Discussion:
RF isolation requirements for multiple GPS receivers
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Dana Whitlow
2018-11-27 13:44:23 UTC
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I want to run about 4 separate GPS units of disparate
manufacture from a single antenna. My plan is to
provide power for the antenna via a bias tee (power
inserter) at the bottom end of the antenna's cable, then
use an isolating splitter on the receiver side of the bias
tee to split to the various receivers.

My question is: how much isolation between receivers
is likely to be necessary? Real life splitters are only
so-so in isolation performance (15-25 dB), and may
e significantly worse if the antenna's LNA's output is
a poor match. So I'm wondering if I'm going to need
more amplifiers in the splitter's outputs just for the sake
of adequate isolation between the GPS receivers.

Thanks,

Dana K8YUM
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Mike Cook
2018-11-27 14:16:36 UTC
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Hi,
I am using Mini-Circuits ZN4PD1-50+. They are about 30dB in the GPS frequency band. I hang 4 receivers each off three of these mixing Motorola, Ublox, Trimble and Navspark and never had an issue.
Mike
Post by Dana Whitlow
I want to run about 4 separate GPS units of disparate
manufacture from a single antenna. My plan is to
provide power for the antenna via a bias tee (power
inserter) at the bottom end of the antenna's cable, then
use an isolating splitter on the receiver side of the bias
tee to split to the various receivers.
My question is: how much isolation between receivers
is likely to be necessary? Real life splitters are only
so-so in isolation performance (15-25 dB), and may
e significantly worse if the antenna's LNA's output is
a poor match. So I'm wondering if I'm going to need
more amplifiers in the splitter's outputs just for the sake
of adequate isolation between the GPS receivers.
Thanks,
Dana K8YUM
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t***@timeok.it
2018-11-27 14:30:38 UTC
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Dana,
As described in the following HP GPS splitter the isolation is > 40dB.
https://www.febo.com/time-freq/gps/hp58516a/HP_58516A.pdf
I use one of these 8-channel splitters.
I had a bad experience using a passive splitter of the minicircuits in the 10MHz distribution in my lab.
An instrument that accidentally generated instead of receiving the reference disturbed all other related instruments.
In this case, an isolation of 25-30dB proved to be insufficient.
Therefore, I recommend using a GPS splitter with active components such as the classic HP models and other brands.
Luciano
www.timeok.it


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Data Tue, 27 Nov 2018 07:44:23 -0600
Oggetto [time-nuts] RF isolation requirements for multiple GPS receivers
I want to run about 4 separate GPS units of disparate
manufacture from a single antenna. My plan is to
provide power for the antenna via a bias tee (power
inserter) at the bottom end of the antenna's cable, then
use an isolating splitter on the receiver side of the bias
tee to split to the various receivers.

My question is: how much isolation between receivers
is likely to be necessary? Real life splitters are only
so-so in isolation performance (15-25 dB), and may
e significantly worse if the antenna's LNA's output is
a poor match. So I'm wondering if I'm going to need
more amplifiers in the splitter's outputs just for the sake
of adequate isolation between the GPS receivers.

Thanks,

Dana K8YUM
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and follow the instructions there.
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Bob kb8tq
2018-11-27 15:23:16 UTC
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Hi

I’ve run …. errr … lots ( > 40) of GPSDO’s on a common antenna with a single
amp and passive splitters. I’ve never seen any issues. That includes cases
with multiple ports un-terminated ( so not terrific isolation).

Bob
Post by Dana Whitlow
I want to run about 4 separate GPS units of disparate
manufacture from a single antenna. My plan is to
provide power for the antenna via a bias tee (power
inserter) at the bottom end of the antenna's cable, then
use an isolating splitter on the receiver side of the bias
tee to split to the various receivers.
My question is: how much isolation between receivers
is likely to be necessary? Real life splitters are only
so-so in isolation performance (15-25 dB), and may
e significantly worse if the antenna's LNA's output is
a poor match. So I'm wondering if I'm going to need
more amplifiers in the splitter's outputs just for the sake
of adequate isolation between the GPS receivers.
Thanks,
Dana K8YUM
_______________________________________________
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and follow the instructions there.
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