++++++++++++++ From: "Greg White" To: Date: Sat, 21 Sep 2002 13:01:54 -0400 Subject: [Elecraft] Attic Antenna Tradeoff? I am currently building a new home and have many challenges regarding the use of a traditional outside antenna. I know that an "indoor/attic" antenna is a compromise, but how much of one?? All things being equal, what amount of attenuation (receive and transmit)can I realistically expect? I am just trying to figure out if I would be happy with an attic antenna for the time being. I will use a trap dipole in the attic (about 25-30 feet) with my K2. Thanks! Greg, N9EYO +++++++++++++++ Date: Sat, 21 Sep 2002 14:31:00 -0400 From: Jim Campbell To: Greg White Cc: Elecraft Subject: Re: [Elecraft] Attic Antenna Tradeoff? Greg, One of the truisms of antennas is that any antenna is better than no antenna. I have been using an attic antenna for over a year with my K2 and have been quite happy with my results. I live in an antenna-restricted neighborhood and the attic antenna is my only choice. I tried a loop stapled under the eaves for a while, but it didn't work all that well. For most of its run it was only a few inches from an aluminum gutter. There has been a lot of controversy on this list and the QRP-L list about 88-foot dipoles. That is what I am using. The center of the dipole is fastened in the center peak of my attic. From there it runs to the eaves at each end of the house. From there it goes vertically outside the house for a few feet where it is then tacked to the side of the house. The outline would be something like the cross-section of a circus tent. I feed the center of the dipole with 300-ohm twin-lead. The twin-lead runs to the top of one of the interior walls of my house. From there I use coax down through the wall to the operating position. I use a choke balun where the twin-lead joins the coax. My KAT2 has been able to load this antenna with an acceptable SWR from 160 meters - 10 meters. I have talked with Russia, Croatia, France, Germany and England. The other direction I have talked with Alaska. That is all using 5 watts CW. For the most part, if I can hear them, I can work them. I am located in Raleigh, in the central part of NC. If you have any questions, just ask. 72, Jim W4BQP ++++++++++++++++ From: JimWMiller at aol.com Date: Sat, 21 Sep 2002 15:33:04 EDT Subject: Re: [Elecraft] Attic Antenna Tradeoff? To: whiteleto at myvine.com, elecraft at mailman.qth.net Cc: kn2x at webtv.net Greg, I've used a commercial parallel dipoles in the attic for years and was reasonable happy. Recently I've set up an outdoor w9inn dipole with loading coils. To make a long story short, on 80 meters the outdoor was much better but on 40 and above the indoor was almost as good. Some actual results from a comparison of the two antennas follows: band indoor outdoor 80m S9 20 over 9 40m S7 S8 20m S4 S5 A good 40 meter antenna in the attic is *almost* as good as an outdoor. Keep the power levels down to 20 watts or less for an indoor antenna! GL & 73, Jim WA2UMP K2:2679 ++++++++++++++++ Reply-To: From: "Ron D'Eau Claire" To: Subject: RE: [Elecraft] Attic Antenna Tradeoff? Date: Sat, 21 Sep 2002 13:14:26 -0700 I spent a decade living in apartments and working QRP with an HW-8 using "indoor" antennas. I had a lot of fun and a lot of contacts on 40, 30, 20 and 15 meters (I had converted my HW-8 for 30 meter coverage instead of 80 meters). In each case, I was selective about my apartment. I chose a wooden building and got on the second (top) floor. I was able to access the "attic" crawl space above my apartment, although all well-built apartments have fire/security partitions in the attic that limited my access to the space directly over MY apartment. Still, I was able to put up a doublet (center fed "dipole" of indefinite length) of 45 to 60 feet with some bends near the ends. I hooked it directly under the roof rafters as high as I could go, so the center was at the peak of the roof gable. I used GOOD insulators. No need to waste any extra RF. Also, I took care to stay as far away from metal ductwork and house wiring as possible, although that was only a matter of a few feet away in most cases. Also, I crossed the paths of conductors at a near a right angle as possible to minimize inductive coupling. It was fed with "open wire" line crafted by using two lengths of white hookup wire separated by lightweight plastic insulators (not many required - no breezes, etc. to twist them in the attic). I took an "ice pick" and punched two small holes in the ceiling next to the wall directly over the "shack" location (a desk situated strategically as near the center of the apartment as was practical). The white wires ran down the apartment white walls and were so invisible visitors had to be shown them to see them. The rig sat on the desk where they ended. Used a small transmatch to load it up. I was never short of QSO's at QRP power levels, even DX when 20 or 15 was open. Never had RFI issues at that power level either. A couple of observations: I noticed that noise levels were very high on 80 and below with that antenna. No surprise with apartment buildings full of cheap dimmers and other RFI-generating devices. By and large 40 meters was fine, once I silenced the cheap dimmers in MY apartment. 