Discussion:
Terminators on empty outputs/connectors
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Clay Autery
2018-05-24 08:41:08 UTC
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Putting in a hardware order...

Question:  Is it recommended to put terminators on all unused GPS Distro
amp ports?  Output ports on GPSDO and NTP servers (10MHz and PPS).

Thanks!
--
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Clay Autery
MONTAC Enterprises
(318) 518-1389

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Dana Whitlow
2018-05-25 15:21:46 UTC
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I recommend putting terminators on unused ports, on general principles.
But I don't
think it would ordinarily be necessary to use big-bucks terms, unless the
distro amp is
really cheaply made.

If you have access to a VNA, it would be interesting to measure the complex
transmission
coefficient from input to one of the output ports while experimenting with
variations of
the number and locations of terminations for the other output ports. If
you find that none
of such manipulations have any visible effect, then you can probably skip
using terms
on unused ports. I should mention that any such measurements should best
be performed
at roughly the intended operating RF power level.

And for extra credit, report your findings to this discussion group.

Dana
Post by Clay Autery
Putting in a hardware order...
Question: Is it recommended to put terminators on all unused GPS Distro
amp ports? Output ports on GPSDO and NTP servers (10MHz and PPS).
Thanks!
--
______________________
Clay Autery
MONTAC Enterprises
(318) 518-1389
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ailman/listinfo/time-nuts
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Graham / KE9H
2018-05-25 15:33:28 UTC
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As usual, the answer is "it depends."

If the output is a single isolated output, then terminating load not
required, but no harm providing.

If the output is a multiple output, from a single driver, through a
resistive or transformer splitter, then the level stability on all ports
and the port to port isolation is dependent on the proper termination of
all ports.
So, if multiple 10 MHz or 1 pps outputs, terminations highly recommended.

--- Graham

==
Post by Dana Whitlow
I recommend putting terminators on unused ports, on general principles.
But I don't
think it would ordinarily be necessary to use big-bucks terms, unless the
distro amp is
really cheaply made.
If you have access to a VNA, it would be interesting to measure the complex
transmission
coefficient from input to one of the output ports while experimenting with
variations of
the number and locations of terminations for the other output ports. If
you find that none
of such manipulations have any visible effect, then you can probably skip
using terms
on unused ports. I should mention that any such measurements should best
be performed
at roughly the intended operating RF power level.
And for extra credit, report your findings to this discussion group.
Dana
Post by Clay Autery
Putting in a hardware order...
Question: Is it recommended to put terminators on all unused GPS Distro
amp ports? Output ports on GPSDO and NTP servers (10MHz and PPS).
Thanks!
--
______________________
Clay Autery
MONTAC Enterprises
(318) 518-1389
_______________________________________________
To unsubscribe, go to https://www.febo.com/cgi-bin/m
ailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
To unsubscribe, go to https://www.febo.com/cgi-bin/
mailman/listinfo/time-nuts
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Magnus Danielson
2018-05-26 09:55:03 UTC
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Hi,
Post by Clay Autery
Putting in a hardware order...
Question:  Is it recommended to put terminators on all unused GPS Distro
amp ports?  Output ports on GPSDO and NTP servers (10MHz and PPS).
Thanks!
All GPS splittes I have looked at so far uses the Wilkinson
power-splitter. It provides some isolations between the output ports, or
rather, the ideal scenario has perfect isolation, the real world not so
much naturally. If you consider a two-port splitter where you leave one
end open, and ignoring the fact that the splitter math actually wants a
50 ohm load to perform correctly, there will be some leakage over to the
next port and full leakage back to the source. Usually we can assume
that the source direction wave gets dampen in the amplifier sitting
there to compensate gain or for a passive one dampens in the cable back
and forth as well as not getting a perfect reflection in the antenna
source impedance. The direct leakage to the next port is likely to
dominate. Regardless, this will behave as multipath for the GPS signal
and just contribute to the multipath environment that the antenna
already have. It's only when you have a really crap splitter that you
need to be careful. For carrier phase measurements, you need to be more
careful about signals, but mostly for stability of signals.

So, for most cases, I don't bother on my splitters. I would only care if
I would really try to get stable and accurate measures, but not because
it would have much of an impact, but just because I don't want a simple
to fix thing do me any harm.

Cheers,
Magnus
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