GPS failed
Hi
The “typical” Symmetricom cone shaped GPS antennas are targeted at
cell phone tower applications. Being mounted on the same structure
as multiple cell transmitters puts them in a significant RF environment.
They have a lot of filtering built into the antenna to try to prevent overload
issues.
As with a lot of things, Symmetricom simply rebrands antennas made by
others. Not all cone shaped antennas are identical. However it’s a pretty
good bet that most of them are very similar to what Symmetericom ( and
the other folks ) supply for cell applications.
The “other end” of the range are the multi band saucer shaped “survey”
antennas. They tend to have a lot less filtering and be more focused at
allowing the user to access a wide range of frequencies ( both GNSS and
supplemental services) via a single device. Lots of filtering also tends to
mess up delay here or there, that’s not a great thing for high precision
work.
Bob
On Jul 12, 2022, at 9:39 AM, Mark Spencer via time-nuts time-nuts@lists.febo.com wrote:
For what it is worth...
I have a commercial grade ( Symmetricom ?) GPS antenna on the roof of my home. I don't recall ever having any issues with GPS reception despite having / had various other transmit / receive antennas on the roof for various frequencies from 1.8 MHz thru 1.3 GHz. Power levels on some bands (not including 1.2 GHz thru 1.3 GHz where I have never exceeded approx 10 watts) can equal or occasionally exceed 100 watts.
As far as I know all my GPS receivers are using the typical 1.5 GHz GPS band.
As usual the experiences of others may differ from mine.
Best regards
Mark Spencer
On Jul 12, 2022, at 12:08 AM, Matthias Welwarsky via time-nuts time-nuts@lists.febo.com wrote:
Hi,
if you're worried about in-band interference, the 23cm HAM radio band is
reasonably close to the L1 GPS frequency. When I was still active in packet
radio back in the days, our digipeater DB0DAR lost an interlink due to
interference with a precision GPS receiver in use by another university
institute. We had to shut it down. I think they operated a DGPS site at the
time and our link traffic caused errors in the correction data. Or something.
BR,
Matthias
On Montag, 11. Juli 2022 01:19:18 CEST skipp Isaham via time-nuts wrote:
Hello to the Group,
I'd like to get some opinions and war stories regarding GPS reliability at
high RF level and elevation locations.
Background: Three different hill-top GPS receivers, all different types,
using different antennas mounted on an outside fixiture, plain view of the
open sky, all stopped working.
Test antennas were brought in and placed on a fixture well away from the
original antennas, the recevers went back in to capture and lock.
From what I understand, the original antennas are what I would call straight
preamp with no pre-selection / filtering.
The ordered and now inbound replacements are said to contain a SAW filter
system. It is the intent of the client to just place these "improved
antennas" in to service and get on with life.
I would suspect a GPS antenna (and receiver) could be subject to RF overload
or blocking, however, we're assuming nothing major has changed at the site,
nor any nearby location. One might think there are more GPS receivers
being pushed out of reliable operation by the world around them, I'm just
not hearing those stories from a lot of people using them (GPS receivers).
Any new install GPS receiver antenna ordered will/should contain some
pre-selection to potentially avoid a problem, even some years down the
road? Seems like that's where things are going... no more off the shelf,
wide band, (hot) preamplified GPS antennas in busy locations?
Thank you in advance for any related comments and/or opions ...
cheers,
skipp
skipp025 at jah who dot calm
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Thanks Bob.
I believe this is what I have (I would need to climb up on the roof to double check the part number (assuming the label is still legible..))
https://www.microsemi.com/document-portal/doc_view/133381-58532a-datasheet
Best regards
Mark Spencer
Sent from Mailhttps://go.microsoft.com/fwlink/?LinkId=550986 for Windows
From: Bob kb8tqmailto:kb8tq@n1k.org
Sent: July 12, 2022 11:19 AM
To: Discussion of precise time and frequency measurementmailto:time-nuts@lists.febo.com
Cc: Mark Spencermailto:markspencer@outlook.com
Subject: Re: [time-nuts] GPS failed
Hi
The “typical” Symmetricom cone shaped GPS antennas are targeted at
cell phone tower applications. Being mounted on the same structure
as multiple cell transmitters puts them in a significant RF environment.
They have a lot of filtering built into the antenna to try to prevent overload
issues.
As with a lot of things, Symmetricom simply rebrands antennas made by
others. Not all cone shaped antennas are identical. However it’s a pretty
good bet that most of them are very similar to what Symmetericom ( and
the other folks ) supply for cell applications.
The “other end” of the range are the multi band saucer shaped “survey”
antennas. They tend to have a lot less filtering and be more focused at
allowing the user to access a wide range of frequencies ( both GNSS and
supplemental services) via a single device. Lots of filtering also tends to
mess up delay here or there, that’s not a great thing for high precision
work.
Bob
On Jul 12, 2022, at 9:39 AM, Mark Spencer via time-nuts time-nuts@lists.febo.com wrote:
For what it is worth...
