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Author Topic: Need advice regarding antennas for restricted space.  (Read 5912 times)
KF5GFF
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Posts: 5




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« on: October 30, 2012, 02:09:17 PM »

All,

First of all let me start by thanking those of you who are taking the time to read my questions and in particular who are going to take the time to respond.

I have been an amateur radio operator for almost 15 years.  Recently I find myself living in a ground floor apartment in CO while I work on a year contract.  I would like to be able to remain active in MARS during this time (frequencies as low as 4Mhz) but the tight restrictions of my community give me little hope.  Angry

I need some advice and suggestions.

Here are the options I am considering.  Any opinions?

1.   TW2010 Traveler antenna with 80M coil
2.   Scorpion SA-680 Screwdriver antenna
3.   Buddipole
4.   Super Antenna
5.   Chameleon Antenna (CHA HYBRID Base plus V2L)
6.   A 30 foot Dipole with an SGC 230 Tunner
Obviously there are quite a few options here.  I am concerned mainly with visibility, RFI (it needs to be in close proximity to the building, and other electronics) and performance.

Thanks again,  Cheesy

Mark




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WB2WIK
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Posts: 20595




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« Reply #1 on: October 30, 2012, 02:37:36 PM »

Do you have a home station setup elsewhere, or have a good friend who does?

Many rigs now come with (and others can be adapted for) full control via the internet.  All you need is a "station" connected to the web, and a laptop with you.

I hear more and more "remotely operated" stations on the air every day.  If the operator doesn't tell you it's remote, you'd never know. Wink
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WX7G
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Posts: 6038




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« Reply #2 on: October 30, 2012, 02:46:36 PM »

If you provide links to the various antennas we can check them more easily.
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KF5GFF
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Posts: 5




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« Reply #3 on: October 30, 2012, 03:27:20 PM »

Here you go !!!!!!!!

Traveler:
http://www.twantennas.com/

Scorpion:
http://www.scorpionantennas.com/

Buddipole:
http://www.buddipole.com/

Super Antenna:
http://newsuperantenna.com/

Chameleon:
http://chameleonantenna.com/

SGC tuner:
http://www.sgcworld.com/230ProductPage.html
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AC4RD
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Posts: 1235




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« Reply #4 on: October 30, 2012, 03:50:09 PM »

Mark, just MHO, but don't BUY one of those expensive antennas.  Use a few bucks worth of wire hidden somewhere as a nearly-invisible doublet, feed it with twinlead from a tuner, and you'll have a better multiband antenna for a few bucks than you could buy for many bucks. 

There are tons of websites with information--google "ham apartment antenna" and you'll find many links!   GL!
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WX7G
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« Reply #5 on: October 30, 2012, 06:42:38 PM »

From your list of antennas there are two that allow instant band changes and stand out as having the best performance: the Scorpion screwdriver and the SCG tuner.

To drive a 30' dipole the SCG should have a 1:1 current balun at the output and from the specs it will tune the short dipole. If your MARS work is within a few hundred miles this might be the best antenna. With the SCG you are restricted to 200 watts PEP.

The Scorpion can be set on a tripod with a few 10' radials on the ground. It needs a 1:1 current balun to reduce RF current on the coax shield that will find its way into the apartment AC wiring. A longer whip such as the 108" from MFJ will help. You can even use the 17' telescoping MFJ whip but not in high winds. With this antenna you have the option of adding an amplifier.

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WA8FOZ
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« Reply #6 on: October 30, 2012, 08:09:07 PM »

Some good advice already here. It would help if we knew a bit more about your physical situation: how much room do you have, trees, etc.

All other things equal, the SCG tuner and as much wire as you can get up, center fed if possible, might be your most efficient choice. Maybe the least visible too. And likely the most height above ground - high is good. For the lower HF MARS activity, you really need some SIZE - the small antennas will be very inefficient at 4 MHz. Plus you have a great tuner for use after you move. My default would be a dipole, with fine wire - the Wireman and others sell 25 gauge insulated stranded copper-clad wire - great stuff, strong and hard to see. Make it at least 44 feet on each side, get the feedpoint as high as possible, feed with 300-ohm line, bend the wires around as necessary.

