The u-blox SAW filtering is great. We've carried out various RF
measurements with +40 dBm EIRP at 2.53 and 3.75 GHz with some u-blox
ANN-MB within <2m of the Tx antennas. While we haven't conducted
in-depth comparisons with a superior ground-truth, my current conclusion
is that the u-blox RTK performance is not (noticeably) affected by
strong out-of-band emissions. Without extensive filtering the Tx power
would likely steamroll any LNA/receiver. Of course, as John pointed out,
this won't help against in-band interference.
Best regards,
Carsten
On 11.07.22 15:16, John Ackermann via time-nuts wrote:
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
<[email protected]> 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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