[time-nuts] Choke Ring Design for L1

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sun Mar 14 01:20:52 UTC 2010


WarrenS wrote:
>
> All true,
> BUT
> Just to keep from being mislead,
> I said what a choke ring antenna does,
> You have described how it is so good at its job.
>
> The Main purpose of the choke ring's, hi impedance, 1/4 wave, tuned 
> thingies, around the antenna is to keep reflected Signals from BELOW 
> the antenna from sneaking around into the antenna. It does not effect 
> the signals above the 10 deg or so elevation point.
> The choke rings are a necessary to get cm type survey accuracy,
> but a pie pan shield /ground plane pretty much does the same thing at 
> the GPSDO 1ns (1ft) level,
> where you don't need 100 db rejection for signals below the antenna.
>
Nonsense, a finite ground plane by itself has little effect on waves 
incident from underneath, unless of course its a resistive ground plane 
with just the right surface resistivity.
A choke ring antenna doesnt have anything like 100db rejection of 
multipath signals, the rejection varies with SV elevation.
http://www.javad.com/jns/index.html?/jns/technology/Choke%20Ring%20Theory.html

http://www.trimble.com/infrastructure/pdf/gnss-choke-ring-antenna_brochure.pdf

http://www.novatel.com/Documents/Papers/3D_choke_ring.pdf

http://www.weblab.dlr.de/rbrt/pdf/TN_0505.pdf

http://www.leica-geosystems.com/downloads123/zz/nrs/AR25/brochures/AR25_Brochure_en.pdf
> What I've found; don't even need to be lucky.
> Just put an 8 inch pie pan in the right place, facing the right 
> direction.
>
> ws
Bruce
> ***************
> Hi there,
>
> just to prevent from making mistakes ...
>
> You can have two different accessories for GNSS antennas:
> 1) a ground plane
>      it prevents the antenna from receiving signals from beneath the
>      antenna (from the ground, roof or whatever is beneath)
>      ... so this could be your pie pan normally
> 2) a choke ring
>      it creates an area of high impedance around your antenna;
>      because it is just a (set of) simple quarter wave waveguide(s) with
>      short-circuit on one end, you can build it from a sheet of metal by
>      yourself; you only need to calculate the sizes for your waveguide on
>      the L1 frequency ... and if you are a lucky guy and your pie pan 
> fits
>      these sizes, you probably can use it for that ;-)
>
> Best regards
>
> Martin
> ****************
>
>> Is there a design for a choke ring to add to my existing L1 GPS 
>> antenna ?
>
> Yeah
> If you are using it for GPSDO work where a ns is good enough and you 
> don't need cm accuracy,
> It is called a pie pan with its  Lip turned up.
> A choke rings blocks reflected signals from below the antenna from 
> effecting the signals, a pie pan works pretty good at that also.
> ws
>
> ***************
>> Hello The Net:
>
>> Is there a design for a choke ring to add to my existing L1 GPS 
>> antenna ?
>> While there may be some variations to the exact dimensions of a choke
>> ring to a specific type of L1 antenna, either patch, helical, etc.,
>> I suspect there is some commonality to the design dimensions.
>> I am looking to start construction and I will be using a cheapie
>> patch/puck antenna.
>
> Stan, W1LE
>
>
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