Discussion:
Racal-Dana 1991 w. Option 4C - what is that ?
(too old to reply)
cfo
2012-01-20 14:45:55 UTC
Permalink
Hi Nuts

I just bought a Racal-Dana 1991 (german eb..) , with options
01 : Inputs in back
4C : Unknown ? , but maybe some OCXO (i hope)
55 : GPIB

Does anyone know what option 4C could be ?
I hope some super nice OCXO option from USAF , they have bases in .DE

CFO (Time nut beginner)
Dan Rae
2012-01-20 15:33:59 UTC
Permalink
Post by cfo
Hi Nuts
I just bought a Racal-Dana 1991 (german eb..) , with options
01 : Inputs in back
4C : Unknown ? , but maybe some OCXO (i hope)
55 : GPIB
Does anyone know what option 4C could be ?
I hope some super nice OCXO option from USAF , they have bases in .DE
Option 4C is not listed in the manual, but presumably it refers to the
timebase. You will be able to tell best by looking inside when it
arrives. Racal made a lot of different ovens of different qualities as
well as TCXOs. All the US military had were the 1300 MHz version 1992
counters with a very good OCXO inside, type 9462, so yours is a civilian
one, I'm afraid.

dr
cfo
2012-01-20 16:35:18 UTC
Permalink
Post by Dan Rae
Post by cfo
Hi Nuts
Inputs in back
4C : Unknown ? , but maybe some OCXO (i hope) 55 : GPIB
Does anyone know what option 4C could be ? I hope some super nice OCXO
option from USAF , they have bases in .DE
Option 4C is not listed in the manual, but presumably it refers to the
timebase. You will be able to tell best by looking inside when it
arrives. Racal made a lot of different ovens of different qualities as
well as TCXOs. All the US military had were the 1300 MHz version 1992
counters with a very good OCXO inside, type 9462, so yours is a civilian
one, I'm afraid.
dr
Daummm :-)

Well thats why i got an extra Tbolt for home , i just need some
distribution of the 10Mhz.

CFO
Larry McDavid
2012-01-20 17:18:32 UTC
Permalink
Racal Option 04C is not an ocxo. I received a Racal 1999 counter
advertised with "ovened" frequency standard but when I examined the
actual part installed, it was a simple modular oscillator, a NDK 23-9134
with only a single adjustment. It was not stable with room temperature
and devilish to adjust.

I complained to the Hong Kong seller and they sent me a Racal Option 04A
module as a replacement, which is oven controlled, but not the Racal
"High Stability Option 04E." This was a big improvement over the Option
04C (which is not described in any Racal literature I've found) but
still showed significant ambient temperature sensitivity and again had
only a single adjustment. I have subsequently replaced that with a Racal
9462 ocxo, the ocxo furnished as Option 04E and that has both COARSE and
FINE adjustments.

I now have a Racal 1992 counter/timer running with Option 04E, measuring
10 MHz from a HP Z3801A GPSDO. My current 15°F overnight room
temperature variation causes about 0.003 Hz change in displayed
frequency when counted with a 10-second gate period. The FINE frequency
adjustment is easy to adjust (with due care) and has no backlash or
short-term drift that I've seen. Others have reported "click-stops" and
short-term drift after adjustment but I've not seen that.

One does occasionally find Racal 9462 ocxo offered on eBay. Also, one
sometimes finds non-operational Racal instruments offered at low price
but which to have Option 04E installed. I convinced one seller to remove
the Option 04E module (the Racal 9462) and sell just that with much
lower shipping cost.

There is also what is evidently an older Racal frequency standard module
similar in appearance to the 9462 but which has screws attaching the end
plate rather than the soldered-can 9462; one of those is seen from time
to time on eBay from the UK but I have avoided that.

I believe the Option 04C was provided only to get the counter running
and that this option was offered as a low-cost solution to users who
planned to supply precision 10 MHz input to the rear panel frequency
standard connector.

The Racal 9462 ocxo is in a "hermetic" can with glass feed throughs,
with the can end cap soldered in place. I don't know what is inside the
9462 as I have not tried to open one. The can is not actually hermetic
because the interior is exposed when the adjustment cover screws are
removed to adjust the frequency. Those screws have a rubber o-ring in a
groove under the head of the screw so when the adjustment cover screws
are in place, the interior is well sealed. The ocxo itself actually
operates at 5 MHz and there is a small PWB on the end, soldered directly
to the feed through pins, that doubles the output frequency to 10 MHz.
I've acquired several 9462 ocxo of various age and there are both PTH
and SMT versions of the frequency doubler PWB.

The Racal Option 04E ocxo, the Racal 9462, seems to work very well for
its intended purpose.

Is the Racal 9462 ocxo, their Option 04E, actually in a double oven,
like the HP 10811? I don't know.

If interested, I have pictures of the exterior of these options.

There was a Racal Option 04R, a Rb standard, but I've never seen one.

