This article discusses timing errors due to mismatch and multiple
reflections in transmissin lines:
http://www.dtic.mil/dtic/tr/fulltext/u2/a508044.pdf
Adrian
Edgardo Molina schrieb:
Dear Group,
Good evening. I just arrived home after the first day of conferences at the
Electrical Metrology Forum 2012 at Mexico's metrology center CENAM. I attended
several presentations of time and frequency, very interesting indeed. At last I
understood some concepts hard to land in theory. I will be attending the whole
week long and half of next week. I will have the pleasure and honour to meet
Dr. Judah Levine from NIST, who has shown a very nice attitude towards me and
accepted to talk a little bit around my thesis in network synchronization.
Now to the point if you kindly allow. I got involved in a round table
discussion around the use of GPS antennas for time and frequency GPS receivers.
I tried to make some points from my personal perspective. I got resistance from
the audience and the topic went hot very quickly and didn't set at the end.
Honestly I would like to share my doubts and opinions with you in order to
enhance my experience about the topic. In the end it could also be beneficial
to close this debate tomorrow while attending to CENAM's time and frequency
forum.
Facts and thoughts:
1. The time and frequency attendees at CENAM`s time and frequency forum is
reluctant to use GPS antenna splitters for a number of reasons I couldn't
conceive.
1.1 They argued that cross talk could happen among ports. I doubt it
with the newer models. I have experience with HP and Symmetricom units and they
state their products cancel cross talk.
1.2 They argued that there could be problems from the power feeding of
the antenna and mismatches at the receiver antenna port voltages. Again I doubt
it if one uses receivers in the same voltage range
2. I have been experimenting with GPS constellation coverage with different
brands of antennas. I have found different gains, different radiation patterns
and as a result different satellites in view for identical GPS receivers.
2.1 I have found that using a single antenna and a two port HP splitter
I get the same radiation pattern, gain and identical satellites in view for a
set of identical receivers. For comparison purposes I feel this is an adequate
scenario.
It is easier for me to take care of the transmission line length and
errors caused by phase differences, attenuation and delays.
2.2 Two identical GPS receivers each one with it's own antenna, could
eventually cause spatial diversity reception for a system of two receivers
conceptually set as one for comparison purposes. Different satellites being
tracked on
each receiver if not connected to a common antenna. Even if antennas
and transmission lines are identical.
Question is: Am I wrong doing the above mentioned assumptions while considering
the use of GPS transmission line splitters? I which scenarios are the splitters
recommended? In which cases they are rather not to be considered?
Better ask as to start buying more antennas or feel comfortable with my
original RF distribution design using splitters.
Your kind comments and expert advise is always welcome. Thank you!
Best regards,
Edgardo Molina
Dirección IPTEL
www.iptel.net.mx
T : 55 55 55202444
M : 04455 20501854
Piensa en Bits SA de CV
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