Re: [time-nuts] GPS Timing Antenna Failure - Long

[Larry McDavid]

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



On 5/14/2018 9:56 AM, Van Horn, David wrote:

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

Re: [time-nuts] GPS Timing Antenna Failure - Long

[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.


-Original Message-
From: time-nuts <time-nuts-boun...@febo.com> On Behalf Of Larry McDavid
Sent: Monday, May 14, 2018 9:19 AM
To: Time-Nuts Mail List <time-nuts@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



On 5/13/2018 6:42 PM, Hal Murray wrote:
> 
>>   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) 
___
time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to 
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] GPS Timing Antenna Failure - Long

[Larry McDavid]

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



On 5/13/2018 6:42 PM, Hal Murray wrote:



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

Re: [time-nuts] GPS Timing Antenna Failure - Long

[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?


> So there are 3D quadrifiliar GPS antennas..

This photo is from 2009:
  http://users.megapathdsl.net/~hmurray/time-nuts/Lucent-Antenna.jpg

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.



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

Re: [time-nuts] GPS Timing Antenna Failure - Long

[Bob kb8tq]

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

> On May 13, 2018, at 4:53 PM, Larry McDavid  wrote:
> 
> 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
> 
> 
> 
> On 5/13/2018 5:20 AM, Azelio Boriani wrote:
>> 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.
>> 
>> 
>> 
>> ...
> 
> -- 
> Best wishes,
> 
> Larry McDavid W6FUB
> Anaheim, California  (SE of Los Angeles, near Disneyland)
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

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

Re: [time-nuts] GPS Timing Antenna Failure - Long

[Larry McDavid]

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



On 5/13/2018 5:20 AM, Azelio Boriani wrote:

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.




...


--
Best wishes,

Larry McDavid W6FUB
Anaheim, California  (SE of Los Angeles, near Disneyland)
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] GPS Timing Antenna Failure - Long

[Larry McDavid]

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


On 5/13/2018 4:15 AM, Dana Whitlow wrote:

Flux can provide just the right kind of ionic leakage path that leads to
whisky growth
and eventual sudden shorts.

Dana


On Sun, May 13, 2018 at 12:23 AM, Hal Murray 
wrote:



lmcda...@lmceng.com said:

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

Re: [time-nuts] GPS Timing Antenna Failure - Long

[Azelio Boriani]

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.





On Sun, May 13, 2018 at 1:25 PM, Clint Jay  wrote:
> I'm all for anything that encourages whisky growth
>
> On Sun, 13 May 2018 12:16 pm Dana Whitlow,  wrote:
>
>> Flux can provide just the right kind of ionic leakage path that leads to
>> whisky growth
>> and eventual sudden shorts.
>>
>> Dana
>>
>>
>> On Sun, May 13, 2018 at 12:23 AM, Hal Murray 
>> wrote:
>>
>> >
>> > lmcda...@lmceng.com said:
>> > > 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.
>> >
>> >
>> >
>> > ___
>> > time-nuts mailing list -- time-nuts@febo.com
>> > To unsubscribe, go to https://www.febo.com/cgi-bin/
>> > mailman/listinfo/time-nuts
>> > and follow the instructions there.
>> >
>> ___
>> time-nuts mailing list -- time-nuts@febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] GPS Timing Antenna Failure - Long

[Clint Jay]

I'm all for anything that encourages whisky growth

On Sun, 13 May 2018 12:16 pm Dana Whitlow,  wrote:

> Flux can provide just the right kind of ionic leakage path that leads to
> whisky growth
> and eventual sudden shorts.
>
> Dana
>
>
> On Sun, May 13, 2018 at 12:23 AM, Hal Murray 
> wrote:
>
> >
> > lmcda...@lmceng.com said:
> > > 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.
> >
> >
> >
> > ___
> > time-nuts mailing list -- time-nuts@febo.com
> > To unsubscribe, go to https://www.febo.com/cgi-bin/
> > mailman/listinfo/time-nuts
> > and follow the instructions there.
> >
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] GPS Timing Antenna Failure - Long

[Dana Whitlow]

Flux can provide just the right kind of ionic leakage path that leads to
whisky growth
and eventual sudden shorts.

Dana


On Sun, May 13, 2018 at 12:23 AM, Hal Murray 
wrote:

>
> lmcda...@lmceng.com said:
> > 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.
>
>
>
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts
> and follow the instructions there.
>
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] GPS Timing Antenna Failure - Long

[Hal Murray]

lmcda...@lmceng.com said:
> 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.



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

Re: [time-nuts] GPS Timing Antenna Failure - Long

[Larry McDavid]

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


On 5/12/2018 3:17 PM, Artek Manuals wrote:

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
manu...@artekmanuals.com

On 5/12/2018 4:07 PM, Larry McDavid wrote:
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)
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] GPS Timing Antenna Failure - Long

[Bob kb8tq]

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

> On May 12, 2018, at 4:07 PM, Larry McDavid  wrote:
> 
> 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 

[time-nuts] GPS Timing Antenna Failure - Long

[Larry McDavid]

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