[time-nuts] Re: GPS failed

[Lux, Jim]

On 7/10/22 4:19 PM, 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).

yes, this happens.  We used to have a Pendulum timing receiver with a 
typical "small white cone" type amplified antenna - if someone was on 
the roof with a cellphone, it lost lock, presumably from the (way out of 
band) emissions.


As to where the interfering source is - it doesn't take much, and it 
could be some distance away.  After all, this was the big deal with 
LightSquared - it was moderately high powered terrestrial broadcast 
transmitters in the satellite downlink band next to GNSS.


>
> 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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