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For a typical EFHW antenna, let's say we are in a very space-restricted environment, says a hotel room. I am thinking of the idea loop around the wire around the room, maybe even many loops.

This is just an "get on the air somehow" antenna, and I know it would be very compromised.

What I am curious is how this will likely change SWR curve and pattern? Would the turns add the inductance?

Sorry if I make it confusing EFHW and Long Wire, I don't really understand the detailed difference.

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    $\begingroup$ when you say "loop", how do you plan on connecting your wires, exactly (either way, it's not going to be a EFHW or long wire after looping). $\endgroup$ – Marcus Müller Sep 22 at 11:31
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    $\begingroup$ Welcome the hamSE, Matthew. In order to give you any meaningful help, we need to know more about the actual wire configuration you propose. Otherwise, there are simply too many variables to consider. $\endgroup$ – Brian K1LI Sep 22 at 12:26
  • $\begingroup$ Is there a reason why you chose an EFHW and not a balanced antenna like a dipole? $\endgroup$ – Mike Waters Sep 23 at 18:33
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I had an antenna like this in an apartment many years ago. I was able to get out somewhat. Most likely the higher up you are in your complex, the better. But it took a kW amp and a matchbox to generally let my signal be heard. It was a fun project and did keep me on the air. Not well but on the air none the less. If I were to do it again I think I would try for a drop down wire out the window, retrievable after the session was over with and probably best at night time under the cover of darkness.

As an aside I had a couple of visitors who also resided in the complex over and their eyes caught the wire strung all around at the ceiling level and they had questions. I explained that it was for my stereo (never mind that there was no connection of the wire to the stereo. And that it allowed me to receive a desired distant station that I could not hear without it). They accepted the answer as very reasonable and forgot about it.

A plus for the setup was that one of my neighbors liked to leave the bars at closing time and bring the party back to his unit accompanied by full on volume of music rattling the walls. Not wanting any involvement by the super for obvious reasons of my own stealth operations I proceeded to crank up the kW on 10 meters and sure enough his stereo was a fine one for picking up the stray RF, the buzz's and whistles that out of tune and near proximity from a tx can produce. It was even more hilarious when I took to the morse code key allowing many thumps to be added to the music beat. The stereo would be shut off and re fired up over and over a few times to 'fix' it and failing that all of a sudden car doors could be heard opening and slamming shut, signaling that the party was moving to a more hospitable location and one with a 'working' stereo. True Story both.

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"EFHW" means end-fed half-wave. It is by definition a half-wavelength long, so it is not short. And it's fed at the end, so it can't be a loop, which has no ends. I wouldn't say it's a very good choice for a space-limited application.

There are loop antennas too, and any wire antenna can be bent or curved, though that may make it a very different antenna. Any wire will radiate, but the radiation pattern and feedpoint impedance may be substantially altered. That doesn't mean it won't work, it just means someone would need to build the antenna and measure it to find out, or enter the precise geometry into a modeling program.

However, in your situation, I would recommend looking at antennas designed for mobile use, rather than trying to cram a large antenna in a small space. Going this way I think you'll get more consistent performance.

For example, see the MFJ Ham Stick. Ideally you can mount it on a balcony railing similar, but if such a thing isn't available you can lay out some radials made of ordinary copper wire. There are also brackets that mount two of these antennas base-to-base, making a short dipole which requires no radials.

Of course there are many such antennas, and some are tunable, can operate on multiple bands, and so on. The Ham Stick isn't anything magic, it's a monopole antenna with some inductive loading. You can make your own such antenna by winding a coil and sticking it in the middle of a stiff wire. And if you enjoy antenna experimentation I absolutely encourage you to try it, but if you just want to get on the air you can find mobile antennas that are really cheap and don't need anything but minor tuning adjustments to get on the air.

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I've beed working in "very space-restricted environment". From what I know there are two options:

  1. Shortened vertical, like OPEK HVT-400B and similar. Can be home made as well. Such vertical will work OK on 10m-40m from a balcony, assuming there is space for 5m+ radials.
  2. Magnetic loop antenna. Doesn't require radials but it's very narrowband and typically can accept only 10-40W unless a vacuum capacitor is used. Still it works quite well for CW and FT8.

If you have a window and a tree nearby I highly recommend long wire antenna. A peace of 23m wire + 7m counterpoise + antenna tuner will bring you on all HF bands with good performance. Another option is Fuchs antenna. It doesn't require a long counterpoise, but will bring you to 40-10 meters with the same matching unit.

From my experience the main challenge of working in such environments is not antenna performance, but the noise from switching power supplies though.

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