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Author Topic: Outdoor vs. Attic Antennas  (Read 4386 times)

Offline Hitchhiker

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Outdoor vs. Attic Antennas
« on: July 05, 2014, 1614 UTC »
I'm a very new beginner at the SWL and MW dxing hobby and in need of all sorts of info. This forum has been an excellent help (many thanks to Glimmer Twin) but there are still a few things I'm trying to figure out. Mostly about antennas. Read through some of the previous posts ("Gear required to take the next step" & "Educate me about antenna choice") but still have a question that wasn't addressed directly: attic vs. outside antennas.

I hear HF hams talking about attic antennas they use to transmit, but has anybody used one specifically for SWL dxing? Most everybody in the forums seem to have slopers, loops or simple wires, and I plan on getting a loop for MW dxing. I'm on a small lot and could get a sloper to work but it'll take some doing. An attic antenna would be more convenient to set up but would it be any good for straight-up listening? It it an option or should I concentrate on getting a sloper to fit?

Whichever one it is it'll need to work well here in Texas, in the dead center between both coasts. I'm still plotting out an overall setup and am leaning toward the Satellit 750 as a receiver to start but even that choice is still up in the air. But it's the antenna decision that's making me nuts. Any and all advice, as well as critiques, are welcome.

Hitchhiker

Offline ChrisSmolinski

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Re: Outdoor vs. Attic Antennas
« Reply #1 on: July 05, 2014, 1644 UTC »
For receiving, an outside antenna is preferably to an inside/attic antenna for a few reasons:

First, an inside antenna is more likely to pick up interference from electronic devices in the house. Computers, TVs, appliances, switching power supplies on virtually everything today, etc. This isn't a problem for transmitting, of course.

Second, the received signals can be attenuated somewhat by the house itself, especially if there's a lot of metal. If you've got aluminum siding, you're might essentially be inside a Faraday Cage.

Third, with an outside antenna, you probably have a better chance of getting it higher in the air, if you have a lot of tall trees in your yard.

Fourth, you can usually have a larger antenna antenna outside.

This is not to say that an antenna in the attic can't work, just that you'd probably get better results from one outside.  What are the dimensions of your lot, and where you do have trees?
Chris Smolinski
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Nella F.

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Re: Outdoor vs. Attic Antennas
« Reply #2 on: July 05, 2014, 2312 UTC »
If you've got aluminum siding, you're might essentially be inside a Faraday Cage.

                     So since my apartment has an aluminum roof I'm inside a Faraday Outhouse?
                                                        Yeah, I like that!
                                   Regretting your choice of pill yet,  8)  Mr. Anderson?
« Last Edit: July 05, 2014, 2344 UTC by Nella F. »

Offline Pigmeat

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Re: Outdoor vs. Attic Antennas
« Reply #3 on: July 06, 2014, 0118 UTC »
If you've got aluminum siding, you're might essentially be inside a Faraday Cage.

                     So since my apartment has an aluminum roof I'm inside a Faraday Outhouse?
                                                        Yeah, I like that!
                                   Regretting your choice of pill yet,  8)  Mr. Anderson?

So you bought the old Fansome place, eh Nella? How's Capt. Ron's box holding up?

Hitch, 30-40 feet of wire going out the window to a nearby bush/tree will work fine. Keep it up high enough so the neighbors don't get tangled up.

You can try other types of antennas as you gain more experience.

Offline Fansome

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Re: Outdoor vs. Attic Antennas
« Reply #4 on: July 06, 2014, 0301 UTC »
Pigmeat's advice, I'm pained to say, is actually pretty good. At my last QTH we used magnet wire as an outside antenna. It was almost invisible, and very cheap, making replacement easy. We used a ball of clay as a weight to throw it up into a tree, and just let it hang over a limb. This allowed the antenna to slide on the limb in heavy winds, rather than breaking. Of course, eventually the clay would fall off; after a year or so the ground underneath the tree began to look like a dog litterbox.

When I lived in the SF Bay area I had a longwire in the attic, just regular stranded copper, connected to an MFJ tuner and from that to my DX440. The wire was probably 40' long or so; the roof was asphalt shingles. I never really heard any pirates, but it worked well for broadcast, ham, and utility stations. Again, it was a pretty cheap setup.

