[time-nuts] Racal Dana 9478 frequency distribution system with option 04B high stability oven (5x10^-10/day aging rate).

[Dr. David Kirkby]

I want a distribution amplifier to distribute 10 MHz from an HP GPS
receiver to various bits of test kit - spectrum analyzer, VNA, signal
generators, HP 5370B time interval counters, signal generators etc.
Currently I am using 75 ohm video amplifiers, but I suspect that is sub
optimal. I also don't like the form factor of this amplifier - I would
prefer a 19" rack mount unit.

Does anyone know how well the Racial 9478 performs? If my understanding is
correct this is not simply an amplifier, but has its own internal high
stability reference oscillator, which then feeds 9 independent outputs, all
of which have their own amplifier. The internal OCXO will phase lock that
to an external reference.

Fundamentally, it does not seem a great idea to me to lock one OCXO to GPS
then lock a second OCXO to the first OCXO. But maybe I am mistaken.

I have the chance to buy one for £150 (GBP) but are a bit worried the
performance.

Any comments?

Dave.
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[David C. Partridge]

FWIW it is trivial to modify these video distribution amps for 50 ohm output - you just need to change the output resistors form 75 ohm to 50 ohm on the board after the op-amp.

David

-----Original Message-----
From: time-nuts [mailto:time-nuts-***@lists.febo.com] On Behalf Of Dr. David Kirkby
Sent: 04 November 2018 10:44
To: time-***@lists.febo.com
Subject: [time-nuts] Racal Dana 9478 frequency distribution system with option 04B high stability oven (5x10^-10/day aging rate).

I want a distribution amplifier to distribute 10 MHz from an HP GPS
:
Currently I am using 75 ohm video amplifiers, but I suspect that is sub
optimal.


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[Scott McGrath]

Racal overall has a reputation for making very high quality instruments, Since the OCXO is an option, and the price is right on the DA, I’d probably buy it.

Also thinking since its an option the OCXO can probably be switched out of circuit or removed entirely.

Im guessing Racal thought that adding an OCXO would be a feature for shops that did not have a frequency standard and/or one that used a different frequency than ‘standard’ like a TV station. So everything would be phase locked to a master clock irrespective of frequency.



Content by Scott
Typos by Siri

On Nov 4, 2018, at 6:50 AM, David C. Partridge <***@perdrix.co.uk> wrote:

FWIW it is trivial to modify these video distribution amps for 50 ohm output - you just need to change the output resistors form 75 ohm to 50 ohm on the board after the op-amp.

David

-----Original Message-----
From: time-nuts [mailto:time-nuts-***@lists.febo.com] On Behalf Of Dr. David Kirkby
Sent: 04 November 2018 10:44
To: time-***@lists.febo.com
Subject: [time-nuts] Racal Dana 9478 frequency distribution system with option 04B high stability oven (5x10^-10/day aging rate).

I want a distribution amplifier to distribute 10 MHz from an HP GPS
:
Currently I am using 75 ohm video amplifiers, but I suspect that is sub
optimal.


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[Dr. David Kirkby]

Post by David C. Partridge
FWIW it is trivial to modify these video distribution amps for 50 ohm
output - you just need to change the output resistors form 75 ohm to 50 ohm
on the board after the op-amp.
David

Three was a discussion about the particular video amplifier here some years
back, as they were on eBay and someone on this list made us aware of it.

Part of the discussion was converting to 50 ohms, but someone pointed out
it was pushing the limits of the op-amp.

But I don't like the form factor of the unit either.

I have for some time looking for another distribution amplifier, but I was
offered this at £150 including delivery. I think I will take it.