All of these options interchange easily within the Racal 199n counters
and perhaps other Racal models as well. While there are Racal ocxo that
operate on 12 volts, all the ones I've seen operate on only 5 volts and
have a single cable to apply power and output 10 MHz. The are very easy
to replace.

Yes, like everyone else here, I'm working on a FEI FE-5680A. Who can
resist that?

Larry W6FUB
Post by cfo
Hi Nuts
I just bought a Racal-Dana 1991 (german eb..) , with options
01 : Inputs in back
4C : Unknown ? , but maybe some OCXO (i hope)
55 : GPIB
Does anyone know what option 4C could be ?
I hope some super nice OCXO option from USAF , they have bases in .DE
...
--
Best wishes,

Larry McDavid W6FUB
Anaheim, CA (20 miles southeast of Los Angeles, near Disneyland)
cfo
2012-01-30 17:24:50 UTC
Permalink
Post by Larry McDavid
One does occasionally find Racal 9462 ocxo offered on eBay. Also, one
sometimes finds non-operational Racal instruments offered at low price
but which to have Option 04E installed. I convinced one seller to remove
the Option 04E module (the Racal 9462) and sell just that with much
lower shipping cost.
There is also what is evidently an older Racal frequency standard module
similar in appearance to the 9462 but which has screws attaching the end
plate rather than the soldered-can 9462; one of those is seen from time
to time on eBay from the UK but I have avoided that.
I have been looking for a Racal 9462 ocxo , for my Racal-Dana 1991
counter. I will prob. use my Tbolt anyway , and save the money.

But i'm confused ... Is it a 5 Mhz or a 10 Mhz unit.

I have found pictures of one claiming it's 5Mhz
http://www.jbtech.de/parts/racal_dana/9462.html

But i have also received a picture from jaap , with a racal 9492 , where
it clearly says its a 10Mhz unit.

Can anyone clarify ?

I think there was an "option" that enabled the use of "other ocxo values"
is that why a 5Mhz can be used , in some 1991's ?

If i ever decide to get a OCXO , i would like to get the "right one".

Regards
CFO
Dan Rae
2012-01-30 17:49:36 UTC
Permalink
Post by cfo
I have been looking for a Racal 9462 ocxo , for my Racal-Dana 1991
counter. I will prob. use my Tbolt anyway , and save the money.
But i'm confused ... Is it a 5 Mhz or a 10 Mhz unit.
It is a 5MHz oven but has a doubler board fitted to it, when fitted to
the 1992.

I would suggest that if you have a t'bolt then you should use that as an
external reference.

Dan
John Howell
2012-01-30 18:08:17 UTC
Permalink
According to the manual (publication TH62B4 issue 4.10.91) options 04T, 04A, 04B are all 10MHz. No mention of 04c. I vaguely remember hearing that Racal were so satisfied with their 5MHz standards than rather than produce a 10MHz version they simply attached a frequency doubler. I have a 9421 with doubler board attached.

John H.
Post by cfo
Post by Larry McDavid
One does occasionally find Racal 9462 ocxo offered on eBay. Also, one
sometimes finds non-operational Racal instruments offered at low price
but which to have Option 04E installed. I convinced one seller to remove
the Option 04E module (the Racal 9462) and sell just that with much
lower shipping cost.
There is also what is evidently an older Racal frequency standard module
similar in appearance to the 9462 but which has screws attaching the end
plate rather than the soldered-can 9462; one of those is seen from time
to time on eBay from the UK but I have avoided that.
I have been looking for a Racal 9462 ocxo , for my Racal-Dana 1991
counter. I will prob. use my Tbolt anyway , and save the money.
But i'm confused ... Is it a 5 Mhz or a 10 Mhz unit.
I have found pictures of one claiming it's 5Mhz
http://www.jbtech.de/parts/racal_dana/9462.html
But i have also received a picture from jaap , with a racal 9492 , where
it clearly says its a 10Mhz unit.
Can anyone clarify ?
I think there was an "option" that enabled the use of "other ocxo values"
is that why a 5Mhz can be used , in some 1991's ?
If i ever decide to get a OCXO , i would like to get the "right one".
Regards
CFO
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Jean-Louis Oneto
2012-01-30 18:15:27 UTC
Permalink
I checked the documentations I have, the option 4C isn't mentionned, but
all the (Internal Reference) options 04x (04A=OCXO, 04B=High Stability
OCXO, 04T=TCXO, 04E=High Stability OCXO (?)) are 10 MHz. There is a
Reference Frequency Multiplier (Option 10) which allows to use 1, 2, 5
or 10 MHz as an external reference.
The parts numbers are:
option 04A: 11-1710 (oscillator), assy=9444
option 04B: 11-1711 (oscillator), assy=9423
option 04E: 404386
option 04T: 11-1610 (plate assy) + 19-1208 (oscillator PCB)
option 10: 19-1164
Hope that helps,
Regards,
Jean-Louis
Post by cfo
Post by Larry McDavid
One does occasionally find Racal 9462 ocxo offered on eBay. Also, one
sometimes finds non-operational Racal instruments offered at low price
but which to have Option 04E installed. I convinced one seller to remove
the Option 04E module (the Racal 9462) and sell just that with much
lower shipping cost.
There is also what is evidently an older Racal frequency standard module
similar in appearance to the 9462 but which has screws attaching the end
plate rather than the soldered-can 9462; one of those is seen from time
to time on eBay from the UK but I have avoided that.
I have been looking for a Racal 9462 ocxo , for my Racal-Dana 1991
counter. I will prob. use my Tbolt anyway , and save the money.
But i'm confused ... Is it a 5 Mhz or a 10 Mhz unit.
I have found pictures of one claiming it's 5Mhz
http://www.jbtech.de/parts/racal_dana/9462.html
But i have also received a picture from jaap , with a racal 9492 , where
it clearly says its a 10Mhz unit.
Can anyone clarify ?
I think there was an "option" that enabled the use of "other ocxo values"
is that why a 5Mhz can be used , in some 1991's ?
If i ever decide to get a OCXO , i would like to get the "right one".
Regards
CFO
_______________________________________________
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
--
Jean-Louis Oneto
OCA GeoAzur - Avenue Nicolas Copernic - 06130 Grasse - France
email: Jean-Louis.Oneto-***@public.gmane.org
phone: (+33)[0]4.93.40.53.80
cfo
2012-01-30 19:17:55 UTC
Permalink
Thank you everyone.

