View Single Post
  #5   Report Post  
Old October 25th 07, 06:28 PM posted to rec.radio.amateur.antenna
art art is offline
external usenet poster
 
First recorded activity by RadioBanter: Sep 2006
Posts: 1,188
Default Slow wave antenna design for top band

On 25 Oct, 09:38, Cecil Moore wrote:
art wrote:
At first I was considering the actual wire length
in the braiding b ut that influence became little
compared to the current pertabutations.


Sounds like you are working on a self-resonant coil
and need to know the length of time for the current
to flow from end to end.

Both sides of the argument are wrong on that one.
The current does not jump from one end of a coil to
the other in a very small number of nanoseconds as
one "expert" has asserted which implies a VF close
to 1.0. Neither does the current follow the wires
directly round and round the coil as asserted by the
other side which would imply a VF around 0.01.

The actual measurable VF of a coil seems to be just
about double the round-and-round argument side as
there is indeed some coupling between adjacent coils.
A typical 75m Texas Bugcatcher 6" dia, 6.5" long,
4 tpi coil has a VF of around 0.02 making it about
40 degrees long at 3.8 MHz.
--
73, Cecil http://www.w5dxp.com


No Cecil you are following a fatal aproach by using
lumped loaded circuitry which is a no no when measuring current speed.
Especially when you are following a path of zero standing waves.
To obtain a voltage doubling you can only solve by using
distributed loading aproach where a single wire has approx length
when measured close to the ground short of two wavelengths .
Unfortunately by using braid to get extra current perbutatation
the length extends quite a bit longer even tho braiding electrical
length is longer that the physical measurement.
Ofcourse the introduction of a flyback transformer would be
exciting but we must not run before we walk
Regards
Art