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Author Topic: Loop Antenna in 15th Floor apartment.  (Read 5490 times)
KA2ZEY
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Posts: 78




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« on: April 30, 2013, 01:47:03 PM »

Hi all,

I recently moved into a 15th floor apartment in a big city. The building itself is not immediately surrounded by any other buildings and has a decent amount of space for operating on my balcony. I use an Elecraft KX3 and Alex Loop. On the balcony, I've had good success with QRP and can hear stations from far away. I've only operated out there twice because it has been too cold. I had thought that indoor operation while not as good as the balcony would still be very good given the height but the difference is very sharp between the balcony and indoors. I can hardly hear anything indoors. I understand that the building is made of concrete and metal but even close to a window it's still dismal. I'm wondering if this because I'm using a loop antenna which does not work well near walls or objects. I'm wondering if I switched to a small vertical or long wire with antenna if I'd have better luck with indoor operation. Again, I'm surprised by the poor performance at such a good height.

Thanks,
Demian
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W5WSS
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Posts: 1783




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« Reply #1 on: April 30, 2013, 02:56:51 PM »

Assuming there are more floors above yours? Preventing access to the roof top Your height above ground lends itself to either horizontal or vertical oriented and radiating families of antennas relative to hf skywave work. A vertical dipole or sloper could work reasonably from your balcony radiating in any direction away from the building and less so through it, roughly half the compass bearing.

The loop family of self contained antennas offers utility, make it as large a perimeter as possible around the balcony opening. Use a loop tuner at the feedpoint and make it weather proof.

The balanced top fed L dipole can be a very good performer and responds well for multi band service with again a tuner at the feed point best, but in shack tuner and a short run of antenna lead coax less than 20ft is OK.

A Hustler mo-1 shaft with the resonators should fit from deck to ceiling then place at least two horizontal radials symmetrically routed and centered that travel in opposite directions from each other in the space for return currents to be radiated by the vertical portion of the system.
Use a good 1:1 current balun and again a tuner together at the antenna base and weather proof.
In all cases regardless of which antenna you choose when the tuner and balun is together at the feed point a coaxial antenna feed line can be operated in the matched state and lengths can be relaxed allowing for normal longer feed lines.
A station safety ground should be included connecting to the ac mains Do Not interconnect the ac mains ground to the radials leave them isolated and use a disconnect from the antenna for example the antenna feed line disconnected both at the antenna and the station simultaneously when away or stormy weather.

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NJ5G
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Posts: 5




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« Reply #2 on: April 30, 2013, 04:01:22 PM »

What we used to call a cat's whisker antenna would work for you.  A cat's whisker was 4 horizontally polarized dipoles shortened by making them a helically wound conductor on fiberglass poles. No counterpoise, radials, or ground needed.

A vaguely similar antenna can be constructed for multi-band operation by using pairs of Hustler resonators on two masts connected so as to be insulated from each other.  Basically a really short dipole.  Center insulator can be made from glass epoxy circuit board or...

For a mast to get the dipole up in the air a bit, consider a length of PVC pipe.  For more rigidity use EMT electrical conduit or chain link fence top rail.  The chain link top rail is available at all the big box stores like Home Depot or Lowe's in 10 ft 6 in lengths with 6 inches squeezed smaller so it can fit into another piece.  A couple pieces can be easily assembled temporarily and pulled apart for easier storage. You will need to home brew a center insulator for this dipole that also insulates it from the galvanized steel fence top rail.

This dipole is easy to rotate by hand and works well for its size. You should get as good or better performance with it as anyone mobile with a Hustler type vertical with interchangeable resonators.

There are adapters that let you use 3 resonators at a time so you get easier (instant) band changes.

Good luck and please let us know what you end up doing,

73

Patrick AF5CK
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KA2ZEY
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Posts: 78




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« Reply #3 on: April 30, 2013, 08:24:15 PM »

There are 2 more floors above me and mounting or hanging anything off of a balcony is a not permitted. I will have to figure something out for indoor use only. This is for when it's too cold to operate the loop on the balcony (which does work great). I'll experiment with the above mentioned ideas.
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K7KBN
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« Reply #4 on: April 30, 2013, 09:22:26 PM »

Concrete generally means rebar, and with the structure including metal besides the rebar, you might as well be in a Faraday Cage as far as HF is concerned.  Lotsa luck!
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73
Pat K7KBN
CWO4 USNR Ret.
WB0FDJ
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Posts: 153




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« Reply #5 on: April 30, 2013, 10:21:05 PM »

Demian

FWIW I lived in an apartment building for several years. No matter what kind of antenna I tried, my results were the same. They were all deaf. Even my portable SW receiver couldn't hear anything. Any concrete building will do this.