It makes sense now , that Racal might use a 5Mhz w. a freq-doubler.

I'll use my Tbolt as a ref , or the FEI-5680A i just got.
And keep an eye on E... , for a cheap Opt 4e :-)

CFO
Larry McDavid
2012-01-30 20:08:31 UTC
Permalink
The Racal 9462 ocxo uses a temperature-controlled 5 MHz crystal
oscillator inside a sealed can. On the outside end of the can is a small
circuit board that doubles the output frequency to 10 MHz. The ocxo
cable comes from this circuit board so the output to the counter is 10
MHz. The Racal 9462 operates on 5 vdc and the cable has only three
wires, two of which are provided by a shielded cable for the 10 MHz signal.

Depending on the age of the ocxo, this doubler circuit board can be
either PTH design or (on later units) SMT design.

My understanding is that a 5 MHz crystal is inherently more stable than
a 10 MHz crystal so better overall performance is achieved by using a 5
MHz crystal and doubling the output to get 10 MHz.

I have pictures of these OCXO if you are interested.

The Racal Option 04C is a really, really simple 10 MHz oscillator whose
performance is terrible! It is not described in any Racal publication I
have found and I think it was offered to customers who bought many
counters for use in applications where an external precision 10 MHz
source was to be used; the Option 04C allows the counter to operate
poorly until connected to an external precision 10 MHz source. Option
04E provides the Racal 9462 and there are other ocxo versions, such as
Option 04A, that offer better performance than 04C but not so good as
Option 04E.

Larry
Post by cfo
Post by Larry McDavid
One does occasionally find Racal 9462 ocxo offered on eBay. Also, one
sometimes finds non-operational Racal instruments offered at low price
but which to have Option 04E installed. I convinced one seller to remove
the Option 04E module (the Racal 9462) and sell just that with much
lower shipping cost.
There is also what is evidently an older Racal frequency standard module
similar in appearance to the 9462 but which has screws attaching the end
plate rather than the soldered-can 9462; one of those is seen from time
to time on eBay from the UK but I have avoided that.
I have been looking for a Racal 9462 ocxo , for my Racal-Dana 1991
counter. I will prob. use my Tbolt anyway , and save the money.
But i'm confused ... Is it a 5 Mhz or a 10 Mhz unit.
I have found pictures of one claiming it's 5Mhz
http://www.jbtech.de/parts/racal_dana/9462.html
But i have also received a picture from jaap , with a racal 9492 , where
it clearly says its a 10Mhz unit.
Can anyone clarify ?
I think there was an "option" that enabled the use of "other ocxo values"
is that why a 5Mhz can be used , in some 1991's ?
If i ever decide to get a OCXO , i would like to get the "right one".
Regards
CFO
_______________________________________________
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
--
Best wishes,

Larry McDavid W6FUB
Anaheim, CA (20 miles southeast of Los Angeles, near Disneyland)
David C. Partridge
2012-01-31 22:15:02 UTC
Permalink
It's a 5Mhz crystal with a frequency doubler at the output.

Dave
-----Original Message-----
From: time-nuts-bounces-***@public.gmane.org [mailto:time-nuts-bounces-***@public.gmane.org] On Behalf Of cfo
Sent: 30 January 2012 17:25
To: time-nuts-***@public.gmane.org
Subject: Re: [time-nuts] Racal-Dana 1991 w. Option 4C - what is that ?