20 and 15 were great, since the antenna at about 20 feet up was a decent height for a good radiation angle for 20 and up. At one apartment my luck raising stations got worse during wet weather. Trying to get out on VHF using an attic mounted J-pole was useless. That apartment had a slate-like tile roof (not my first choice, but the choices were limited). One day I saw a piece of one of the tiles on the ground, left by someone working on the roof. On a hunch I took into my apartment and put it in the microwave for 30 seconds. It was toasty hot. It had a LOT of metallic content apparently, because it was quite dry. No apparent steam or other evidence of water. In one apartment with "cathedral" ceilings, I simply ran an end-fed wire white wire (again invisible) along the highest point of the ceiling and loaded it against a 1/4 wave 'counterpoise' along the baseboard - running pretty much in the 'opposite' direction. It worked as well as the dipole, I think but needed a resonant counterpoise. When I got a slingshot and fired a lead weight with a length of nylon leader over a tree out back so I could run the wire up from a window into the tree (taking care that the far end was clear of the foliage) it worked even better! As another op pointed out, ANY antenna is better than NO antenna! Ron AC7AC K2 #1289 ++++++++++++++++ From: "Doug Person" To: "Greg White" , Subject: Re: [Elecraft] Attic Antenna Tradeoff? Date: Sat, 21 Sep 2002 16:44:09 -0400 Greg, I have dipoles in my attic for 40,20,17,15, and 10. The 40 uses two loading coils in either leg to reduce its size by about 60%. I have no trouble getting out on all bands and performance is just slightly worse than my outdoor dipoles. A more important problem is that the indoor antennas pickup considerably more noise from the usual assortment of electronic devices in the house. This was the main reason I eventually put up antennas outside. The bottom line is that if you are really limited to attic antennas - don't worry you'll do fine. If you can possibly put up a dipole outside - do it. It'll be a lot quieter. I use a W9INN - 60 feet - 5 bands 80-10 - works great and not very visible with the trees behind it. I also use a Spi-ro D-314 3 band trap dipole for 30-17-12 and it works very well. Two antennas and 9 bands. Doug -- W4DXV ++++++++++++++++++ From: "Bob Tellefsen" To: "Greg White" , Subject: RE: [Elecraft] Attic Antenna Tradeoff? Date: Sat, 21 Sep 2002 16:44:15 -0700 Greg The main thing with an attic antenna is to keep it as far as possible from house wiring, plumbing, sheet metal, etc. It wants to be in the clear as much as possible. Since house wiring is often covered with attic insulation, you will have to do a little checking to see where the wires are actually run. If the antenna couples too closely into house wiring, and you run 100 watts, sometimes you can actually see ceiling lights blink, even when turned off. Happened when my father-in-law visited us. We hung a dipole across his room at ceiling height, and boy, did the light blink :-) That's all "talk power" that is wasted. Good luck and 73, Bob N6WG +++++++++++++++++ Greg, When I first started working HF, I was more worried about the YL than any neighbors. (I have thick woods all around the back yard so, they would never see an antenna.) Not wanting to get on the bad side of SWMBO "She Who Must Be Obeyed" I put up a "slinky" antenna in the attic. I worked L.A. on 75m phone with that antenna from here in Ohio, during the daylight hours even if I remember correctly. Now, that said, let me go on to say that the antenna was still _terrible_ and I mean *BAD*! The noise floor was a good 3 s-units above the current dipole I use. Additionally, the RFI (tv, phone, etc) was bad, even at 30-40w and it was a bear to tune up the thing. I'm pretty sure that the noise/tuning problems can be attributed to HVAC ducting (metalic) and power wiring that lay below the insulation in my attic. After a few months of frustration, I put up a 135' dipole at about 20ft in the back yard and carefully hid the coax run coming into the house. The guys I had been talking to for a month or so in the evenings accused me of buying an amplifier and man did the dipole hear better, on every band! So, IMNSHO, attic antennas (or at least slinky's) are _serious_ compromises. I think I could have done better by loading up the rain gutters! If you've got _anything_ to use as supports, you can put up an antenna that is very hard to see. I use 12guage wire for my antennas and I have a hard time finding them in the air, and I know _exactly_ where to look! 73 de John - KC4KGU K2/100 #2490 +++++++++++++++ Hi Greg I've used a magnetic loop in the loft of my house, I guess the height was about 25 foot above ground level. On 14 to 28 MHz there appeared to be little attenuation when comparing the loop to an outdoor dipole at a similar height. The roof has concrete roof tiles. I wouldn't recommend a magnetic loop as you have to re-tune them every few KHz. When staying in hotels, I sometimes take a 22 foot fibreglass fishing pole and use it to hang an end fed wire from a window, around 36 foot of wire tuned against a pair of counterpoise wires (33 and 16 foot) seems to tune OK on my four band K1 with KAT1 (40/30/20/15). So you could experiment with a temporary fishing pole from an upper floor window! 