The AM Forum

Radio talk show host Art Bell's giant double loop antenna at his Nevada QTH is well known out here in the West. It is a large double loop of wire strung out amongst several acres supported 75 feet in the air on 13 poles. The circumference of wire is 1595 feet, and since there are 2 loops, that's 3190 feet of wire. (I've heard this setup on 75 meter SSB, his sig is strapping into LA) God help us if he ever takes an interest in AM. It's amazing what you can do when you're a millionaire ham :)

http://free.prohosting.com/ae7op/index.html

(http://free.prohosting.com/ae7op/images/aerial5.jpg)

I talked to Art several years ago on 40 meters. He was using the same antenna. He was loud. But I think it had little to do with his antenna.

I like his log periodic and other rotary stuff - that was done right.

But, take a look at the horizontal pattern of his 1595' loop on 3.8mhz:

http://free.prohosting.com/ae7op/loop1.htm

It's really a four sided quasi-cloverleaf pattern - and a distorted one at that.  Not much gain in any direction to speak of for the BIG effort.  On 40M I'd expect it to be even more of an octopus.

This could be done cleaner [and much easier] with a simple 520' centerfed dipole on 75M.  But why bother with such a crazy pattern? A guy with his money could put up a rotary 75M Yagi, or even four fixed in different directions for the effort he put in erecting (13) 75' poles and associated hardware.  If he wants omni coverage, a turnstile would be FB.

This is a case where it sounds like an impressive array, but putting that much wire in the air and not phasing it into a particular pattern is quite baffling.  

But, the 1595' long loops are probably for "wow" conversation effect.  An extradinary big signal coming outa that loop [compared to a simple dipole] can be done only one way as you said, Steve...  :lol:  Rock and roll.

T

Yes, scuttlebutt is he has a HENRY or commercial ALPHA amplifier in line at all times. But I once heard him A/B between the loop and a fullsize inverted vee up 80 feet. The loop was many s-units stronger. Maybe I'm in line with one of the loop's crazy cloverleaf lobes?

Check out his FB DX-40 station.

(http://free.prohosting.com/ae7op/images/shack11.jpg)

Hmmmm...

Those poor pattern polar plots are his OWN computer generated work, backed up by what appears to be field strength readings he took around the property as shown.

If you over laid his reference inv V on this plot you would see close to the same "gain", in the dipole's broadside direction, [within 2db or so] and assuming you were not in one of the loop's big nulls.

Another possibility is that I've heard some guys who do antenna A/B tests
who were really doing linear in/out tests... if you get my drift....

If it were mine, I'd rip that mess down in a heartbeat and replace it with a truly directional/switchable wire array that those thirteen beautiful poles deserve.   :lol:

T

I'm don't have a calculator at hand but I would think that something along the lines of a rhombic might be a better use of the supports and wire. Had I the property, I would have a 160M rhombic instead of the loop.

I talked to Art and he says it's resonant at 600 kilohertz!

Powell W4OPW

I am also envious of the antennas at Ft. Bragg  :D

http://www.custommetalworks.com/photo_gallery/ft_bragg/ft_bragg.htm

Yep, that log periodic triple stack at Ft Bragg is quite nice.  
I know the guy who designed and helped install it - Jay at
Array Solutions. I use his StackMatch torroidal phasing
system for my 6M stack.

BTW, pictured below is the "conservative" JJ homebrew log
periodic stack over here.  I sometimes wonder if I shuda did
a Ft Bragg type triple sometimes...

T

K1JJ Logs, 100'/60' high - Top Log: 12-33mhz, 60' boom,
400 pounds.  Bottom Log: 12-18Mhz, same as above but
1/2 completed.
(http://home.comcast.net/~k1jj/wsb/media/254120/site1065.jpg)