[Elecraft] Magnetic Loop Antenna Question

[Fred Jensen]

Try muffler repair shops.  I think most new ones get the pipe pre-formed 
from the suppliers, but an older one might have the equipment to do it. 
Or, make it octagonal with soldered fittings, there really is no 
discernible difference.

An 18 ft circumference loop with 1" copper pipe will be about 50% 
efficient on 40, with a BW of ~5-6 KHz [Q is about 1,000].  That's close 
to as small as you'd want for 40, just outside the upper limit for 20 
and it will transition to an E-field antenna above 14 MHz, basically it 
becomes "an elevated conductor."  About 5KV across the capacitor @ 100 
W, resonant current will be a bit north of 20 A.

The RF loss-resistance of the pipe will be higher than the DC resistance 
since the RF sees only the outside surface of the pipe.  I'd look into 
some way of getting that cap to the bottom of the loop.  On a 5 ft 
tripod, the top will be close to 11 ft in the air with a big 
"falling-over moment" in the wind.

73,

Fred K6DGW
- Sparks NV DM09dn

- Northern California Contest Club
- CU in the Cal QSO Party 7-8 Oct 2017
- www.cqp.org

On 11/12/2016 1:36 PM, rick jones via Elecraft wrote:

> Anyway I'm
> having a hard time finding someone to bend the copper pipe. It takes
> a rolling tube bender and I don't want to invest $150 at Harbor
> Freight to use it a few times! Most local garages can't bend 1" pipe.
> Too small. I need to find a fabrication shop. I could use soft copper
> and try to make a good circle but I'm a little too OCD for that!