On Fri, 20 Jan 2012 09:18:32 -0800, Larry McDavid wrote:



I have been looking for a Racal 9462 ocxo , for my Racal-Dana 1991 counter. I will prob. use my Tbolt anyway , and save the money.

But i'm confused ... Is it a 5 Mhz or a 10 Mhz unit.
Hal Murray
2012-01-30 22:01:06 UTC
Permalink
My understanding is that a 5 MHz crystal is inherently more stable than a
10 MHz crystal so better overall performance is achieved by using a 5 MHz
crystal and doubling the output to get 10 MHz.
What makes 5 MHz more stable than 10 MHz?

Why not 2.5 MHz and double twice? Or 1.25 MHz and three doublers?
--
These are my opinions, not necessarily my employer's. I hate spam.
Tom Van Baak
2012-01-31 05:41:27 UTC
Permalink
Post by Hal Murray
What makes 5 MHz more stable than 10 MHz?
Why not 2.5 MHz and double twice? Or 1.25 MHz and three doublers?
Apparently 2.5 MHz is the most stable of all for reasons not
fully understood, but accepted. That's why the early Sulzer
oscillators were 2.5 Mc. They doubled them to get 5 MHz.

I don't have a reference handy but there are charts and
curves in old papers on quartz technology that show a peak
in performance (Q?) around 2.5 MHz. Doubling, tripling, or
quadupling works too but you get noise at every stage so
this is not always a solution.

The 2.5 MHz blanks are very large and expensive; I heard
that's why the industry moved to 5 and then 10 MHz crystals.
Perhaps one of the xtal experts on the list can clarify this for us.

See also:

Brief History of the Development of Ultra-Precise Oscillators
http://www.ieee-uffc.org/main/history.asp?file=norton

Fifty Years of Progress in Quartz Crystal Frequency Standards
http://www.ieee-uffc.org/main/history.asp?file=frerking

/tvb
Alan Melia
2012-01-31 11:41:27 UTC
Permalink
Hi Tom I seem to remember seeing a 5MHz standard in a triple oven at PO
Research in London were I worked in 1961. The crystal was made there and was
a 5MHz 3rd overtone and either a plano-convex or double-convex shape, I
believe. They had a lens grinding machine for generating the blanks. This
was in the days of the use of natural quartz too.

Alan
G3NYK
----- Original Message -----
From: "Tom Van Baak" <tvb-AeR/***@public.gmane.org>
To: "Discussion of precise time and frequency measurement"
<time-nuts-***@public.gmane.org>
Sent: Tuesday, January 31, 2012 5:41 AM
Subject: Re: [time-nuts] Racal-Dana 1991 w. Option 4C - what is that ?
Post by Tom Van Baak
Post by Hal Murray
What makes 5 MHz more stable than 10 MHz?
Why not 2.5 MHz and double twice? Or 1.25 MHz and three doublers?
Apparently 2.5 MHz is the most stable of all for reasons not
fully understood, but accepted. That's why the early Sulzer
oscillators were 2.5 Mc. They doubled them to get 5 MHz.
I don't have a reference handy but there are charts and
curves in old papers on quartz technology that show a peak
in performance (Q?) around 2.5 MHz. Doubling, tripling, or
quadupling works too but you get noise at every stage so
this is not always a solution.
The 2.5 MHz blanks are very large and expensive; I heard
that's why the industry moved to 5 and then 10 MHz crystals.
Perhaps one of the xtal experts on the list can clarify this for us.
Brief History of the Development of Ultra-Precise Oscillators
http://www.ieee-uffc.org/main/history.asp?file=norton
Fifty Years of Progress in Quartz Crystal Frequency Standards
http://www.ieee-uffc.org/main/history.asp?file=frerking
/tvb
_______________________________________________
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Post by Tom Van Baak
and follow the instructions there.
Bob Camp
2012-02-01 00:28:44 UTC
Permalink
Hi

It's not all smoke and mirrors. The Q of quartz goes up as frequency goes down. Nobody really debates that. As frequency goes down blank diameter would need to grow to keep everything same / same. Again not much debate.

What does get a lot of debate is just how small you can get blank diameter and still get reasonable performance.

If people just liked 3" diameter crystal packages.....

