[time-nuts] Choke Ring Design for L1

[Bruce Griffiths]

WarrenS wrote:
>> Bruce wrote:
> <ws response
>
>> Only for your particular location and antenna.
> <True, My location is under the sky indoors or outdoors, and I used 
> severl cheap car type antennas and a pole mounted timing antenna.
> May not work as well in other locations or with other types of 
> antennas. (Like under the water or with choke antennas)
>
>> You have no actual idea of how the antenna response is affected by 
>> the presence of the cake tin,
> <Sure I do, You have not been keeping up with the latest Lady Heather 
> updates, Take a look at her new antenna plot capability.
>
Those plots give little information about the antenna response to 
variations in SV elevation directly as the signal strength from the SV 
also varies with elevation.
>> nor did you specify what sort of antenna you are using with it.
> <Yes I did give a recommendation in the beginning for a timing antenna,
> but I get the same kind of effect on all "car" type also.
> (which is no surprise case they are made to be mounted on a metal body.)
>
The latter are all patch antennas which don't work at all well without a 
ground plane (either an external one or a built in one).
Even the thickness of the ground plane makes a difference to the antenna 
response:

http://www.emtalk.com/tut_1.htm

http://www.orbanmicrowave.com/The_Basics_Of_Patch_Antennas.pdf

http://www.specemc.com/patch.asp

http://piers.mit.edu/piersproceedings/download.php?file=cGllcnMyMDA5bW9zY293fDVQNV8xOTI2LnBkZnwwOTAzMTQwODAxMzA=

http://ctvr.ie/docs/RF%20Pubs/IEEEVTC_2007_Investigation%20on%20Miniature%20Wideband%20Patch%20Antenna%20.pdf

http://140.117.166.1/eehome/ISCOM2005/SubmitPaper/UploadPapers/ISCON05_00100.pdf

>> A patch antenna at the bottom of a cake tin may not have much gain 
>> over the elevation range of interest.
> <What I can say, It works good, and it is not likely it is the antenna 
> gain, cause by making a directly antenna out of it,
> cause I get some of the same effects with the pie pan turned the other 
> way.
>
>> Your explanation of why this appears to work well is still nonsense.
> <That is because I did not give one yet.  MY guess is that it is 
> blocking out multipath reflections of which I have many, and these 
> reflections tend to case dips in the signal level due to cancellations 
> as the sat moves across the sky. Also adds some gain to some antennas.
>
>> The variation in antenna response with elevation needs to be 
>> measured/calculated before one can safely conclude that such an antenna
> is universally useful.
> <READ answer AGAIN> That is exactly what I did with the new Lady 
> Heather, You may want to try it for yourself before your unfounded 
> criticizing or look at the attached.
>
>
No you didnt, no account is taken of the SV signal variation with elevation.
> ws
>
> ***************
> WarrenS wrote:
>> 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.
>>
> Only for your particular location and antenna.
> Your explanation of why this appears to work well is still nonsense.
>
> You have no actual idea of how the antenna response is affected by the
> presence of the cake tin, nor did you specify what sort of antenna you
> are using with it.
> A patch antenna (like your puck) at the bottom of a cake tin that just
> happens to be a quarter wave deep may not have much gain over the
> elevation range of interest.
>
> The variation in antenna response with elevation needs to be
> measured/calculated before one can safely conclude that such an antenna
> is universally useful.
>> 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
>> ***************
>> 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
>>>
>
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