[time-nuts] Re: GPS failed

[Mark Spencer]

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

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From: Bob kb8tq<mailto:kb8tq at n1k.org>
Sent: July 12, 2022 11:19 AM
To: Discussion of precise time and frequency measurement<mailto:time-nuts at lists.febo.com>
Cc: Mark Spencer<mailto:markspencer at 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 at 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 at 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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>>
>>
>>
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