Bill Hawkins said the following on 12/31/2006 02:15 AM:

I suspect it would be pretty easy to tap off the 10MHz signal from the
XO in addition to (or instead of) the 15MHz output.

John

One approach would be to divide the 15 MHz by three and then mix the
resultant 5 MHz with the original 15 MHz to get 10 MHz: original minus one
third equals two thirds.

John  WA4WDL

----- Original Message -----
From: "John Ackermann N8UR" jra@febo.com
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Sunday, December 31, 2006 9:01 AM
Subject: Re: [time-nuts] New pics of RFTG-m-Rb, and some comparison details

If the unit has an internal 10 MHz OCXO, it is hard to imagine the 15
MHz being cleaner than the 10 MHz, so it would seem the best way
(simpler and cleaner) is actually to tap off the OCXO with a suitable
buffer amp.

Didier KO4BB

jmfranke wrote:

Pretty sure that the RB is disciplined from the XO through the interface
cable. I posted the pinout a couple times before so people can make their
own.

As for the 10 MHz on the Rb .... Why not just get a mini-circuits splitter
(cheap on eBay) so you have the 10 MHz from the RB and can still run it to
the XO?

Jason

On Sun, Dec 31, 2006 at 09:22:50AM -0600, Jason Rabel wrote:

While I may have too much shoe leather in mouth to think

clearly, it seems that the following reasoning certainly leads to a
disciplined Rb...

Presumably the design is intended to supply timing and frequency

reference to a cell site just as reliably as possible in the event of
various kinds of failures.

Clearly the most common failure is loss of GPS (birds,

lightning, moisture in the antenna assembly, damage to or water in
cables, rodents, local interference, problems with the GPS constellation
etc.)

And clearly even quite a good OCXO isn't going to meet the

holdover spec for more than a very few hours (1 microsecond drift in 1
day is 1.157 parts in 10^11).  If you can't fix it after that you're
screwed and the site goes down.

So the logical thing to do is use a rubidium reference which can

very easily have less than one part in 10^11 drift per day and typically
much better than that.  This gives much more time to repair, and if the
Rb is doing well that may extend into several days or even a week or
more.  Enough time to get to the site and fix the antenna, cables,
etc...

But obviously the only way the Rb is useful is if it is

disciplined somehow so it starts out dead on.  Relying on the factory C
field setting to be within parts in 10^11 years later is ridiculous
considering variations in local magnetic field, aging etc... it is
probably not possible to do much better than parts in 10^9 in a factory
shipped without field adjustment situation in fact.

And it is quite clear that the dual module design is

deliberately engineered for a reason - each module can independently
produce the 1 PPS and 15 MHz needed and they are independent boxes that
can be hot swapped without taking down the cell site.  So if the GPS
(XO) box dies the site can and will continue with 1 PPS from the Rb and
Lits 15 MHz while a new XO box is hot swapped in (and presumably the XO
fails more often due to GPS receiver failures from lightning hits).

Further, if the more complex and less reliable Rb dies a new

(RB) module can be swapped in without killing the site either.  All
that is lost is holdover performance.

And at least possibly the phase noise of the OCXO beats the LPRO

so optimum site performance is with the OCXO rather than a Rb reference.
Thus the normal mode may be to use the 15 MHz from the OCXO with the 15
MHz from the Rb as backup.

The big question is why disciplining the OCXO requires a 16 bit

A/D and disciplining the Rb does not...  of course disciplining the Rb
quite possibly only works with both modules present - it is not
completely clear that the stand alone m-RB module will lock to a random
1 PPS since there is no obvious need for this in the overall system
architecture.  It is interesting that 10 MHz from the Rb is an input to
the XO - whether this is to supply redundancy in the 15 MHz/1 PPS or
just to allow the XO to work from another master source of 10 MHz isn't
clear (or perhaps the 10 MHz input to the XO from the Rb is required to
get the Rb to discipline).

