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I need some advice on setting up my first HF station in a somewhat restricted townhouse community. If I had a detached house with a backyard I’d probably already have everything setup. But with this townhouse I keep second guessing what to do.

Townhouse Specs:

  • Freehold (I can attach things to the outside. But wish to remain discreet.)
  • 4 story
  • No back yard
  • Deck is located above the car garage
  • There is a small balcony outside the 4th floor master bedroom
  • No attic
  • No basement

Known:

  • Radio: ICOM IC-7300
  • Power Supply: Astron RS-35M

Need help:

  • Antenna
  • Grounding (no place to install ground rod(s))

The magnetic loop keeps coming up in my research for situations like this. And I have also read some of the SGC documentation for their Smart Tuners. If I understand correctly I could using a SG-237 and do the following without the need for a earth or counterpoise. Based on any of these I should be able to do some variation with my outdoor space (deck and balcony),

Do you think going with a magnetic loop like those from MFJ is a better option that doing one of the many wire antenna options with a SG-237? People seem to like MFJ magnetic loops other than some quality control issues and learning to turn it. The reviews of the SG-237 are also positive.

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  • $\begingroup$ Which bands are you the most interested in using? $\endgroup$ – Mike Waters May 26 '17 at 12:27
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    $\begingroup$ I once used an SGC auto-tuner for a single wire (arbitrary length) antenna plus counterpoise wire (just laying on the ground) and it is not a bad antenna. In fact, I currently use a variant of the same approach using my portable ops wire antenna from K7BHB called the Versa-Tenna. It is a much cheaper solution (you don't need the SGC tuner), about $80. Google Versa-Tenna and find the eHam.net reviews and read them. $\endgroup$ – K7PEH May 26 '17 at 14:37
  • $\begingroup$ @MikeWaters My knowledge of the bands is limited to what I've read about them and what each offers. Based on that I'd say 40m to 10m. $\endgroup$ – ifletch May 26 '17 at 16:35
  • $\begingroup$ @K7PEH thanks for the info. I will check the Versa-Tenna out. $\endgroup$ – ifletch May 26 '17 at 16:37
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    $\begingroup$ @K7PEH Please don't use comments to write answers, even partial ones. $\endgroup$ – Kevin Reid AG6YO May 26 '17 at 16:43
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The design of antenna called a magnetic loop has the disadvantage that it has a very narrow bandwidth, and the frequency is set by a variable capacitor mounted on the antenna. This means that changing frequencies requires you to go to the antenna and turn a knob. If your operating position is not next to the loop, this is very inconvenient.

The loops in the Smartuner document you link are not that antenna design (there is no inner loop). But they do have a similar property of placing a tuning element at the feed point of the loop — just this one is automatically controlled, which will be much more convenient, but more expensive.

However, as non-resonant antenna systems go, a tuner at the feed point is the best possible configuration for minimizing loss. If you think you can fit it in your space, that would be an excellent choice.

In any case, you do not need a RF ground for any kind of loop antenna to function properly. If you look at the instructions, the “ground” terminal of the tuner is in fact to be connected to the other half of the antenna — it's just that in vertical/“end-fed” designs the ground is the other half, but in any loop it's the other end of the loop wire.

Depending on whether the tuner incorporates a proper balun (I can't tell) you may want to add a choke at the input to the tuner. This prevents the feed line from becoming unintentionally part of the antenna and radiating your transmit power (all the way back to your operating position and causing interference, computer crashes, or shocks in the worst case).

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  • $\begingroup$ Thanks Kevin. You have helped confirms things I have determined while researching. I use stackoverflow all the time at work and figured this would be a good place to come to find some help. I will look into whether the tuner incorporates a proper balun. If I do need to add a choke can you suggest what I should be getting. $\endgroup$ – ifletch May 26 '17 at 16:30
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    $\begingroup$ @ifletch That's a fairly separate question, and I don't have any expertise there to write a comprehensive answer. I recommend posting it as a new question (and don't forget to frame it as "what characteristics should I look for, or make it with" not "recommend me a product"). $\endgroup$ – Kevin Reid AG6YO May 26 '17 at 20:16
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If you are close to the down spout or rain gutter why don't you try loading that up but you will almost certainly need an tuner in the transmission line. You would just feed like a single wire feet line. Other things you may need to do is use an UNUN at the transmitter antenna in put and the ground may need to be tuned with a series resonant circuit sometimes called an "Artificial Ground". I lived in an apartment before I got married some 40+ years ago and worked an awful lot of stations and today you have all kinds of sound card digital modes are available to you making the task much easier and more reliable. Hope this helps you in some small way.

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A magnetic loop can work well if it has two qualities: enough power handling (a 5 kV vacuum variable will handle the 7300's 100 Watts); and a decent remote tuning setup. Tuning is critical, as eHam reviews show the main difficulty is getting the SWR properly dipped. Thanks to the popularity of robotics, low cost stepper motors are available, and do the job.

While size isn't critical, efficiency goes rapidly downhill at diameters less than than about a 20th of a wavelength. 1/2" or 3/4" copper tubing is self supporting, low loss, and is easily flattened and drilled for low loss connections. Paint it a dark color for stealth, and to avoid corrosion.

Dealing with high voltages and extreme narrow bandwidth are the price paid for an antenna that makes a magnetic near field, which seems to penetrate nearby conductors, such as trees, the ground, house wiring, powerlines, etc. almost as if they weren't there, because induced currents are in phase with the antenna's field. Near field losses are reduced by an S unit in a typical urban location, when compared with a wire antenna or a vertical whose electrical near field induces out of phase re-radiation.

Stealth is achieved not only by small size, but also by suppression of RFI which does not emanate from the loop's matched feedline, since tuning and matching is done at the antenna.

Further details are at http://www.x44.cc, or by Googling my ham callsign, K1QAR

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  • $\begingroup$ The third quality is loss. More loss = Less power handling ability, and vice versa. (What does that tell you about the MFJ loop? ;-). See w0btu.com/magnetic_loops.html. $\endgroup$ – Mike Waters Jun 11 at 20:03
  • $\begingroup$ Ted, welcome to hamSE! I have reopened your question. We look forward to seeing more of you here. :-) $\endgroup$ – Mike Waters Jun 12 at 2:09

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