Magnetic Loop antenna for HF - HomeBrew Forum at eHam.net

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eHam.net Forum : HomeBrew : Magnetic Loop antenna for HF

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Magnetic Loop antenna for HF	Reply
by 2E0BSS on February 3, 2008	Mail this to a friend!
I've been reading through the forums regarding antenna styles for restrictive areas. I have one of the worst I have no garden as I live in a block or semidetached flat on the ground floor. My council are really restrictive too as they are working on CB regulations with complete avoidance of Ham users. Currently I use a half size fixed G5RV with the ends pointing downwards to fit on the buildings roof so my transmitting is limited to say the least the antenna sides are North/North East with both ends pointing to ground Would a magnetic loop be of benefit? also is there anyway to make on multi band without getting massive? I've found one for 80 and 40 thanks

RE: Magnetic Loop antenna for HF	Reply
by KD0AFK on February 4, 2008	Mail this to a friend!
Actually a magloop is by definition less than a 1/4 wave so it can be as small as you want to make it. Realistically though it performs the best when it is at 1/4 wave which means making an 80 meter loop 20 meters in circumference. 6 meters in diameter would be the size. I have seen them all different sizes. Are you running QRP or higher wattage? The advantages of a magloop is that although it doesn't perform better gain-wise than say a dipole, it has a better takeoff angle at lower elevations so you don't have to hoist it as high as a dipole. also, it is quieter because it only picks up the electromagnetic portion of the radio spectrum, effectively filtering out the noise made by car ignition systems, street light and such. I hope this helps. I am also looking in to making one of these and all of the info I gave you is from memory so please anyone, correct me if I am wrong on any points.

RE: Magnetic Loop antenna for HF	Reply
by KD0AFK on February 4, 2008	Mail this to a friend!
have you thought about a vertical dipole hidden in a flagpole?

RE: Magnetic Loop antenna for HF	Reply
by N7HTS on February 7, 2008	Mail this to a friend!
I recently built one. It is octagon shaped and about 132 centimeters in diameter. I'm using coax cable as a capacitor. So far, I've been able to tune it on 20, 30 and 17 meters using different length of coax. I am feeding it with a Faraday loop. It's very narrow banded but, it seems to work quite well. I will soon be homebrewing a butterfly capacitor for it. I have limited space in my backyard and I have vertical antennas but, they are very noisy. The reason I built one was to help lower the noise level and it does. I've compared the signal strength on receive with my verticals and sometimes it is much stronger with the loop and other times it is not as good. I have it about 45 centimeters above the ground on a PVC stand. I'm going to try to elevate even higher. I would say that it is well worth the effort to build especially if you are in an apartment. The only drawback is that it is very narrow banded.

RE: Magnetic Loop antenna for HF	Reply
by KL7AJ on February 8, 2008	Mail this to a friend!
Magnetic loops have to be built VERY robust to work effectively, since you will have massive circulating currents. You need a tuning capacitor BUILT for this...i.e. a butterfly cap, and FAT tubing. But, it's certainly worth a shot. Eric

RE: Magnetic Loop antenna for HF	Reply
by JDWYER on February 9, 2008	Mail this to a friend!
I build a magnetic loop and it was a dog. Total waste of money. Unless you have an expensive capacitor there are high losses. They are hard to tune and must be retuned every few kilohertz. They receive better than they transmit. The one I build needed about 20 watts out to make QSOs on PSK-31. I can do the same with 5 watts using a dipole or compromised vertical. John

RE: Magnetic Loop antenna for HF	Reply
by JDWYER on February 9, 2008	Mail this to a friend!
Also you are exposed to a lot of radiation if you use it indoors. Things to think about.

RE: Magnetic Loop antenna for HF	Reply
by N3OX on February 10, 2008	Mail this to a friend!
"I build a magnetic loop and it was a dog. Total waste of money. Unless you have an expensive capacitor there are high losses" You gotta do it all the way, mine actually works great for something its size but does have a $200 vacuum variable in it. If you don't have space for anything bigger it's a GREAT antenna, I think, if you spend the money for the copper tubing and good capacitor. If you do have space you should do something bigger and more tolerant of construction practices! Max Gain Systems has the best prices on vacuum variables that I've seen, by the way. I'm sporadically working on some ultra-cheap magloop ideas but it hasn't quite come to fruition. For a fixed frequency one I think using a single piece of aluminum flashing to make the loop and a parallel plate capacitor has some promise, but it's not easy to retune. That's what I'm working on, but not very hard. ;-) http://www.n3ox.net/projects/magloop/magloop1_lg.jpg is a picture of my copper + vac. variable magloop 73, Dan

RE: Magnetic Loop antenna for HF	Reply
by KB7NRK on February 12, 2008	Mail this to a friend!
In the early '90s '73 Magazine had an article for an indoor loop antenna for QRP. It looked like a vintage spiral antenna loop. The guy hung it from the ceiling. It was very simple, just the loop, a variable cap and lead with alligator clip to short the loop for different bands. A compromise?... You bet but it did work. I only wish I could remember the month and year.. I thinkit was 1991. John KB7NRN

RE: Magnetic Loop antenna for HF	Reply
by KL7AJ on February 25, 2008	Mail this to a friend!
Dan: Same deal with the DDRR. If you look at the ORIGINAL plans, it uses muffler pipe for the ring...and if you DO that, the antenna actually sort of works...kind of....a little bit. A DDRR made of WIRE is worse than a dummy load, though. At least on 160 meters...HI.. eric

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