On Sun, 05 Jun 2005 16:57:03 GMT, GeorgeF
wrote:

I put up an 80 meter full wave loop using about 280’ of #14 wire in
almost a square. Each end of the loop was soldered to an SO-239
connector. I’m feeding the loop via RG-8 coax, about a 30’ run.

I have a 400 foot loop that is more triangular than square but it
still seems to work pretty well. The biggest difference between our
antennas is how they are fed. I use 450 ohm ladder-line to a balanced
tuner (Johnson Matchbox) to my FT-897D. According the Yaesu's display
a suitable match can be obtained on all bands except 30 and 60 meters.

I can also use the antenna on six meters with a homebrew matchbox for
that band. A two meter matchbox is in the works.

Using an MFJ Antenna Analyzer I can’t find a nice low SWR point. The
lowest I can find is at 2.5 MHz, the SWR at that point is still high at
3.4:1. In the 80 mtr band its 8:1 and in the 40 mtr band its 7:1.

The impedance, is that the right word?, of a loop can be several
hundred to several thousand ohms. As you have found, the antenna is
not a fifty ohm load.

My installation is far from ideal. First, the antenna for about ½ the
loop is at about 20’ high and the second half is about 15’ high. Next,
in the center of the loop is the metal frame work for a screen-room over
the swimming pool (50’ x 30’) which I’m sure interacts with the loop
antenna to some degree. The screening is not metal however the frame
work is.
The antenna is what it is. Although a little more elevation would be
FB I wouldn't be too concerned with what is in the middle of the loop.


Of course I can use my MFJ-949 tuner to get a low SWR on any band but by
doing so am I loosing efficiency? I also notice that trying to tune the
loop the tuner seems to be very touchy! I have noticed on 20 meters
the loop received on average about 2 S-Units better than my 20 meter
dipole. On 40 meters it receives almost 1 S-unit better than a 160’
randomwire. On 80 meters just slightly better than a 160’ randomwire.
(all antennas I’m comparing are all at about 20’ high).

I would have started making the loop shorter to bring up the resonate
frequency to 80 meters however I’m concerned as to why the lowest SWR I
can find anywhere on the HF band is still over 3:1. Is it because the
loop low to the ground (20’)? Or do I need a balum? 1:1 balum? 4:1
balum? Looking for any suggestions.

Ack, do not shrink the loop!!!!! The tuner you have can be used with
a balanced feeder, the built-in balun should be satisfactory. Try
feeding your loop with 450 ohm ladder-line from the tuner and things
should improve significantly.

73 de n4jvp
Fritz