The most UNDERESTIMATED antenna out there is the ____________________________________

[K2NCC]

I agree with N5YPJ. My 3-foot horizontal mag-loop.

[W3RXO]

I would have to say, that for me, a good, basic antenna, is a resonant length, mono-band dipole, either wire, or tubing, in whatever configuration, you choose. Inverted V, maypole, flat top, V, L, single feed point fan-type multiple resonant length dipoles, all seem to be the best basic antenna.
But, as for my favorite, as I have not yet settled on ONE band I wish to hang out on, I like an M2, 7&10-30LP8-125, log periodic, or a four element, multiple band quad. Of those two, I prefer the performance of the quad, but they are tedious to tune, or expensive to buy, pre-tuned, difficult, at best, to erect, and harsh winters can wreak havoc on the wire elements. So, like all antennas, the alternative is a "compromise" antenna, and that would be the log periodic. Gain, on all bands it covers. Back door, and side, rejection, and generally good SWR, across the portion of the spectrum it covers.

Now, that I have opined about my views on antennas, in general, to answer the question, of what I think is the most underestimated antenna, I would have to hand that to the maypole. I'd bet that half of the hams out there don't even know how to build one shabbily, leave alone doing one well. Cheap to make well, and a top notch performer, in my opinion. It will be the first antenna, to be erected at my new home. Then, up go the towers, and the log periodic will likely be my choice, unless I get ambitious, and decide to go with a Cubex Mantis II, 40+4L5B

Due to the difficulty to erect correctly, I might also nominate the quad as an underestimated antenna. I was told by an Elmer, at an early age, that the first, and last signal, which you will hear in propagation, will be using a quad.

[K2MMO]

Homebrew dipole

[N7WR]

I think it's the multi-loop, stacked, 64-rhombic array.

Hardly hear anyone using one, but when you do, they're really strong.

They developed AM's place on the PV Pennensula many years ago---but being a young ham growing up in LA I had the opportunity to see his rhombic farm many times

[WA4BRL]

2-element Yagi

[LZ2ILR]

the small magnetic loop: it drops noisefloor by up to 3 s points, can tune at least 4 bands reasonably, and can work below shoulder height. also it has those sharp nulls that totally knock out local qrm.
i have one that cost nothing to build out of old water pipe from a dumping ground. its best score was sitting on my living room table in bulgaria getting a 2 way 59 to washington dc on 1 watt.
you can see it here:

http://www.youtube.com/watch?v=shM_WH8epEs&feature=plcp

[KG6MZS]

I'm going to go with the rotatable dipole as well. I've made them for 15m and 10m and they play really well for such an easy and inexpensive antenna.

[N8HM]

Another vote for magnetic loops. 138 DXCCs from my apartment in DC since early last year with them. 106 of those were worked QRP.

[WA7PRC]

2-element Yagi

I have one of those, a Force12 C-4XL. It's 2 elements on 40m, 2 elements on 20m, 2 elements on 15m, and 3 elements on 10m at 72' AGL:



40m is linear loaded. 20-15-10m has no traps or loading coils. It regularly busts pileups on the first try, with "you're VERY loud" reports (even with only 100W). Wotta flamethrower! The Crushcraft AR10 half wavelength vertical on top is at 83' AGL and works a BUNCH better than when it was at 20' AGL. The 80m cage inverted vee is at 70' and the 40m single wire dipole is at 65'. They work well, too. A 20m half wavelength vertical on the roof may get changed to a 40/20m design, thanks to K6MHE.

[WW7F]

I just happened to find an ISOTRPIC antenna for sale online, really great deal too,just LOOK! http://www.testequipmentdepot.com/ka...3371?ref=gbase
And for the paltry sum for the antenna you too can own a 20 mhz to 1 ghz isotropic radiator with a whopping 1 watt power rating! BTW, I am interested in trying a magnetic loop here if for no other reason than to have something to get me on the air with one to test it out and see how well I can do with it, not going to use nmore than 100 watts max anyhow.
But for the asking price of only $3,298 you too can own an isotropic antenna 73 Michelle