[time-nuts] Re: GPS failed

[John Ackermann]

Hi Skipp -- there is a lot of info about interference mitigation in the u-blox integration manual for the ZED--F9T (available under the docs at https://www.u-blox.com/en/product/zed-f9t-module).  It might give you some clues, and I think might also point to another u-blox app note on the topic.

Most of the antennas I've seen that have an LNA also include a SAW filter.  I also once found on either Amazon or eBay so e new-product, relatively inexpensive, high pass filters with cutoff around 1 GHz.  Those would help knock down broadcast, trunking, etc. stuff.  (But of course nothing will help with on-frequency crud coming from outside the GPS system.)

John

On Jul 11, 2022, 8:49 AM, at 8:49 AM, skipp Isaham via time-nuts <time-nuts at lists.febo.com> 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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