On Fri, 12 May 2006 21:27:35 -0700, Richard Clark
wrote:

On Fri, 12 May 2006 23:26:10 GMT, Dave Oldridge
wrote:

I did some modelling and the difference between 1/2 inch and 2 inch pipe
is really only 6db and I can get nice flexible 1/2 inch pipe.

Hi Dave,

Only 6dB, hmmm? Considering the following:

I'm thinking more on the lines of switching capacitors in and out.

the switch contact resistance will probably swamp out any perceived
efficiency gain achieved by added pipe diameter. You may be lucky and
have them fuse themselves closed - luck could run the other way and
they fuse open.

Even if they don't fuse (gee Richard, its only ~100A RMS loop current
at 10W EIRP (assuming Rr of about 0.001 ohms)... but it will be hard
to achieve such high EIRP), it is some more loss resistance to drive
efficiency even lower.

I wondered about the effectiveness of the switching arrangement given
the very narrow bandwidth of the antenna, it might take a hundred
discrete tuning combinations to effectively cover the 80m / 75m band.

Owen
--

"Lee" wrote in message
o.uk...
Is there any optimum height for a 3ft dia magloop, or is it
dependent on
frequency??.

I have mine planted in the lawn with the top about 6ft from the
ground (on a
rotator!)
and was curious whether to work it against ground or put it at the
top of
the tower,
or have i completely lost the plot???, Heh heh........

Surprising how cheaply a magloop can be built for and after 12
months it
still works well!!.

Thanks.....

Lee.......G6ZSG.....

=========================================
Lee,

There is no optimum height for a magloop.

Loss induced in the ground reduces as height above ground increases.

When the height of the bottom of the loop is more than the loop
diameter, loss in the ground can be considered negligible.

This is modelled in program MAGLOOP4 which can be downloaded from the
website below and run immediately.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........