The Scorpion is a fine mobile antenna, but for it to work well as a stationary antenna, it would need a lot of radials. Buddipole and Super antenna are cute but tiny, and would be much less efficient than to Scorpion, and very inefficient below 20 meters. The Traveler is cool but not for below 20 meters. I will say nothing about the Chameleon.

Sounds like an interestimg project.
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AD0AE
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Posts: 78




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« Reply #7 on: October 31, 2012, 04:23:41 AM »

Hi Mark-

WA8FOZ mentioned that he would not comment about the Chameleon antenna, but I will.  I looked into it about 6 months ago.  Between the price and comments people wrote on eham, I would recommend you consider other options besides that antenna.  While I can't speak from personal experience about the antenna, it seems like there are better options for cheaper.

I will further echo what a few others have said, given the choices, I would probably go with some sort of invisible wire antenna.  There is a recent thread about that in the 'antenna restrictions' section.  That could give you some clever ideas. 

Another possibility you may want to try would be some sort of magnetic loop on the higher bands.

Good luck and 73s!
Steve
AD0AE
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WX7G
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« Reply #8 on: October 31, 2012, 05:22:29 AM »

Mark,

The #26 wire from The Wireman is quite visible with its black insulation. I've built "invisible" antennas using #32 wire from Radio Shack. But when frost hits it becomes quite visible.

I should add that I have operated from six apartments on bands from 160 to 2 meters. In three apartments the antennas were entirely inside the apartment and performance was good.

The MFJ-933 loop tuner would be great. The radiation efficiency should be around 25% with a wire loop and will beat the 5% (or less) of the Scorpion screwdriver.

I have an MFJ-933 I bought for experimentation and you are welcome to borrow it and give it a try. If you like it you can buy it from me or send it back to me and buy yourself a new one.
 
« Last Edit: October 31, 2012, 06:22:10 AM by WX7G » Logged
WX7G
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« Reply #9 on: October 31, 2012, 06:29:31 AM »

The loop can be inside the apartment and can be made from #10 wire or 1/2" copper tubing for higher efficiency. The MFJ-933 goes for $179 at Ham Radio Outlet.

The loop circumference can be 35 to 65 ft and a 36' loop can be configured as a 6' x 12' rectangle to fit inside an apartment.

Let's check that assuming the tuner can tune a 9' x 9' loop. With the bottom of the loop 2' above average ground, and made of #10 copper wire, the input impedance is 1.5 +j410 ohms. The 6' x 12' loop is 1.5 +j403 ohms. The tuner should be able to tune the rectangular loop.
« Last Edit: October 31, 2012, 06:52:45 AM by WX7G » Logged
AG6WT
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Posts: 448




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« Reply #10 on: October 31, 2012, 05:12:43 PM »

Mark,

I'd go with the SGC tuner and #26 polystealth. With the tuner you have the option of vertical, inverted-L, doublet, and loop configurations. I have a similar tuner, the Icom AH-4, and have set it up as a vertical and inverted-L with polystealth. My support is in the lot corner so I haven't tried a doublet but others have. You can find examples with Google. The #26 wire is practically invisible. Presently I have it configured as a delta loop that tunes 80-10 meters. It hears and gets out pretty well considering my restrictions.

The other solutions are as or more expensive, lock you into one antenna type, and are less efficient than a full size antenna.

Ray KJ6AMF
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KT8K
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Posts: 1490




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« Reply #11 on: November 16, 2012, 06:19:48 AM »

I'm going to write a short book here - sorry ...
RFI will be your biggest concern in an apartment building, and I wouldn't even consider an amplifier.  Even 100 Watts will cause issues, and revealing your operations to your neighbors could bring the management down on you, a good thing to avoid.  You need the highest efficiency antenna possible, and you will be able to use the SGC tuner in many circumstances. I think that is probably your best investment.

If you can get >60' of wire stretched up into the air it will tune 80m with good efficiency and may reach 90% if you can put out a couple of wire radials. Radials can be stretched along the building walls in any arrangement - straightness is not that meaningful.  Burial will hide them, but If you can staple or glue or otherwise fasten the radials to the building wall even a couple of inches above ground level you can get away from a lot of ground loss - a big improvement.  A couple of elevated radials will equal or outperform many buried radials, so this is a good thing to do.  Radials can be run up and over doorways without harming antenna performance much, too. Elevated radials have to be cut to resonance, though, so at least one per band is advisable (though a 33' radial for 40m will also be usable for 15m).

