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#1
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Andy writes:
I would like to hear some discussion/advice on the feasibility of putting an antenna for, say, 30m in the attic versus on top of the roof... Here is the situation : The roof peak of my house is about 50 feet and is straight. Given the need for a dipole which is 44 feet wide, it can be mounted in either of two places: 1) Just above the roof peak, straight along it, about 1 foot above. 2) Just below the roof peak,inside the attic, about 1 foot below . Let's assume there are no other options... So it sort of boils down to whether the wood and asphalt barrier , free of metal except for an occasional nail, actually attenuates the signal enough to bother about, or affects the antenna impedance enough to bother about..... Having made dozens of ham antennae over the last 40 years in configurations that probably violate the laws of physics and having had them work, I, personally, haven't found that such a difference in the antenna placement makes a hill of beans worth of REAL difference (no pun). But a lot of guys here have been doing this for 40 years also, and I'd really like to see what anyone has to say about it..... I generally use one rule of thumb on antennae: " If when I connect the antenna to the receiver, the background noise of the receiver increases, the antenna is doing a good job"..... Yeah, I know, but it needs some thinking about because if the cosmic noise level picked up by the antenna is higher than the receiver noise level, then it has to be working........assuming it is cut to the proper frequency for the band used..... So, what about it ? Anybody want to put in their two cents worth ? Andy W4OAH |
#2
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ORIGINAL MESSAGE:
On 10 Dec 2006 07:42:23 -0800, "AndyS" wrote: Having made dozens of ham antennae over the last 40 years in configurations that probably violate the laws of physics and having had them work, I, personally, haven't found that such a difference in the antenna placement makes a hill of beans worth of REAL difference (no pun). But a lot of guys here have been doing this for 40 years also, and I'd really like to see what anyone has to say about it..... ------------ REPLY FOLLOWS ------------ If the antennas you're talking about really did work, you did not violate any laws of physics, I can assure you. :-) I operated with in-attic antennas for years and they do work surprisingly well. I earned DXCC with 100 watts and an attic dipole in a matter of a few months. Go for it. Bill, W6WRT |
#3
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I would like to hear some discussion/advice on the feasibility of
putting an antenna for, say, 30m in the attic versus on top of the roof... Here is the situation : The roof peak of my house is about 50 feet and is straight. Given the need for a dipole which is 44 feet wide, it can be mounted in either of two places: ================================================ Andy , You didn't provide the shape of your roof space eg width at loft bottom and whether there is any metal around (apart from nails/screws etc). For an HF roof space antenna I would recommend a wire loop as much as possible away from any metal and with total loop length exceeding the the length of the largest wavelenght you wish to operate on. So in your case a loop of 10m or say 35 ft would be adequate A square would be the optimum ,but a 'wide rectangular' is acceptable. Feed the loop with any balanced feeder ,twinlead electrical cable'(75 Ohms ?) or 300 -450 Ohms ribbon or 2 wires with insulator spacers. It would be best to feed the loop somewhere near the middle of a side You obviously need a balanced tuner/matching unit ,but might get away with a simple current balun Good luck Frank KN6WH / GM0CSZ |
#4
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![]() Highland Ham wrote: ================================================ Andy , You didn't provide the shape of your roof space eg width at loft bottom and whether there is any metal around (apart from nails/screws etc). For an HF roof space antenna I would recommend a wire loop as much as possible away from any metal and with total loop length exceeding the the length of the largest wavelenght you wish to operate on. So in your case a loop of 10m or say 35 ft would be adequate A square would be the optimum ,but a 'wide rectangular' is acceptable. Feed the loop with any balanced feeder ,twinlead electrical cable'(75 Ohms ?) or 300 -450 Ohms ribbon or 2 wires with insulator spacers. It would be best to feed the loop somewhere near the middle of a side You obviously need a balanced tuner/matching unit ,but might get away with a simple current balun Good luck Frank KN6WH / GM0CSZ Andy replies: Thanks for taking the time to give me your advice. However, do you have an answer or opinion about the question that I asked ? Andy W4OAH |
#5
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"AndyS" wrote in message
