[time-nuts] antennas was Re: Common-View GPS Network

[Jim Lux]

On 4/17/13 12:18 PM, Chris Albertson wrote:
> Another way to ask this question is "what is the effect of a small
> deviation form the ideal dimensions?"
>
> If we assume deviations of about 1/20th of a wavelength are OK then we can
> allow about 1cm of dimensional error.  Almost anyone using simple hand
> tools can do better.
>
> With care using primitive "garage" equipment we can do much better.  The
> old-school hand method for precision sheet metal work was to make a
> hardwood form and then bend and cut the metal around the wood form.
>
> I think if a cake pan would work is a matter of luck.  You'd just have to
> find one within about 2cm of the correct diameter.  If not then you be
> better off starting with flat sheet and hand shears.
>

since you can buy cake pans in even inch increments, I think the cake 
pan will work..

BTW, I've been looking at some choke rings with only 2 rings instead of 
the usual 3.  Apparently, the performance isn't all that much different. 
  When I asked why do all the other ones have 3, it boils down to "the 
first one had 3 and everyone just copied it".


Javad has a bunch of choke ring theory..
http://www.javad.com/jns/index.html?/jns/technology/Single-Depth%20Low-Multipath%20Choke%20Ring.html
http://www.javad.com/jns/index.html?/jns/technology/Choke%20Ring%20Theory.html

Their conclusion is you want the depth of the ring to be slightly more 
than 1/4 lambda.  lambda/4 for L1 is 1.87" so a 2" cake pan is just 
about the right size.