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I was reading up on the different amplified loop antennas, like the W6LVP or the MLA-30.

Most reviews say "great reception", or show a SDR waterfall with a lot of stations, or show a random station coming in really strong. They also talk about how good they are for "serious SWL". But in most cases they don't show a 2-way QSO with a DX station. And SWL isn't really that relevant since the remote commercial station may be pushing 250KW anyways.

Are those antennas any good for amateur radio DX operation?

I'm in South America. So basically all I do is DX: 8000km is usually the minimum kind of distances I operate to (there are few stations in SA except for Brazil, who are at least 1500km from me anyways).

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In short, yes. Receive antennas can do lots of good things for hams. They're most popular on the "low bands" (80 meters and longer), but can be built and used for any band. They're not magical, but they do offer chances to null out local noise sources if carefully placed and adjusted. Some hams go to the length of installing 4 or more receive antennas with phasing combiners so that they can electronically "steer" their pattern to maximize SNR for the station they want to hear. This can be expensive, but it's cheaper than doing the same thing for transmit because the power levels involved are much lower.

A single active loop won't let you do that, but:

  1. It's a decent receive antenna with a stable pattern for several bands.
  2. Since it's physically small, and pre-amplified, you can place it on whatever part of your lot has the least near-field RFI (useful if interference is coming from your own house/shack, or one noisy neighbor).
  3. It has two nulls that you can point towards offending noise sources.
  4. It has a good (almost hemispherical) elevation pattern, with very little sensitivity to height above ground, so it's as good for DX as NVIS.

One caution with any kind of pre-amplified antenna; if you live within a few km of a strong (10kW or more) broadcast station, you may have a very hard time preventing overload of the preamp. I know from experience — I have three different 50kW stations "in my back yard".

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  • $\begingroup$ What about city noise? I don't think it comes from any particular direction. $\endgroup$
    – hjf
    Jun 17 '20 at 19:24
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    $\begingroup$ @hjf there's no magic to make noise that comes from all directions just go away. All you can do is try to null out the strongest sources. $\endgroup$ Jun 17 '20 at 20:50
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    $\begingroup$ @hjf there's some sort-of-true things about that (for example it's not true that magloops "only respond to the magnetic component", but it is true that an antenna's impedance is different in the near field and the far field, and different antenna designs vary in different ways, so a loop might be relatively deaf to an interferer within ~1 wavelength), but only about 10% of it is true, and more importantly I don't know of any way to take advantage of most of those properties other than trying something and hoping to get lucky. $\endgroup$ Jun 17 '20 at 23:28
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    $\begingroup$ @hjf by contrast, making antennas that maximize the ratio of (gain in the direction of the signal you want to hear) / (gain in the direction of your worst noise sources) is tried and tested and not pseudoscience. $\endgroup$ Jun 17 '20 at 23:30
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    $\begingroup$ @hjf maybe. A loop doesn't have very high gain in any direction, what it has is two sharp nulls in opposite directions. So you don't point the peak at your target, you point one of the nulls at the worst noise source you have, and hope that lowers the noise floor enough to let you get the signal. $\endgroup$ Jun 17 '20 at 23:38
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What's the background RF noise level at your antenna's locations for your bands of interest? In environments with high levels of broadband background RF noise (neighborhood or computer EMI, etc.), a receive-only loop can help reduce the RF noise pickup, especially if the noise is directional and/or polarized the same as your non-loop antenna(s), and thus improve the S/N of weak DX signals. But in quiet RF environments, the advantage is far less.

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  • $\begingroup$ S7 in a good day. S8-S9 most of the time. I live in the city so noise comes pretty much from all around. $\endgroup$
    – hjf
    Jun 16 '20 at 16:46

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