On 10/21/2015 4:42 AM, Brian Howie wrote:
In message , rickman writes

The capacitance of the loop to the screen meant that at the minimum
variable C setting ,I couldn't get the maximum frequency of about
500KHz I wanted, so I had to take turns off. I now need more parallel C
to tune the look down to 136KHz.

Wow, that loop must have a *lot* of capacitance. Is there a way to
space the conductors away from the copper tubing in the run?

Not easy

I'm curious why you would use copper pipe for the shield. Because it
provides both shield and support? I guess there are a million ways to
build a shielded loop. I like the idea of using coax, but I don't
know if that also has serious limitations from the capacitance between
loop conductor and shield.


It seemed a good idea at the time. The original design used plastic pipe
covered with tin-foil ,but I wanted something that would survive a
Scottish winter outdoors.

PVC 4-7 Loop Antenna Al Burzynski KA5JGV ( it's on the NDB yahoo group)

it used 12 turns. I think the use of plastic pipe and external tinfoil
reduces the C.

My loop does work quite well, and has survived outdoors but I think it
could be improved

Yes, well, they can *all* be improved. I find it interesting to make
stuff like this from discarded materials like rain gutter. I'm trying
to understand why one poster in a yahoo group says thin stock is no good
for transmitting loop antennas. The skin effect limits the signal to
the outer few mils of copper or aluminum. I think thin stock will do
just fine if the circumference is large, overcoming the limitations of
the skin effect. At least you are using all the material rather than
just the outer few mils.

--

Rick