  on oneside that has a crystal
oven inside it, and a rubidium source on the  other side. The rubidium
source takes a signal from the GPSDO side and uses  that for longer term
stability. But If I am understanding you, Rex, that  the rubidium is really
not a gps locked oscillator and just a free running  device. I will start
tearing down the unit to figure out if I can make  something more usable out
of it. I will make sure to document it and post  it somewhere on the web. I
read somewhere on this group that there is a way  to bypass the 15MHz
generating circuit and use the existing hardware  amplifier and distribution
at 10MHz. I will also be looking into that as  well. Rex, you are correct as
there is no power supply inside and I have it  hooked up to a open frame
type switching supply externally.

Paul - I  will be setting up my GPS antenna shortly and trying to get it to
lock to  GPS for a more precise reference.

Thanks all

On  Fri, Jul 4, 2014 at 9:38 PM, Rex <rexa at sonic.net> wrote:

>  Several years ago there were a number of these showing up pretty cheap  
> eBay, so I bought one. As I recall there were a couple of similar  
> with some differences so take this recollection with a grain  of salt.
> I did some tracing of the internals on the one I had  and found the
> rubidium unit had no connection on the tuning pin  (C-field) to the board
> circuits. So it was free running, only for  backup in the system, and not
> GPS lockable. I don't remember there  being any useful power supply in the
> box, so my advice would be to  remove the LPRO rubidium and use it 
> (It does need heat  sinking, so maybe some parts of the box mechanicals 
> useful.) In my  opinion, working out how to use the supporting circuit 
> is not  worth the effort, unless you really have a need for the 15 MHz 
>  create.
> You should be able to find documentation for the  internal module LPRO
> rubidiums on the web. I haven't looked today but  KO4BB site probably has 
> On 7/4/2014 1:47  PM, Denver wrote:
>> Hi all,
>> My name  is Denver I am currently a freshman in college and the time bug
>>  has
>> struck me. I recently acquired a Lucent RFTG on ebay to have a  time
>> standard for my lab(and yes already realize its 15MHz output  but may be
>> able to change that and or just use the 10MHz test  point from the 
>> source). I made a power connector for it.  Now that I have power applied
>> and
>> sort of verified its  operation I am looking for more info about the
>> connectors on the  front panel. I have the KO4BB user documentation on it
>> but it  doesn't mention much about connectors and pinouts. I also have
>>  already searched the group for other mentions of the RFTG but all I  am
>> able
>> to come up with is some of the newer models  the -m and such. Maybe one 
>> you could help point me in the right  direction or give me some other 
>> on how to get more use out  of this unit.
>> Thanks in advance
>>  -Denver
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