Wayne, you can put up an outdoor antenna for precious little more money than that attic antenna. I'd recommend doing that if at all possible. After all, it's just wire. Even an end-fed random wire is likely to work better than anything indoors. As for the dreaded "counterpoise", try to make your antenna at > 1/4 wavelength on the lowest frequency band you'll use (longer is better) and you won't need much of a "counterpoise". Perhaps a 1/4 wavelength long wire on the lowest frequency band running along the baseboards or outside along the side of the house.
BACK IN THE ATTIC I've used attic antennas in many places. In my case I was an apartment dweller for a few years so I made a point of renting the top floor apartment (usually second story) and figuring out how to get into the attic space above. (There usually is an access through a closet ceiling somewhere). I always put up a doublet - a center fed wire of whatever length I could squeeze in. I ran it along the highest place - under the ridge board just under the shingles. That put it as far as possible from wiring, ducts, etc. It can zig-zag somewhat, but I strived to keep the two halves pretty symmetrical. Frequently I ran the length of the ridge board (which in an apartment was usually about 30 feet or so between the security/firewalls that to go the roof between each apartment) then run down at the ends to the eaves - one end went one way the other end went the other for maximum separation. (That's an easy outside antenna too.) I insulated the ends where there will always be a high impedance. A bit of plastic bottle with holes punched in it works FB. But doing that helps avoid more unbalance and losses. (Insulators made from scrap bottle or clothes hangar plastic will work FB outdoors too.) For "feedline" I used two small-gauge white wires (apartment walls are invariably white). Plastic-bottle-bit spacers handle the run in the attic to a point directly over my operating desk. A fine pointed tool (e.g. ice pick) made two small holes in the ceiling right against the wall above the operating desk. The white wires come down the wall - held with a couple of staples - right to my ATU. The feeder was virtually invisible. One visitor at the desk kept asking where the feed line was. It ran up the wall 2 feet in front of his face. A balun isn't strictly necessary. Just connect one side to the rig case and the other side to the center conductor. Yes, it will be somewhat unbalanced. The only downside of that is that the feeder will radiate, but it's not a very long feeder. If you notice some "hand effects" (touching the radio changes SWR, etc.) try a balun. Elecraft has some great baluns that do well in that use. The issue with baluns is that they can become lossy at extreme impedances, and you can't really predict it too well in that environment. But many hams use them with excellent results. I had a homebrew balanced tuner on my system. ROOF You mentioned asphalt shingle roof. Excellent. I had great success radiating through those. In one apartment I couldn't get out worth a darn. One day I noticed a piece of tile from the roof. The building had concrete tiles. Put it in my microwave (with the obligatory glass of water) for a couple of minutes and that tile got smokin' hot. Concrete is a better conductor than the earth - or perhaps better said that it's a better lossy dielectric than the earth. In either case it did a bonza job absorbing my RF. QRO? I ran up to about 15 watts output in my apartment environments. Worked a lot of stations and a far share of DX - enough to keep it interesting - all CW. Even 15 watts got into our telephone but I was able to squelch it. I chose not to run more power so I'd not have to worry about neighbors sound systems, etc. Ron AC7AC -----Original Message----- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Wayne Conrad Sent: Monday, April 11, 2011 4:12 PM To: elecraft@mailman.qth.net Subject: [Elecraft] K2 + ATU + Loop antenna in the attic My radio (K2 with the internal ATU) hasn't shipped yet, but that shouldn't stop me from putting up an antenna, right? If only I knew what to put up, that is. That's where I'm asking for help. I want to start out with an loop antenna in the attic. Why loop? Mostly the very American idea that more wire must be better, plus it's balanced--I hope to not need a separate RF ground, or counterpoises, or any of that jazz). Why the attic? So I don't have to worry about lightning protection, and because it ought to be incredibly cheap to put up. I've spent every dime I have on the radio, you see. The house is the usual ~60' x ~30 feet and "L" shaped, single story, and the major axis is North/South. The attic is full of trusses and fiberglass, but I can get to most of it, sometimes slithering on my belly like a snake. There are the usual electrical wires, network cabling (OK, maybe not everyone has CAT6 in their attic), TV coax, and AC ducts going hither and thither. My shingles are asphault. I have no idea what band or bands I'll be on. I don't even have my license yet. My thought is that I run the loop around the perimeter of the attic, as close to the eaves as possible. Over the radio bench, I'll punch a hole in the ceiling and drop feedline down the wall. I was thinking of open-wire feeder, because I "read on the internet" that it might be better for this application. It occurs to me that I could omit the 4' of feedline and just drop the two wires down. Using the self-adhesive conduit that the hardware store sells, I could keep those two wires at "an appropriate distance" from each other, and white conduit looks better against a white wall than a black cable. I don't know if that's a good idea, or what "an appropriate distance" would be. I don't know if I need a balun, or even what kind. I don't know whether I need to keep the antenna wire off of the rafters with insulators, or can I just let it lay there. Nor do I know if the answer to that question changes if I eventually go QRO. I don't know if the length of the loop matters. As you can tell, the ratio of things I know to things I don't know is pretty small. Can you please help me improve that ratio? Thanks, and best regards, Wayne Conrad ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