Bob
Post by Tom Van Baak
Post by Hal Murray
What makes 5 MHz more stable than 10 MHz?
Why not 2.5 MHz and double twice? Or 1.25 MHz and three doublers?
Apparently 2.5 MHz is the most stable of all for reasons not
fully understood, but accepted. That's why the early Sulzer
oscillators were 2.5 Mc. They doubled them to get 5 MHz.
I don't have a reference handy but there are charts and
curves in old papers on quartz technology that show a peak
in performance (Q?) around 2.5 MHz. Doubling, tripling, or
quadupling works too but you get noise at every stage so
this is not always a solution.
The 2.5 MHz blanks are very large and expensive; I heard
that's why the industry moved to 5 and then 10 MHz crystals.
Perhaps one of the xtal experts on the list can clarify this for us.
Brief History of the Development of Ultra-Precise Oscillators
http://www.ieee-uffc.org/main/history.asp?file=norton
Fifty Years of Progress in Quartz Crystal Frequency Standards
http://www.ieee-uffc.org/main/history.asp?file=frerking
/tvb
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Clint Jay
2018-05-13 11:25:43 UTC
Permalink
I'm all for anything that encourages whisky growth
Flux can provide just the right kind of ionic leakage path that leads to
whisky growth
and eventual sudden shorts.
Dana
To make this very long story into a short one, I learned that the HP/
Symmetricom 58532A GPS Reference (timing) antennas use a simple patch
antenna instead of a quadrafilar antenna and that old solder flux
residue
will attenuate the even amplified GPS signal out of this antenna.
Flux seems unlikely to produce a sudden failure.
If flux was the problem, I'd expect it to work poorly when first
installed,
or maybe decay slowly over time as something changed.
--
These are my opinions. I hate spam.
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Larry McDavid
2018-05-13 20:53:24 UTC
Permalink
So there are 3D quadrifiliar GPS antennas; I am gratified to hear that
as I surely remember promotions for GPS antennas that showed a
quadrifiliar design.

Regarding GPS multipath, I agree that is a problem. But, here on the
flatlands of Anaheim, I can stand on the roof of my 2-storey home (where
the GPS antennas are located) and be the tallest thing around for many
miles. Yes, there are surrounding LA area mountains, but those are miles
and miles away. Trees? This is Southern California! There are no tall
trees anywhere near me. There is little nearby to produce GPS multipath.

GPS receivers, at least in my GPSDO units, have an Elevation Mask option
to inhibit processing data from satellites near the horizon. I believe I
set those to 10 or 15 degrees.

The Symmetricom 58532A antenna does use a patch element and does not
need the cone-shaped radome to provide space for a quadrifiliar element.
That cone shape must be entirely for environmental reasons for it surely
adds cost to the antenna. Snow release? Beats me! There is snow atop
Matterhorn Mountain in nearby Disneyland but non falls here...

Larry
Usually GPS antennas are patch antennas. The PROCOM GPS4 (I have 2 of
them) should be a real QFH (I haven't opened it to verify), the
Vaisala radiosonde RS92 has a real QFH. The Sarantel SL series seem is
a double helix not a classic QFH with the two different-size loops.
They name their series GeoHelix.
<https://www.datamatik.no/media/produkt/gps-4.pdf>
<https://www.wmo.int/pages/prog/www/IMOP/meetings/Upper-Air/Systems-Intercomp/Doc3-4(1)Vaisala.pdf>
<http://www.wless.ru/files/Accessaries/Antenna/sl1200%20product%20spec%20v7_1210.pdf>
...
--
Best wishes,

Larry McDavid W6FUB
Anaheim, California (SE of Los Angeles, near Disneyland)
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Bob kb8tq
2018-05-13 22:44:33 UTC
Permalink
Hi

The shape of the radome on your typical timing antenna is all because of birds. If the antenna is 60 feet up
a cell tower you do *not* want to have to pay a crew to go up there and knock the nest off of the antenna.

Even in the flatlands, you can get multipath. All it has to do is bounce off the ground and back to your antenna.
A wide open flat area actually is “ideal” for that particular type of problem ….

Bob
So there are 3D quadrifiliar GPS antennas; I am gratified to hear that as I surely remember promotions for GPS antennas that showed a quadrifiliar design.
Regarding GPS multipath, I agree that is a problem. But, here on the flatlands of Anaheim, I can stand on the roof of my 2-storey home (where the GPS antennas are located) and be the tallest thing around for many miles. Yes, there are surrounding LA area mountains, but those are miles and miles away. Trees? This is Southern California! There are no tall trees anywhere near me. There is little nearby to produce GPS multipath.
GPS receivers, at least in my GPSDO units, have an Elevation Mask option to inhibit processing data from satellites near the horizon. I believe I set those to 10 or 15 degrees.
The Symmetricom 58532A antenna does use a patch element and does not need the cone-shaped radome to provide space for a quadrifiliar element. That cone shape must be entirely for environmental reasons for it surely adds cost to the antenna. Snow release? Beats me! There is snow atop Matterhorn Mountain in nearby Disneyland but non falls here...
Larry
Usually GPS antennas are patch antennas. The PROCOM GPS4 (I have 2 of
them) should be a real QFH (I haven't opened it to verify), the
Vaisala radiosonde RS92 has a real QFH. The Sarantel SL series seem is
a double helix not a classic QFH with the two different-size loops.
They name their series GeoHelix.
<https://www.datamatik.no/media/produkt/gps-4.pdf>
<https://www.wmo.int/pages/prog/www/IMOP/meetings/Upper-Air/Systems-Intercomp/Doc3-4(1)Vaisala.pdf>
<http://www.wless.ru/files/Accessaries/Antenna/sl1200%20product%20spec%20v7_1210.pdf>
...
--
Best wishes,
Larry McDavid W6FUB
Anaheim, California (SE of Los Angeles, near Disneyland)
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Bob kb8tq
2018-05-12 21:16:10 UTC
Permalink
Hi