Think creatively.  Getting the antenna away from the building is best from an RFI perspective but you may not be able to do that.  Here are some examples I have run across:
- a long wire of 40 gauge magnet wire (REALLY invisible) tossed over a tree and tuner-fed against a ground rod behind flower beds.  When the wire broke he would pull as much of it out of the tree as possible and toss a new one up - that happened once or twice a year.  Another ham did the same but was on an upper floor with no way to use a ground rod, so he grounded to everything conductive in the area - the balcony railing, the frames around his sliding glass doors and windows, etc.  (Just don't be transmitting above 5 Watts or so if someone has their hand on the window frame!) 
- One ham used an aluminum downspout as his vertical, tuned against a ground rod.  He managed to get up to the gutters with a ladder one day and bonded more sections of the gutter system by putting sheet metal screws between them to ensure a good electrical connection.  Another ham had plastic gutters, but managed to stretch some wire out in the bottom of the gutters and ran his feedline down a handy downspout, recognizing that he might have to re-do it if management ever cleaned the gutters.
- One ham stapled a loop of 22 gauge hookup wire under the eaves of the building, all the way around, and fed it with a short section of ladder line down to his autotuner - it worked great.  He chose the color of the wire to blend in, and I believe he painted the ladder line.  While this might affect the impedance of the line, it's not a big hit on performance, and stealth is more important in an apartment situation.
- Other hams have tried tuning the wiring of the building, but this is a great way to create terrible RFI.  Also, ductwork, wiring, and building structure can parasitically soak up RF and kill your antenna's performance, so even getting it outside the wall or (better yet) more than a foot from the structure can make a BIG improvement.  I had an indoor dipole, and then a loop, that worked terribly in my house.  I changed to a 40m dipole thrown over the roof, but it was still terrible.  Then I managed to use a nearby tree to get it just a couple of feet above the roof and I was suddenly making lots of QSO's.  I believe the ridge vent, a metal screen running the length of the roof peak, was killing performance until I got away from it.

There are a bunch of ideas.  Good luck, and I hope to catch you on the air soon.  73 de kt8k - Tim!
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LA9XNA
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Posts: 107




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« Reply #12 on: November 17, 2012, 02:21:11 AM »

Why dont you try a magnetic loop antenna.
If you put it on a moable stand you can stow it away when not using it and the importance of invisibility is not that important.
Have a look at thest two links to give you an idea of the loop.
http://www.66pacific.com/calculators/small_tx_loop_calc.aspx
http://www.cvarc.org/tech/magnetic_loop_antenna.pdf
Most of the parts you will rewuire can be bought in a hardware store.
The hard to get part is the tuning cap but they can be found in fleemarkets, junksales and many of the online sales pages.
The most important thiong about the tuning cap is to ensure that the voltage rating is high enought so go for ht highest rating you can afford.
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WX7G
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« Reply #13 on: November 17, 2012, 10:09:04 AM »

A magnetic loop antenna was suggested in an October 31 post. MFJ builds a tuner specifically for this.
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W7MJM
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Posts: 109




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« Reply #14 on: November 17, 2012, 04:07:36 PM »

The #26 wire from The Wireman is quite visible with its black insulation.

WX7G must have better eyesight than I have!  Smiley  I've had good luck with the insulated #26 copper-clad Davis RF "polystealth" wire from HRO, which is similar to the Wireman product. I used it to make a full-wave 40 meter sloping delta loop, with its apex about 40 feet high, supported by a palm tree. The wire is visible, if you know where to look for it, but otherwise, I think most folks wouldn't notice it. Not quite as "invisible" as magnet wire, but it'll stay up there a lot longer and the birds won't fly into it! Indeed, the local humming birds like to rest on it. From across the street, the hummers look like they're hovering in mid air, until you notice that their wings aren't moving!

73 and good luck with your antenna plans,
Martin, W7MJM
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