[time-nuts] Choke Ring Design for L1

[WarrenS]

Thanks, Nice set of references as always.  
OK, so its not 100db, But you may of missed my point yet again.
If you think I said that a 10 cent pie pan is a good substitute for a $1000 survey antenna in all applications, 
I think we all know that would be Nonsense.

BUT what may not be known is:
that a turned up pie pan under my cheap patch/puck antenna, 
works about as good as an expensive survey antenna for use with a Tbolt GPSDO, 
That's not Nonsense, It's a tested fact.

So I'm not saying there is anything wrong with using a survey antenna on your GPSDO, 
if you have more money than cents, and you want the last sub ns of performance.
But it is not really necessary, there are many many ways to get more bang for the buck, 
and they would still need to be done first to take advantage of the survey antenna's small improvement when used for a GPSDO.  

There appears to be a false impression that choke rings remove all Multipath signals.
What they do is to remove multipath ground reflected signals from below the antenna, not multipath signals from above it. 

ws

***************
Bruce wrote:
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 doesn't 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
Bruce

*******************

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.
>
> 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
> ***************
> 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
>