I have a commercial grade ( Symmetricom ?) GPS antenna on the roof of my home. I don't recall ever having any issues with GPS reception despite having / had various other transmit / receive antennas on the roof for various frequencies from 1.8 MHz thru 1.3 GHz. Power levels on some bands (not including 1.2 GHz thru 1.3 GHz where I have never exceeded approx 10 watts) can equal or occasionally exceed 100 watts.
As far as I know all my GPS receivers are using the typical 1.5 GHz GPS band.
As usual the experiences of others may differ from mine.
Best regards
Mark Spencer
On Jul 12, 2022, at 12:08 AM, Matthias Welwarsky via time-nuts time-nuts@lists.febo.com wrote:
Hi,
if you're worried about in-band interference, the 23cm HAM radio band is
reasonably close to the L1 GPS frequency. When I was still active in packet
radio back in the days, our digipeater DB0DAR lost an interlink due to
interference with a precision GPS receiver in use by another university
institute. We had to shut it down. I think they operated a DGPS site at the
time and our link traffic caused errors in the correction data. Or something.
BR,
Matthias
On Montag, 11. Juli 2022 01:19:18 CEST skipp Isaham via time-nuts wrote:
Hello to the Group,
I'd like to get some opinions and war stories regarding GPS reliability at
high RF level and elevation locations.
Background: Three different hill-top GPS receivers, all different types,
using different antennas mounted on an outside fixiture, plain view of the
open sky, all stopped working.
Test antennas were brought in and placed on a fixture well away from the
original antennas, the recevers went back in to capture and lock.
From what I understand, the original antennas are what I would call straight
preamp with no pre-selection / filtering.
The ordered and now inbound replacements are said to contain a SAW filter
system. It is the intent of the client to just place these "improved
antennas" in to service and get on with life.
I would suspect a GPS antenna (and receiver) could be subject to RF overload
or blocking, however, we're assuming nothing major has changed at the site,
nor any nearby location. One might think there are more GPS receivers
being pushed out of reliable operation by the world around them, I'm just
not hearing those stories from a lot of people using them (GPS receivers).
Any new install GPS receiver antenna ordered will/should contain some
pre-selection to potentially avoid a problem, even some years down the
road? Seems like that's where things are going... no more off the shelf,
wide band, (hot) preamplified GPS antennas in busy locations?
Thank you in advance for any related comments and/or opions ...
cheers,
skipp
skipp025 at jah who dot calm
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To unsubscribe send an email to time-nuts-leave@lists.febo.com
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Sent from my Phone
On 13 Jul 2022, at 02:34, Bob kb8tq via time-nuts time-nuts@lists.febo.com wrote:
Hi
The “typical” Symmetricom cone shaped GPS antennas are targeted at
cell phone tower applications. Being mounted on the same structure
as multiple cell transmitters puts them in a significant RF environment.
They have a lot of filtering built into the antenna to try to prevent overload
issues.
As with a lot of things, Symmetricom simply rebrands antennas made by
others. Not all cone shaped antennas are identical. However it’s a pretty
good bet that most of them are very similar to what Symmetericom ( and
the other folks ) supply for cell applications.
The “other end” of the range are the multi band saucer shaped “survey”
antennas. They tend to have a lot less filtering and be more focused at
allowing the user to access a wide range of frequencies ( both GNSS and
supplemental services) via a single device. Lots of filtering also tends to
mess up delay here or there, that’s not a great thing for high precision
work.
Bob
Bob,
That was true 10-15 years ago. Good quality surveying antennas often has quite decent filtering on each band they are designed for.
/Björn
Hi
On Jul 13, 2022, at 6:50 AM, Björn via time-nuts time-nuts@lists.febo.com wrote:
Sent from my Phone
On 13 Jul 2022, at 02:34, Bob kb8tq via time-nuts time-nuts@lists.febo.com wrote:
Hi
The “typical” Symmetricom cone shaped GPS antennas are targeted at
cell phone tower applications. Being mounted on the same structure
as multiple cell transmitters puts them in a significant RF environment.
They have a lot of filtering built into the antenna to try to prevent overload
issues.
As with a lot of things, Symmetricom simply rebrands antennas made by
others. Not all cone shaped antennas are identical. However it’s a pretty
good bet that most of them are very similar to what Symmetericom ( and
the other folks ) supply for cell applications.
The “other end” of the range are the multi band saucer shaped “survey”
antennas. They tend to have a lot less filtering and be more focused at
allowing the user to access a wide range of frequencies ( both GNSS and
supplemental services) via a single device. Lots of filtering also tends to
mess up delay here or there, that’s not a great thing for high precision
work.
Bob
Bob,
That was true 10-15 years ago. Good quality surveying antennas often has quite decent filtering on each band they are designed for.
Quite true of the stuff we pay $2K for. The eBay surplus or the $100 antennas
from China …. I’m not so sure of.
Bob
/Björn
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