[time-nuts] GPS Timing receivers

Brooke Clarke brooke at pacific.net
Thu Oct 6 22:08:08 EDT 2005

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. 

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,


Tom Van Baak wrote:

>>John A and I had a short antenna email earlier today, mostly about the
>>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
>>opinions as to which is the better timing antenna. Neither of us has much
>>of an idea, do you have any thoughts?
>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
>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.
>time-nuts mailing list
>time-nuts at febo.com

w/Java http://www.PRC68.com
w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml

More information about the time-nuts mailing list