For limited space I am a big fan of mag loops. For no bigger than they are they do a good job. Would a remotely tuned loop work for you? Something that could basically stay outside on a balcony and be tuned from an indoor operating position? I've heard of several hams who've done just that. You could pull the coax in for operating and any doors would almost be shut. Incidently I own the MFJ 1786 and use it, now and then, indoors in the woodframe house I now live in. I've worked both coast on 20 running 2 watts and on 10 I've worked a fair amount of europeans with band openings keeping power down to 25 watts. At 50 watts the S.O. came upstairs and asked "why is the paper shredder going off?"  Grin

Hey good luck.

DOC WB0FDJ
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KA2ZEY
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Posts: 78




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« Reply #6 on: May 01, 2013, 07:53:13 AM »

Ha! The paper shredder...love it! That's why I'll be staying with QRP...or maybe 12 watts  Wink

Yes, I'll look into having something like the MFJ Loop for the colder months or when I want to stay indoors. That seems like the best solution for small footprint operation. Those loops do work wonders.
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NW6V
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« Reply #7 on: May 01, 2013, 10:50:48 AM »

Hi Demian.

You mentioned that operating inside by a window did not work for you, others confirmed similar experience, and K7KBN compared operating inside an apartment to being inside a Faraday cage.

I would concur with K7KBN's statement, and perhaps expand on it. I believe operating near the window does not work because that window is essentially an aperture in the Faraday cage. Because the window (aperture) is very small compared to the wavelength of most HF operating frequencies, the waves cannot pass through. However, by the same reasoning, shorter waves, such as from an HT (or your KX3 when the 2M module is available :-), should pass though relatively unabated. If you have or can borrow an HT you could test this for yourself.

BTW, I've no idea where I read of this wavelength versus aperture size phenomena, but recall it. If others wish to provide a reference and confirm, clarify or debunk my understanding, please do so: I've no vested interest in it :-)

73, Chris NW6V
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W5WSS
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Posts: 1783




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« Reply #8 on: May 01, 2013, 11:14:23 AM »

Ok fine buisness, again the balcony antenna will respond to arriving skywave signals that are Not in the shadow of the building so that is half a circle around the compass.

As you want to use one of those MFJ loops weather permitting it will as you have already indicated hear and transmit.

I figured you could not hang, or said more accurately; attach an antenna wire to the top floor structure but you can slope a rigid small diameter tube angled upwards and outwards and attach a pair of radials routed around the balcony floor perimeter from perhaps the center of the balcony bulkhead rail? Does it have a screen preventing your aiming the rigid tube up and outwards?

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W5WSS
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« Reply #9 on: May 01, 2013, 11:18:13 AM »

And slope a Hustler with resonator and spend your time building a good horizontal radial system they do not have to be fanned to recover and return the current and voltage to the vertical to be radiated.
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KQ6Q
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« Reply #10 on: May 04, 2013, 01:44:17 AM »

If the mag loop works on the balcony, if you have the budget, get a remote tunable magnetic loop - MFJ makes two of them - one for 40-15m, the other for 30-10m.
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VE3FMC
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« Reply #11 on: May 04, 2013, 04:35:56 AM »

If the mag loop works on the balcony, if you have the budget, get a remote tunable magnetic loop - MFJ makes two of them - one for 40-15m, the other for 30-10m.

Leave the coax hooked up to the loops and when you want to operate open the balcony door and run the coax inside to the rig. If it is a sliding door which most apartments have, in the winter you can put some weather stripping along the edge of the door which would add some cushion and maybe come close to getting the sliding door shut all the way for heating purposes.
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W8LGZ
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Posts: 44




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« Reply #12 on: May 06, 2013, 03:58:38 PM »

Hi Demian,
Consider a couple of these antennas mounted on a short mast in a bucket of sand or concrete sitting on the balcony. Disguise it with some plastic foliage.
http://www.isotronantennas.com/

Good luck!
Jim, W8LGZ
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