[time-nuts] Important parameters for a GPS/GNSS antenna

Tommy phone tholmes at woh.rr.com
Thu May 7 14:16:01 EDT 2015


I'm curious whether it would need 360 degree rotation? Would simply cycling about 120 degrees on the end of a short arm be just as good and could be done without a rotary joint? I understand that now the RX is moving but within a small radius would it be unbearable? Or would 300 degrees around the axis be sufficient?

From Tom Holmes, N8ZM


> On May 7, 2015, at 11:49 AM, John Ackermann N8UR <jra at febo.com> wrote:
> 
> Just put the GPS antenna, receiver, battery, and a low power RF transmitter modulated by the PPS (wide bandwidth = fast edge time) on the turntable, then use an appropriate receiver to demodulate the PPS and feed it to the rest of the system.  Put the RX antenna directly above (or below) the turntable so the path length remains close to constant.  Using FM might also remove Doppler effects from the received pulse.
> 
> On 5/7/2015 11:18 AM, Tom Van Baak wrote:
>>>> I wonder if anybody ever made a rotating GPS antenna to average out the
>>>> X-Y phase-center offset ?
>> 
>>> Of course, this does not really work with a gps antenna, unless you
>>> put the whole receiver onto the rotary table. But then you shift
>>> the problem onto the PPS output (note: amplitude noise translates
>>> into phase noise).
>> 
>> Attila,
>> 
>> My thought was to put PHK's proposed experiment entirely on the rotating table: antenna, receiver, local Cs standard, laptop, and battery. You could also get interesting data if you slightly offset the antenna from the center. It would make the ultimate GPS Spirograph. (for those of you under 40, http://en.wikipedia.org/wiki/Spirograph will explain)
>> 
>> /tvb
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