[time-nuts] Choke Ring Design for L1

[Bob Camp]

Hi

Some basic GPS math:

L1 is at: 

1575.42 MHz
190.5 mm wavelength
47.625 mm 1/4 wave
1.875 inch 1/4 wave

If you are after a 1/4 wave with a short at the bottom, starting from a 2" pan sounds like a good idea. Since you always have fringe effects, 1.875 probably isn't the point you get maximum benefit. Most of the people in the attached reference are running 2.5". I doubt that's because they got the math wrong....

For a true short at the bottom, you would have to do something about the pan bottoms really connecting well with each other. A "not quite short" at the bottom will give you a "not quite open" at the top. It still will attenuate, just not as much. Lots of pop rivets ....

Bob

On Mar 13, 2010, at 8:10 PM, jmfranke wrote:

> For detailed measurements of six different choke ring GPS antennas, see;
> 
> http://facility.unavco.org/project_support/permanent/equipment/antennas/ant_cals.html
> 
> 
> John  WA4WDL
> 
> --------------------------------------------------
> From: "WarrenS" <warrensjmail-one at yahoo.com>
> Sent: Saturday, March 13, 2010 7:46 PM
> To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
> Subject: Re: [time-nuts] Choke Ring Design for L1
> 
>> 
>> 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
>> 
>> 
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>