[Lowfer] Active whip antennas

[JJ]

I did something similar.  I took about 75 feet of wire and made a sloper 
out of it.  The top of the wire was about 35' up with a rope on that 
end.  I secured the rope and then ran the bottom of the wire out to 
about 3' off the ground.  I fed the wire at the bottom through a 9:1 
balun that I had made years a go for a K9AY.  The toroid had been 
salvaged from an old computer PSU.  Instead of grounding the wire, I ran 
another 75' wire on the ground.  The other end of the balun was 
connected to 75 ohm coax.

A few weeks a go I wanted to see what a big loop would do.  I added wire 
to the sloper main wire and made a sort of delta loop.  I just kept 
splicing in wire to fill the area I had.  The bottom is about 75' I 
guess.  I didn't measure anything.  It's fed in the center of the bottom 
wire with the same balun and coax.  This loop is oriented E-W and I've 
added a smaller loop that's N-S.
These loops out perform the old sloper by far.  I've logged NDBs in 
North Africa, Sweden, Poland, Brazil, Chile and more with these loops.
I just ordered the parts for a Burhan Loop, the next experiment.

Jon W1JHJ

On 12/19/2010 8:59 PM, Bill Ashlock wrote:
> This leads me onto my 'tree antenna' soap box. I seldom use E-probes because of their IM  problems... even the good ones. Instead I shoot a line over the top of the tallest tree and pull up a 30 to 50ft wire. This connects to a 50 to 5 turn transformer (77 ferrite core) at the base of the tree that has the other end of this winding connected to a ground stake. A 75 ohm coax connects to the 5 turn winding and runs from there to the shack (shield isolated from gnd). This is form of 'long wire' antenna but it's the trees conductivity that has the most effect over performance. The ground at the base of the tree also has a large effect on performance since it is located where the signal is received, not inside the typically noisy shack. The typical sensitivity of this antenna at 185K is -8db...... which is plenty for most good communications receivers like the R-75.
>
> Bill
>