Dave.
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[Heinz Breuer]

It seems to be a very good price.
There is a Racal Dana 9480 fully equipped with 40 outputs listed on eBay Germany for EUR 795.
Nice to have but I don't need 40 outputs.
vy 73 Heinz DH2FA, KM5VT

Von meinem iPhone gesendet

Post by Dr. David Kirkby

Post by David C. Partridge
FWIW it is trivial to modify these video distribution amps for 50 ohm
output - you just need to change the output resistors form 75 ohm to 50 ohm
on the board after the op-amp.
David

Three was a discussion about the particular video amplifier here some years
back, as they were on eBay and someone on this list made us aware of it.
Part of the discussion was converting to 50 ohms, but someone pointed out
it was pushing the limits of the op-amp.
But I don't like the form factor of the unit either.
I have for some time looking for another distribution amplifier, but I was
offered this at £150 including delivery. I think I will take it.
Dave.
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[Bob kb8tq]

Hi

One would *guess* that the PLL bandwidth in the 9578 is wider than what you see in a typical
GPSDO. As long as they don’t both line up at the same point, noise and phase peaking should
not be a big deal. Depending on how clean your GPSDO is, the 9578 might clean things up a bit.

For timing / high precision, putting another PLL into things is going to add some delay and possibly
some temperature dependence. Since you are running normal test gear, neither of those issues
should be significant enough to impact anything. In this environment 75 ohms vs 50 ohms is also
not a big deal, but it will have slightly more impact, fix it if you can, don’t sweat it if you can’t.

Bob

Post by Dr. David Kirkby
I want a distribution amplifier to distribute 10 MHz from an HP GPS
receiver to various bits of test kit - spectrum analyzer, VNA, signal
generators, HP 5370B time interval counters, signal generators etc.
Currently I am using 75 ohm video amplifiers, but I suspect that is sub
optimal. I also don't like the form factor of this amplifier - I would
prefer a 19" rack mount unit.
Does anyone know how well the Racial 9478 performs? If my understanding is
correct this is not simply an amplifier, but has its own internal high
stability reference oscillator, which then feeds 9 independent outputs, all
of which have their own amplifier. The internal OCXO will phase lock that
to an external reference.
Fundamentally, it does not seem a great idea to me to lock one OCXO to GPS
then lock a second OCXO to the first OCXO. But maybe I am mistaken.
I have the chance to buy one for £150 (GBP) but are a bit worried the
performance.
Any comments?
Dave.
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[George Atkinson via time-nuts]

The 9478 is an excellent unit but slightly unconventional. It does not discipline the internal OXCO to the external standard when present. It has a 10MHz PLL VFO tat is locked to either the internal OCXO or external refernce depeding what is available. If the external reference is present te VFO is locked to that and the internal OCXO is on but not used. If the external refernce is missing the internal OXCO is used. Effectively when used with an external reference the internal OXCO is a backup.
The service manual is out on the web nd it would nt be difficult to re-configure a 9478 as a dumb 10MHz Distribution unit but this would b a waste. 19" video distribution amplifiers are out there too.
I do have a spare NOS Austron modular 3U 19" rack with distribution modules in it but I'd have to check exactly what it has and I'm in the USA at the moment. If you are interested I can look when I get bck next week.
Robert G8RPI

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[Bob Bownes]

Video distribution amplifiers are a very good and inexpensive solution to
this problem. Think I paid $5US for my 24 port one (which is actually 3x
dual 1 in 4 out units). I converted one of them from 75 ohm to 50Ω and
didn't bother doing the rest as it made no discernible difference for
timing purposes.

On Thu, Nov 8, 2018 at 10:23 AM George Atkinson via time-nuts <

Post by George Atkinson via time-nuts
The 9478 is an excellent unit but slightly unconventional. It does not
discipline the internal OXCO to the external standard when present. It has
a 10MHz PLL VFO tat is locked to either the internal OCXO or external
refernce depeding what is available. If the external reference is present
te VFO is locked to that and the internal OCXO is on but not used. If the
external refernce is missing the internal OXCO is used. Effectively when
used with an external reference the internal OXCO is a backup.
The service manual is out on the web nd it would nt be difficult to
re-configure a 9478 as a dumb 10MHz Distribution unit but this would b a
waste. 19" video distribution amplifiers are out there too.
I do have a spare NOS Austron modular 3U 19" rack with distribution
modules in it but I'd have to check exactly what it has and I'm in the USA
at the moment. If you are interested I can look when I get bck next week.
Robert G8RPI
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