Offline glimmer twin

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Re: Outdoor vs. Attic Antennas
« Reply #5 on: July 06, 2014, 1316 UTC »
I've found that the 30 or so feet of wire that I have running out my 2'nd floor bedroom window to a tree performs pretty much as well as the Alpha Delta sloper I shelled out for. I used to have an attic antenna & it worked fairly well but outdoor is almost always better.
I've had good luck using odd things as an antenna also. Look around your house & yard & maybe try using a chain link fence or the gutters on your house (assuming they aren't plastic) or downspouts. I use the stop signs in my neighborhood as what I call inductive coupling stations when I am going portable & want to try to ID a pirate. Just try stuff & see if it works.

good luck
« Last Edit: July 06, 2014, 1503 UTC by glimmer twin »
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Offline Hitchhiker

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Re: Outdoor vs. Attic Antennas
« Reply #6 on: July 06, 2014, 1601 UTC »
This is all excellent advice. Thanks for the help and especially for your patience. Something tells me this won't be the last elementary question I'll ask.

What y'all say about the attic antenna was really what I expected. The interference would probably make it all but useless. I'm sold: make it easy and go with the longwire. There's a guy at a local ham group that uses Fansome's tree method only he uses an eyescrew in a softball instead of clay. Either way, it'll do the trick with the black walnut tree in the backyard.

And now for the follow-up. While I don't live in Nella's Faraday Outhouse, I do live in an 89-year-old house where the windows were painted shut back during the Reagan Administration. So unlike almost everybody I can't just toss a line out the window. I'm considering two options: (1) run it through the vents to the crawl space under the house, up a wall and out through an old, unused phone jack; or (2) run it through the soffit vent into the attic then down the wall to the unused jack. The extra work doesn't worry me, but I'm concerned about how that would effect the signal. The soffit seems an unlikely choice because it is metal. But will running the extra line (10-15 ft.) through another part of the house mess up the signal as well?

Offline ChrisSmolinski

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Re: Outdoor vs. Attic Antennas
« Reply #7 on: July 06, 2014, 1714 UTC »
Every section of your antenna that is inside your house can pick up interference from inside devices. That's why it is common to use coax between the radio and the start of the antenna. While some sort of a matching transformer (such as a unun) may be ideal where the coax and antenna meet, they aren't required, and many listeners do fine without one. Just connect the antenna wire to the coax center conductor. Some weather proofing would be a good idea, so water doesn't get inside the coax. Some advocate grounding the coax shield at the antenna, others say leave it open.

Note that you should have a lightning arrestor or other protection device for any outside antenna, which should be grounded, for safety. Personally, I take the extra step of disconnecting antennas when storms are likely.  The NEC (National Electric Code) has a section on dealing with antennas and transmission lines, IIRC, which you may want to consult.
Chris Smolinski
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Offline BoomboxDX

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Re: Outdoor vs. Attic Antennas
« Reply #8 on: July 07, 2014, 0233 UTC »
Worse comes to worse, I've heard of guys using flat metal plates / aluminum tape / something similar on each side of the window to get the signal from an antenna into a a room through a sealed window. Some sort of capacative transfer / proximity effect from the antenna's plate on one side of the window to the piece of metal on the other side.

Also, if your windows are aluminum framed, you can use the frame as a connector -- attach the outside wire to the frame, and then attach your feedline from the radio to the frame also.
An AM radio Boombox DXer.
+ GE SRIII, PR-D5 & TRF on MW.
The usual Realistic culprits on SW (and a Panasonic).

Nella F.

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Re: Outdoor vs. Attic Antennas
« Reply #9 on: July 08, 2014, 0103 UTC »
Humm, o.k. seriously here now, I've mentioned this before. There is a 6 or 7 foot long baseboard heater (attached to the wall) in the back bedroom. I use an 8 foot long wire with an alligator clip running along the floor attaching to the radiating louvers & connected to my R8B. It works surprisingly good. For pirates. Don't even ask me why. Also have "longwires" attached to ceiling which work better for 25-13 meters. The back bedroom faces an empty lot N. Northeast. Again & I can't stress this enough:
                                                      Don't even  8)  ask me why it works.

