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.
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