ups.com... 1) Just above the roof peak, straight along it, about 1 foot above. Is the ridge vent metal? Usually it is covered with shingles, but sometimes it is aluminum, sometimes plastic. I trust any foil backed insulation is in the floor of the attic rather than the roof. All other things being equal, I would expect the antenna to be noticeably better above the roof, because there will be some attenuation indoors, and greater proximity to noise makers, and things that can get overloaded by your transmitter.. But I doubt it would be a huge difference, although on wet days it may well be sigificant. If the vent is metal, then the attic antenna, because you can get it farther from the vent, may well be better. But "better" is a relative term. I suspect in 4-land you don't get the snow and ice we get up here on the tundra, but I imagine you have pretty decent storms come by once in a while. It may well be that the slight attentatuon is a small price to pay for not having to re-string the antenna every time hurricane season rolls around. ... |
#6
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![]() xpyttl wrote: Is the ridge vent metal? Usually it is covered with shingles, but sometimes it is aluminum, sometimes plastic. I trust any foil backed insulation is in the floor of the attic rather than the roof. **** Correct. All the metal is well removed. Just a wood sheathing/asphalt shingle roof.. All other things being equal, I would expect the antenna to be noticeably better above the roof, because there will be some attenuation indoors, and greater proximity to noise makers, and things that can get overloaded by your transmitter.. But I doubt it would be a huge difference, although on wet days it may well be sigificant. If the vent is metal, then the attic antenna, because you can get it farther from the vent, may well be better. **** I didn't think of the "wet days" situation..... I haven't seen much difference in antenna performance due to rain or weather tho... However, it doesn't snow here much at all. But "better" is a relative term. I suspect in 4-land you don't get the snow and ice we get up here on the tundra, but I imagine you have pretty decent storms come by once in a while. It may well be that the slight attentatuon is a small price to pay for not having to re-string the antenna every time hurricane season rolls around. **** No hurricanes in Eureka, Texas... Just tornadoes... And the antenna will usually land somewhere around where the house comes down at ..... :))))) *** The main reason for the question is my wife's opinion of acceptable adornment for the exterior of our new house...... She doesn't share my fascination with "electronical stuff" as an art form... :) Andy W4OAH in Eureka, Texas |
#7
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"AndyS" wrote in message
ps.com... *** The main reason for the question is my wife's opinion of acceptable adornment for the exterior of our new house...... She doesn't share my fascination with "electronical stuff" as an art form... Ahhh, well. That changes things. A wire antenna is practically invisible, but you wouldn't want it in the attic where it could attract lightning inside the house. ... |
#8
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![]() xpyttl wrote: Ahhh, well. That changes things. A wire antenna is practically invisible, but you wouldn't want it in the attic where it could attract lightning inside the house. .. Andy comments: Well, the difference between being "practically invisible" and being pre-emminent in grotesqueness to my wife is "practically negligible" (grin). I'm not certain that an antenna "attracts" lightning. It probably makes little difference between hitting an outside antenna, running in the feedline, and burning down the house VERSUS going thru a layer of asphalt shingles and doing the same thing...... but I can see where you're coming from..... However, in Eureka we don't usually have problems with lightning because the tornado usually blows the antenna away before the lightning strikes...... Andy W4OAH in Eureka, Texas |
#9
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AndyS wrote:
*** The main reason for the question is my wife's opinion of acceptable adornment for the exterior of our new house...... She doesn't share my fascination with "electronical stuff" as an art form... Well that settles it in my mind, do it inside the roof as high as u can get it. (use rope and pulleys so u can later play with it, when the urge hits) It should work almost as well as of it were outside and 3 foot higher. Easy to get the feel line to come away at a 90 degree angle. (not necessary, but if it does great) and last but not least It will save up your exterior adornments play with the xyl for a later project. |
#10
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![]() Sam Morgan wrote: It will save up your exterior adornments play with the xyl for a later project. Andy comments: Yeah, you would not BELIEVE the size of the television antenna we need here to get good reception (grin)........fortunately Moseley makes a good one.... :))))) Andy W4OAH |
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