[time-nuts] gps timing antennas

[Brian Kirby]

I put pictures out on the net years ago.  I put two rulers in the 
pictures to show folks the dimensions.  Back then we used the stock 
Motorola Antenna97, a patch antenna.

I have a set of the antennas stored.  When I get to the storage location 
this weekend, I will try to remember to shoot another set of pictures. 

As I recall, I found a common size aluminum cake pan set of 5 pans that 
came close to the needed choke ring dimensions.  The smallest pan was 
turned over and some of the rim was removed and the antenna was glued to 
it with epoxies.  Then then remaining pans were used face up and 
centered via a bolt.  I used some square aluminum tubing on the bottom 
to attach pipe clamps, and it was mounted to a pipe mount.  The other 
two sets that I have, are attached to adjustable laser level mounts, 
which is attached to surveying tripods.  I did some carrier phase 
surveying using the Motorola Oncore VP gps receivers and in general had 
positioning repeatability of just under 3/4 of an inch.

Of the bat, somewhere either NASA or NGS published data (on the web) on 
choke ring antennas back when choke rings first came out.  They had 
photos and measured dimensions and some performance data on the 
electrical phase centers/error on these antennas.  I believe the test 
were performed in Maryland, Virginia or DC area.

Also, I do not remember if it was on this list or the earlier TAPR list, 
it was discussed using the choke ring assembly off of a 3.7-4.2 Ghz 
satellite TVRO feedhorn assembly.  Choke rings can be wide bandwidth and 
low "Q" or narrow band and high "Q".

If Dr. Clark is still on the list, he may be able to enlighten everybody.

Brian KD4FM

WB6BNQ wrote:
> Hi Brian,
>
> Have you ever published your efforts with making the choke ring out of pie plates
> ?  If so do you have that available with, hopefully, pictures, deminsions and so
> forth ?  I have one of the Timing 2000 antennas.  Did you use the choke ring pie
> plate with it ?
>
> thanks,
>
> 73....Bill....WB6BNQ
>
> Brian Kirby wrote:
>
>   
>> The Motorola Timing 2000 and 3000 antennas are patch antennas.  They
>> have a pointed radome.  The have very little ground plane, which reduces
>> reception near the ground, which is desirable because of multipath
>> effects.    They also have quite a bit of filtering, so transmitting
>> antennas near the units, will not affect them.
>>
>> If you are not having a problem with multipath, a regular patch type
>> antenna probally from anybody should work well.
>>
>> If you are having multipath problems a timing antenna should help or a
>> choke ring assembly should help.  I have built choke rings out of pie
>> plates, and Dr. Tom Clark made a basic choke assembly using a common
>> electric junction box.
>>
>> I had problems with multipath because of mountains about 3/5 around my
>> location.  I changed the look angles so my receivers only receive above
>> 20 degrees above the horizon and I use timing antennas now.
>>
>> Brian KD4FM
>>
>> Matt Ettus wrote:
>>     
>>> Is there really anything in particular which is different about the
>>> antenna requirements of timing receivers as compared to ordinary
>>> high-quality receivers?  The timing antennas seem to be in pointy
>>> radomes, so that tells me they are probably quad-helixes rather than
>>> patch antennas.  How is that advantageous for timing in particular?
>>>
>>> Thanks,
>>> Matt
>>>
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