--
Dave Emery N1PRE,  die@dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in
celebration of what could have been, but wasn't and is not to be now either."

On Sun, 31 Dec 2006 09:22:50 -0600, "Jason Rabel"
jason@extremeoverclocking.com wrote:

I don't so. I think the RB units have just their factory calibration.
Read Richard H McCorkle's message in the other thread. He describes the
over-all system and it seems to match what is known about stuff that's
in the boxes, so far.

I just got an RFG-RB which seems to be a few years newer than the
RFTG-m-RB's. In that one, I can't find any connection to the LPRO Rb
module, in it, that could cause it to be disciplined. The one I have
seems to be stipped down from the RFTG-m-RB. The main board is much
simpler but seems to have the same basic circuitry for 15 MHz
generation.

So, if we have two sources of 15 MHz in a CDMA minicell, each with
its own SMA connector, what module receives those two sources and
decides which one to use?

Why use XO and Rb when either could be made redundant for extended
reliability? (not the British sense of "made redundant")

Bill Hawkins

-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Rex
Sent: Sunday, December 31, 2006 7:08 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] New pics of RFTG-m-Rb, and some comparison
details

On Sun, 31 Dec 2006 09:22:50 -0600, "Jason Rabel"
jason@extremeoverclocking.com wrote:

I don't so. I think the RB units have just their factory calibration.
Read Richard H McCorkle's message in the other thread. He describes the
over-all system and it seems to match what is known about stuff that's
in the boxes, so far.

I just got an RFG-RB which seems to be a few years newer than the
RFTG-m-RB's. In that one, I can't find any connection to the LPRO Rb
module, in it, that could cause it to be disciplined. The one I have
seems to be stipped down from the RFTG-m-RB. The main board is much
simpler but seems to have the same basic circuitry for 15 MHz
generation.

time-nuts mailing list
time-nuts@febo.com
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts

The two units go in (what was told to me) an open frame chassis, it has SMA
and I believe DB-15 connections along the top. The connections on the
chassis split the signals even more, presumably for routing to the rest of
the cell.

http://campus.pari.edu/k4cso/gps/Lucent/

I was able to contact the guy that owns that unit, but his XO was hit by
lighting a while back and it's currently out of action, so he wasn't able to
give me info on any signaling, just the cable pinouts.

I would assume you could use the XO by itself, since it has the GPS. Then
optionally connect the Rb for longer holdover. From what I was told, on
initial power up the XO is the primary until the Rb warms up, then it
switches to the primary and the XO LED changes to standby.

Jason

P.S. Happy New Year Everyone!

The RFG-XO doesn't have a GPS unit in it. It has a 10 MHz in, and of course
the 15 MHz out. It also only has three DB9 connection, the 24V, interface,
and alarm.... It is missing the RS-485/1PPS connection.

Similar the RFG-RB doesn't have the RS-485/1PPS connection.

David,

Your thinking pretty much along the same lines as me from your post.

FYI, I didn't mean the XO itself, I meant the "XO module" (specifically the
GPS/PPS signal).

There is also a "RFTG-u REF 0" on eBay, however the picture is so poor I
can't make out all the connections. But it too has the alarm, 24V,
Interface, RS-485/1PPS, and a pair of SMA connections. It has one additional
DB9 connection (that I can't read, I think it might be another Interface).
The function of the unit itself is unimportant, but this just illustrates
the system is modular and probably signaling between modules is very basic
since they are all the same size / connections.

I agree with you that the RB has to be disciplined / adjusted somehow, and
not by opening the chassis. Just from the design of the shell it is obvious
that it is not meant to be opened regularly, definitely not in the field,
and there is no easy access to the RB adjustment screw (especially if the
unit was in the open-frame chassis and powered on).

BTW, did anyone else's RFTG smell like a stinky old sock, or a gym locker
room? Pee-yew!

Happy New Year everyone, this is going to be my last post for the year. :)

Jason