As mentioned a number of times, quadrafilar antennas were only popular for a very short
while back in the 1980’s. Once people started using GPS for “stuff” they rapidly lost out in
the antenna race. They were made popular by an early NIST paper. Later on NIST effectively
said “oops !!” in reference to that paper.

So yes, any modern GPS antenna is likely to be a patch antenna. Trimble and Novatel both
have “exotic” antennas, but they still are fundamentally a patch.

Why all of this? Multi-path. You want to *reject* signals close to the horizon since they are
the ones most likely to be distorted by reflections. Indeed choke rings and the various other
exotic approaches are all aimed at multiparty rejection by reducing gain at (or below) the horizon.

Bob
I recently had an unexpected failure of a white-conical-dome HP/Symmetricom 58532A GPS antenna that had been in-place about 5 feet above the roof of my two-story home in Southern California for about ten years. I have two similar GPS antennas located about ten feet apart on this roof, one fed with about 50 feet of Andrews Heliax and the other with LMR400; the other antenna continued to work ok. The antennas feed 4x and 8x amplified GPS Source (brand name) antenna splitters. I noticed the failure when several GPSDO units and a GPS Clock failed to sync with the GNSS. I confirmed the failure was not the antenna splitter and I replaced the failed GPS antenna one of the same type, after which all returned to normal.
I removed the conical radome from the failed antenna and was surprised to find the antenna element was actually a patch, not the quadrafilar I expected under that conical dome. Subsequently I opened the radomes of three other similar GPS timing antennas made by various manufacturers and found that all use patch antennas. I had believed these timing antennas used a quadrafilar design to benefit from higher low-angle gain.
So, it appears the conical radome shape is really only to prevent snow accumulation. Well... from my experience here on the flatlands of Anaheim near Disneyland, that seems to be completely effective as I've surely had no snow buildup! :) But, I had surely expected the conical radome covered a quadrafilar antenna. Am I alone in expecting a quadrafilar antenna?
Further troubleshooting of this failed antenna revealed many discrete components on the underside of the round board holding the patch antenna. The circuit uses a three-stage gain amplifier with three Toko bandpass filters, numerous bypass capacitors and stripline inductors. Probing the circuit with a sig gen and spectrum analyzer showed that all three gain stages were working about as expected. Of course, even with 26-30 dB gain in the antenna, the SA did not have enough gain nor low enough noise floor to see any GPS signal from the antenna. But, each gain stage seemed to be working ok. So, what was the failure?
Upon removing the radome, one unexpected thing was seen. The construction uses a short coax cable up from the N connector, through a hole in the circuit board, where it is bent over and finally soldered to circuit board pads for the shield and center conductor. There was a great deal of very dark flux residue around this coax solder connection. The appearance was so bad it even looked like a cracked solder joint, though that proved not to be the case when the flux residue was thoroughly removed. It did not occur to me to functionally test the antenna at this point. Later, it was necessary to unsolder this coax so the board could be removed to access the components on the underside for detailed testing. But, stage-by-stage RF gain testing did not reveal any problems, so the antenna was reassembled for actual field testing.
The result? The antenna now works ok; locking sync to the GPS GNSS. I gotta conclude the flux residue was attenuating the signal out of the antenna. Careful inspection of that coax solder joint absolutely did not show any problem after the flux was removed so I believe continuity was ok.
I next removed the radome from one of my (new) Symmetricom antennas to inspect its coax solder joint and discovered this (perhaps newer) version has a metal shield-can soldered over the coax solder pads; I am loathe to remove that shield just to inspect the solder joint flux. However, there is no flux evident on the solder tabs where the metal shield-can is soldered to the circuit board so the whole thing must have been defluxed after soldering. That would be a better process anyway.
To make this very long story into a short one, I learned that the HP/Symmetricom 58532A GPS Reference (timing) antennas use a simple patch antenna instead of a quadrafilar antenna and that old solder flux residue will attenuate the even amplified GPS signal out of this antenna.
I welcome your constructive comments.
--
Best wishes,
Larry McDavid W6FUB
Anaheim, California (SE of Los Angeles, near Disneyland)
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Larry McDavid
2018-05-13 00:38:59 UTC
Permalink
Thanks, Dave, for reporting your failed GPS antenna; at least, I am not
alone in having this failure.