Offline Hitchhiker

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Re: Outdoor vs. Attic Antennas
« Reply #10 on: July 08, 2014, 0237 UTC »
BoomboxDX, you've caught my imagination with the two metal conductors on a window idea. Do these guys use any particular type of metal (such as copper) and how much metal do you think that would that require? Big piece, small piece? No aluminum on the windows so the metal plate is a real possibility. But I'll be open-minded about it and see if I can recreate the magic of Nella's Faraday Outhouse.

Offline BoomboxDX

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Re: Outdoor vs. Attic Antennas
« Reply #11 on: July 08, 2014, 0540 UTC »
I don't know what kind of metal they use. I read it in an article a long time ago, unfortunately.

I would think that any conductive metal would work. Maybe even aluminum from cheap cookie sheets or aluminum pie plates. It would at least be worth a try.

The proximity effect is a very real effect -- I used to take the whip of one of my most noise reducing radios (a Panasonic) and place it within a centimeter or inch or so of my longwire feedline and could still listen to Shortwave with the radio that way.

I think the metal plate thing works the same way.

I just did a search for through the glass window antennas, and a few things that come up say that the antennas work, even for transmittting (although they don't work so well for transmitting on HF -- but as you're not transmitting, that shouldn't be an issue).

Here's a link to a company that sells through-the-glass mobile antennas for 2 meters:
http://www.kenneke.com/antennas.html

Probably you'd want larger plates for HF. But the principle should work the same.
 
An AM radio Boombox DXer.
+ GE SRIII, PR-D5 & TRF on MW.
The usual Realistic culprits on SW (and a Panasonic).

Offline Token

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Re: Outdoor vs. Attic Antennas
« Reply #12 on: July 09, 2014, 1344 UTC »
Worse comes to worse, I've heard of guys using flat metal plates / aluminum tape / something similar on each side of the window to get the signal from an antenna into a a room through a sealed window. Some sort of capacative transfer / proximity effect from the antenna's plate on one side of the window to the piece of metal on the other side.
 

Years ago, when living in an apartment with single pane windows that I could not modify, I did something similar to the above.  I got some copper foil tape, about 2 inches wide, from a hardware store.  In a lower corner on the inside of the window I made a square section about 10 inches on a side, completely filled in with the copper tape.  On the outside of the window I made an identical area covered with tape.  The windows had metal frames.  Inside I ran coax from the radio to the window, and connected the center conductor to the tape square, the outer conductor to the metal window frame.  Outside I connected coax the same way, center conductor to the tape and outer to the frame.  I ran that coax to the location of a magnet wire random wire.

It worked quite well, although I am sure there were some serious impedance issues.

Aluminum tape is probably easier to find, I bet every Lowes and Home Depot has it for duct sealing, but copper is easier to make a good electrical contact since it is easier to solder.

T!
« Last Edit: July 09, 2014, 1346 UTC by Token »
T!
Mojave Desert, California USA

Offline Tom S

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Re: Outdoor vs. Attic Antennas
« Reply #13 on: July 09, 2014, 2127 UTC »
What you're doing when you use metal plates or tape on two sides of a window is making a simple capacitor.  It should work fine for SWL'ing.  I'm sure aluminum foil would work OK too, but would be hard to attach the coax or lead-in wire to.
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Offline jFarley

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Re: Outdoor vs. Attic Antennas
« Reply #14 on: July 09, 2014, 2151 UTC »
TomS speaketh the truth.  I was interested in seeing what effect running RF thru a homebrew capacitor such as this would have, so I ran some numbers at work.

K&S Engineering has little displays in many DIY and hobby stores where you can get small pieces of metallic plate.  In mine, they have a 4" x 10" x 0.025" pure copper sheet for around $7 (pricey, but I am sure you could probably do better online) so I used this as the basis of a design.  Aluminum foil would probably also work in a pinch but with greater difficulty in making solid and stable electrical connections.

Two 4x10 plates separated by a thickness of single strength glazing glass (about 3/32" thick) will create a capacitor of roughly 760 pF.  At 7000 kHz, this capacitor will have an impedance of 30 ohms.  For a receiving system, the effect will most likely be minimal in bringing in the signal from a wire receiving antenna.  At lower frequencies, you might want to use proportionally larger plates.

Prior to actually making a feedthrough, you could always do a simple test by placing a resistor of roughly 30 ohms (or a cap of 750 pF) between the antenna and the receiver feed and seeing if you could live with that.
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