Quote History Quoted:
A member here gave me TWO of the MFJ's of which I gave one away to a new ham and the other is in my shed waiting to be put up. After the last round of big storms taking all my antennas down, it will be going up in a week or so after the roof is replaced.
He told me the loop works pretty well, but is very narrow banded which is typical of small loops and somewhat directional. I'll be installing this one on a roof tripod with a rotator.
VK3YE on You Tube uses a small loop alot.
I'll post a thread on it when I get it installed.
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Hmm, I wonder who that might have been
Mag loops are very interesting antennas, and if you're space limited are a pretty good solution.
I'm going to get the one big negative out of the way first: because of how they work, you take a
pretty big hit on TX. Mag loops break the "antenna reciprocity" rule, e.g. normally antennas receive and
transmit the same. With mag loops, though, due to the high Q there are truly huge currents and the
I^2R losses in real-world construction results in about an 8dB loss on transmit. So that works out to
about 15W radiated for 100W input.
Now let's talk about all the good stuff. They're super narrowband, so while they are touchy to tune,
the good ones tune just fine (MFJ being one of the good ones in this respect), and this makes them
like incredibly good preselectors. Stations that are a few KHz away literally have no impact on the
front end of your rig, so it runs full out and is very sensitive.
They're also very quiet. You're killing a lot of the noise, and they don't respond to localized RF noise
(like power lines) nearly as much as conventional antennas.
They're pretty small, the MFJ 40M-17M antenna KB7DX is describing is roughly the size of a box fan
or hula hoop. And that "tiny" antenna gives basically the same full receive performance as a
full-size dipole.
When I did testing against my full 43' vertical with a remote tuner, the MFJ loop was on average 2dB
weaker -- but that was mounted 18
inches off the ground. I don't doubt it'd probably signficantly
outperfom a 43' vertical if the loop was installed 43' up.
With all that said, my advice to people that aren't constrained by space is to spend the same money
on a vertical and remote tuner -- it's more versatile. But if you're space constrained or have noise
issues, a mag loop is a great antenna. There's a reason that in spite of the TX losses they're popular
for QRP work (alex loop) because they're so portable, and even being 8dB down, are very efficient for
a space-constrained portable antenna.