It will be interesting to understand what you find when you open your
failed 58532A. Removing the radome is very easy, just 4 screws and some
wiggling or gentle prying. If yours does not have the metal shield-can
over the coax termination, a quick look at the coax solder joints for
old flux will confirm or refute that as the likely failure cause. If
your antenna has the shield-can and you see no flux around its soldered
tabs, there likely is no flux problem.

Perhaps 1-2 years ago Symmetricom offered here a deep discount on this
antenna, clearing their stock; presumably they have something newer. The
antennas with the shield-can are from my purchase from Symmetricom of
several of these antennas. The 58532A that failed is at least 10 years
old so they must have made an in-line design change without changing the
part number.

If you do remove the PWB, you will find the RF circuit rather obvious
and even rectilinear in layout. All the parts are SMT. Two of the three
amplifier chips are the same, as are two of the three bandpass filters.
The first amplifier and the first bandpass filter are unique.

My primary goal in writing this narrative was to help someone who also
had a similar antenna failure. I've heard now from several who have. If
the fix is as simple as old flux removal, the antennas can probably be
salvaged.

When I first tested the repaired antenna, I used a 5 vdc GPS device and
that was successful. Later, I used another GPS device that puts only 3.3
vdc to the antenna and that worked ok also, with no noticeable
difference in performance. Note that the Symmetricom spec rates the
antenna at 5 vdc input.

Larry W6FUB
Larry
Thanks for the analysis... I too have a failed 58532A which died  a year
ago . which I had not bothered to disassemble yet..The weather guessers
are predicting rain all week net week so maybe I will find an
opportunity to comp[are my findings to yours
Do you have a schematic for the board or is the layout so simple that it
is self evident once you look at the board?
Stay tuned for film at 11
-DC
de NR1DX
I recently had an unexpected failure of a white-conical-dome
HP/Symmetricom 58532A GPS antenna......
--
Best wishes,

Larry McDavid W6FUB
Anaheim, California (SE of Los Angeles, near Disneyland)
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Larry McDavid
2018-05-13 20:35:50 UTC
Permalink
I can't be completely certain the residual and ugly flux residue in my
Symmetricom GPS antenna was the cause of the antenna failure. I can say
that, after cleaning off the flux residue, the antenna worked again.

I did fail to explain that after verifying the GPS antenna splitter was
not the cause of signal failure, I verified the Symmetricom antenna was
getting 5 vdc power and also that the antenna was drawing about 20 mA
current from the 5 vdc source. That 20 mA is about right for this
Spectracom antenna, according to its spec. The 20 mA also indicates
there was no short or open circuit to the antenna. That surely suggests
to me that the antenna amplifier circuitry had no gross failure.

I worked in the precision scientific instrumentation design field for
over 40 years and I can't count the number of times flux and whisker
growth has caused problems in circuitry and connectors. I may be
old-fashioned but I still believe the best solder flux is a flux you
later completely remove!

Spectracom apparently agrees because they, in later versions of this
same antenna, added a shield over the coax termination and totally
removed all residual flux.

Larry
Flux can provide just the right kind of ionic leakage path that leads to
whisky growth
and eventual sudden shorts.
Dana
To make this very long story into a short one, I learned that the HP/
Symmetricom 58532A GPS Reference (timing) antennas use a simple patch
antenna instead of a quadrafilar antenna and that old solder flux
residue
will attenuate the even amplified GPS signal out of this antenna.
Flux seems unlikely to produce a sudden failure.
If flux was the problem, I'd expect it to work poorly when first
installed,
or maybe decay slowly over time as something changed.
...
--
Best wishes,

Larry McDavid W6FUB
Anaheim, California (SE of Los Angeles, near Disneyland)
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Hal Murray
2018-05-14 01:42:41 UTC
Permalink
I can't count the number of times flux and whisker growth has caused
problems in circuitry and connectors.
A whisker might explain things. Would that also show up as over-current?
So there are 3D quadrifiliar GPS antennas..
This photo is from 2009:
Loading Image...

That's from a Lucent KS-24019L112A.

A Maxrad antenna, PN: Z3001, has the same shape, tan top with similar insides.

Another one from, Pctel, GPS-TMG-HR-26N, has a slightly larger cylinder.
It has a metal base plate.

Motorla, AN25090031, shorter and wider has a patch.
NAIS, CCAH32ST04, has a patch.
--
These are my opinions. I hate spam.



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Larry McDavid
2018-05-14 15:19:18 UTC
Permalink
Usually, in electronics, when we hear about "whiskers" we think of tin
whisker growth. That is surely real but not all whiskers are tin. In
fact, some whiskers are organic rather than metallic; sometimes these
are even somewhat semi-conducting. Such conductance paths lead to very
confusing troubleshooting results!

