Hi Tom:
When I was learning about the Trimble 1990 vintage Trimpack family of
receivers I bought a number of antennas and learned that the Trimpacks
need an antenna with about 40 dB of gain, which is a lot different from
a passive antenna or an active antenna with the more common 20 dB of gain.
http://www.pacificsites.com/~brooke/Trimpack.shtml#Ant
A passive antenna is good for use as a re-radiating antenna for indoor GPS.
I'm using a Motorola Timing antenna on a TV mast to get it above the
chimney closest to my radio room. But in order to get rid of the
multipath I've had to move the elevation mask up to the 50 or 60 degree
level. At lower elevation levels the standard deviation on TI
measurements gets much higher. I think that if a choke ring type
antenna was in the same position I could lower the elevation mask and
receive more satellites, thus enabling TRAIM, or getting better 1 PPS
signals. But the choke ring antennas are larger than the Timing antenna
and are not easily mounted to a TV antenna type mast (they want to see
pipe threads).
Have Fun,
Brooke
Tom Van Baak wrote:
Tom,
John A and I had a short antenna email earlier today, mostly about the
fact
that both of the GPS antennas we were using died.
I asked a question about certain "commercial" antennas which included the
Timing 2000, HP 58532A and the Datum 2640NW/DE, as to wether there were
any
opinions as to which is the better timing antenna. Neither of us has much
of an idea, do you have any thoughts?
Had
I've heard that many modern telecom GPS timing
antennas are heavily filtered since they are usually
placed in high RFI locations. This may be good for
them but I think it has negative side effects for the
kind of precise timing we do, so I'm told.
I'm going to ask Dr Clark to handle this one as he
understands GPS antennas very well. TAC -- what
I'd like to know is if patch is better than helix, if filtered
is better than unfiltered, how much amplification is
too much, vintage 1990's era antennas vs. 2005
antennas, real splitters vs. Radio Shack splitters,
antenna or preamp tempco issues, cable loss and
impedance issues, etc. At what ns level does a
groundplane start to matter. I guess what we need
is some kind of Time Nuts guide to surplus GPS
antennas.
If it's not possible to give a black and white answer
to what kind of antenna is best for a Z3801A-style
GPSDO, then at least, what are the factors that
make one better than another. And is any of this
simple to determine with experimentation? Maybe
we can all chip in and test a dozen antenna types
to find the answer or to confirm a prediction.
/tvb
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