73's Dave, G4AON K1 #1154, K2 #1892 +++++++++++++++++ From: "Rod N0RC" To: "Greg White" , Subject: Re: [Elecraft] Attic Antenna Tradeoff? Date: Sun, 22 Sep 2002 06:44:11 -0600 Greg, Add me to the Attic Ant "user group". Mine is a multiband doublet, details at: http://www.radioactivehams.com/~n0rc/antennas/ I've worked stations all around the world, and place well in QRP contests/sprints I sometimes enter, usually top ten or 20. I really can't give you a good measure for outdoor verses indoor ant my QTH, never had an outdoor antenna up long enough to make meaningful measurements. I can say that it works better than no antenna, and given CCRs (Concentration Camp Rules ;-) no outside antennas, that is saying something, I guess. Some advice I will pass along: Have your attic insulated with "Batt" type material, not the spray-in stuff. Walking around/working in a attic full of spray-in stuff is miserable. Also, consider adding 1 or more 2-3" DIA plastic conduits for cable runs, and maybe add some "catwalks" in the attic to facilitate moving around. GL, 73, Rod N0RC ++++++++++++++++ From: "Ferguson, Kevin" To: "'elecraft at mailman.qth.net'" Subject: [Elecraft] Attic Antenna Tradeoff? Date: Mon, 23 Sep 2002 17:08:36 -0600 Most of us are just stuck with what we ended up living in, NOW is the time to be thinking about this, Good Job! Specify that the attic is NOT to be used for electrical, phone, CATV, HVAC control etc. wiring, except as required for cieling fixtures etc. This will cost more, as the attic is the easiest place to run the wires. One of the huge problems with attic antennas is that they invariably end up closely spaced and significantly paralell to AC wiring runs. This couples all the RF hash on the wires into the antenna. Since the lines are connected to the grid at all times, it is not just garbage generated by a load on that line that couples, but also from things connected several miles away. The more wire you can keep out of the attic, the better. Keeping phone, CATV lines out of the attic also avoids RFI issues. Even the HVAC control can get RFI. I get RFI into my thermostat if I run over 5W on 10 meters....this turns the furnace on and off with my keying and eventually puts out the pilot light. Other things to think about: Architectural: If you live in New-England or other areas with heavy snowfall, then the building code probably requires a steep pitched roof....this is very good, as it lets you put your antenna higher, and you will be able to walk in the middle without stooping. If you live in a moderate climate, then you may want a steeper pitch than the minimum required by code. Insulation: Specify that no foil-backed insulation is to be used in the house. If it is more than one story, such may be acceptable on the lower floors, but not on the upper floor. The warning against blown-in attic insulation is valid. That stuff is a royal PITA. Siding: No aluminum or steel. No stucco (has expanded metal or chicken-wire embedded). Roofing: Of course steel roofs are a no-no. If using composition shingles, specify that the valleys are to be full-woven, with 90# felt (roll roofing) under them. Otherwise you will get long metal flashings in the valleys. I don't know of any alternative to metal edge flashing, but ask about that. Rafters: See what it would cost to have traditional rafters fabricated on site. Pre-fabricated truss style rafters are probably cheaper, but really make it hard to move about the attic. The jew plates at the joints invariably end up within inches of your antenna. There are some "engineered lumber" (wood I-beams) out now, that if used as cieling joists may make the cost a wash. Specify that all the water piping should be copper (handy for grounding) Have an attic-stair access hatch installed when the house is built. You don't want to be climbing through a small trap-door on a regular basis. Mechanical: If possible, no metal ductwork in the attic. If possible place furnace and H2O heater near edge of structure instead of the middle. If the metal vent flues go up the middle they will be in the way of everything. Use PVC for sewer vent stacks...possibly with a short metal section where they go through the roof. ++++++++++++++++