Rosin solder flux, RA (Rosin Activated) or RMA (Rosin Mildly Activated),
contains organics that aggressively clean oxides from PWB pads and metal
leads of components. This activated flux is actually corrosive and will
often do strange things if left in place. It used to be that this flux
was removed by vapor-phase TCE cleaning but that chemical got into
ground water and is no longer used for flux cleaning. But, there are
aqueous saponifiers that can clean rosin flux effectively.

Often, the final water rinse from assembled PWB cleaning is checked for
conductance, even high ohmic conductance, and cleaning not deemed
complete until this test is passed. Leaving activated rosin solder flux
on an assembled PWB is a really bad thing to do.

I don't know what was in the dark brown flux residue I found on my
Symmetricom antenna board, but it should not have been there. It would
not have produced tin whisker growth but it could easily have produced
other conductance paths across the soldered coax pads. Those could have
been RF paths and not have caused higher dc current draw by the antenna.

Again, I can't be certain the flux residue caused my GPS antenna
failure, but I believe it very likely and that is supported by the end
result of fixing the antenna.

Unless someone has something new to add, surely we have beaten this
topic to death. I was only trying to help others who might have a
similar GPS antenna failure.

Larry
Post by Hal Murray
I can't count the number of times flux and whisker growth has caused
problems in circuitry and connectors.
A whisker might explain things. Would that also show up as over-current?
...
--
Best wishes,

Larry McDavid W6FUB
Anaheim, California (SE of Los Angeles, near Disneyland)
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Van Horn, David
2018-05-14 16:56:26 UTC
Permalink
There's a great article out there on the web. It takes a bit of digging, but the title is "Low voltage, the incompetent ignition source".
They discuss fires on PCBs caused by trace contaminants and dendrite growth. A PCB with sustained flame is shown, powered by a lithium coin cell.


-----Original Message-----
From: time-nuts <time-nuts-***@febo.com> On Behalf Of Larry McDavid
Sent: Monday, May 14, 2018 9:19 AM
To: Time-Nuts Mail List <time-***@febo.com>
Subject: Re: [time-nuts] GPS Timing Antenna Failure - Long

Usually, in electronics, when we hear about "whiskers" we think of tin whisker growth. That is surely real but not all whiskers are tin. In fact, some whiskers are organic rather than metallic; sometimes these are even somewhat semi-conducting. Such conductance paths lead to very confusing troubleshooting results!

Rosin solder flux, RA (Rosin Activated) or RMA (Rosin Mildly Activated), contains organics that aggressively clean oxides from PWB pads and metal leads of components. This activated flux is actually corrosive and will often do strange things if left in place. It used to be that this flux was removed by vapor-phase TCE cleaning but that chemical got into ground water and is no longer used for flux cleaning. But, there are aqueous saponifiers that can clean rosin flux effectively.

Often, the final water rinse from assembled PWB cleaning is checked for conductance, even high ohmic conductance, and cleaning not deemed complete until this test is passed. Leaving activated rosin solder flux on an assembled PWB is a really bad thing to do.

I don't know what was in the dark brown flux residue I found on my Symmetricom antenna board, but it should not have been there. It would not have produced tin whisker growth but it could easily have produced other conductance paths across the soldered coax pads. Those could have been RF paths and not have caused higher dc current draw by the antenna.

Again, I can't be certain the flux residue caused my GPS antenna failure, but I believe it very likely and that is supported by the end result of fixing the antenna.

Unless someone has something new to add, surely we have beaten this topic to death. I was only trying to help others who might have a similar GPS antenna failure.

Larry
Post by Hal Murray
I can't count the number of times flux and whisker growth has
caused problems in circuitry and connectors.
A whisker might explain things. Would that also show up as over-current?
...
--
Best wishes,

Larry McDavid W6FUB
Anaheim, California (SE of Los Angeles, near Disneyland) _______________________________________________
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Larry McDavid
2018-05-14 21:55:12 UTC
Permalink
The article referenced below by David is really good and really scary!

The article can be downloaded but requires that you identify yourself so
they can send by email a link to download the article. Look here and
read down the list to the sixth article available for download:

https://foresiteinc.com/resources/

Look for the article titled, "Low Voltage, the Incompetent Ignition
Source – Dispelling the Myth."

While this article is focused on problems resulting from use of no-clean
solder fluxes commonly used today, note that activated rosin fluxes, if
not thoroughly cleaned after soldering, leave the activation chemicals
on the board.

Larry
Post by Van Horn, David
There's a great article out there on the web. It takes a bit of digging, but the title is "Low voltage, the incompetent ignition source".
They discuss fires on PCBs caused by trace contaminants and dendrite growth. A PCB with sustained flame is shown, powered by a lithium coin cell....
--
Best wishes,

Larry McDavid W6FUB
Anaheim, California (SE of Los Angeles, near Disneyland)
--
Best wishes,

Larry McDavid W6FUB
Anaheim, California (SE of Los Angeles, near Disneyland)
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