[Elecraft] Experiences using a portable HF loop

Sat Apr 22 14:19:47 EDT 2017

The electric field of a horizontally polarized antenna is parallel to 
the earth and it induces significant current into lossy earth if 
its less than about 0.1 wavelength high (14 feet on 40 meters). 

If you can install a horizontally polarized antenna 0.1 wavelengths 
high or higher, its efficiency is superior to field expedient 
vertically polarized antennas such as "magnetic" loops. This 
is why end-fed half wavelength (EFHW) horizontally polarized 
antennas are so popular with QRP back packers where efficiency 
is very important. 

On a mountaintop, a relatively low EFHW antenna can produce 
astounding QRP results. These affects are very easily observed 
(and measurable) with a 200 milliwatt WSPRlite transmitter and 
a USB battery that will easily fit on your pocket. 

On the other hand, vertically polarized antennas -- such as small 
"magnetic" loops -- produce significant low angle radiation 
even at very low heights. Unfortunately they also suffer from 
proximity to lossy earth. They really excel at a salt water beach 
(but you must be very close to salt water) or in a salt marsh (not a 
particularly pleasant place to take your family or girlfriend,,,). 

73 
Frank 
W3LPL 

----- Original Message -----

From: "GRANT YOUNGMAN" <ghyoungman at gmail.com> 
To: "Elecraft" <elecraft at mailman.qth.net> 
Sent: Saturday, April 22, 2017 5:36:33 PM 
Subject: Re: [Elecraft] Experiences using a portable HF loop 

A wire will not always outperform a loop. It depends among other things on whether or not you have a way to hang the wire at a reasonable height. Typically useless on the beach, for example, unless you pack a pole or two to get it up in the air, which means guys and all the rest. Doable, of course, but a lot of junk to tote around even if you have relatively compact extendable poles, plus the time to put it up. Poles/guys can be a problem when there are a lot of people around (beach/park/etc) or children who will be attracted to them like a magnet to trip over, etc.. You get the picture. It’s these kinds of situations where the loop shines. Stick it on a table or light tripod and you’re on the air in 5 minutes. 

With my KX3, depending on where I’m going and what the landscape looks like I use one or more of various wires, Buddipole hardware (light weight mast, shock cord whip, miscellaneous bits), or an AlexLoop. I’m currently waiting delivery on a W4OP loop. The best I can say about any of these options is that if it’s what you have, use it. They all work, sometimes surprisingly well. After a couple of years of this, I can’t say definitely which is always “best”. I”m getting too old and decrepit to still be much of a hiker, so I’m generally driving somewhere and walking a relatively short distance to a picnic table in a park, down to the neighborhood dock, or the beach, etc. 

The AlexLoop is very light to carry, but a downside is that it does NOT have any sort of tripod or table mount. You’re on your own jury rigging something out of PVC and clamps to hold it up, or conjuring something that can screw into a tripod, etc. (there are plans on the web). None of it is rocket science, but it isn’t just a standard part you can purchase. 

> Greetings all, I'm curious to hear from anyone using a portable HF magnetic loop. I've read the theory behind them so I'd like to hear your opinion about them? How efficient these antennas are, especially running qRP. 
> 
> 

Grant NQ5T 
K3 #2091, KX3 #8342 

______________________________________________________________ 
Elecraft mailing list 
Home: http://mailman.qth.net/mailman/listinfo/elecraft 
Help: http://mailman.qth.net/mmfaq.htm 
Post: mailto:Elecraft at mailman.qth.net 

This list hosted by: http://www.qsl.net 
Please help support this email list: http://www.qsl.net/donate.html 
Message delivered to donovanf at starpower.net 