Posted: 8/26/2011 7:28:55 PM EDT
| as most of you know im in a rental and am working on a 20/17/10 fan dipole. well i checked the attic and have found that there is a power wire running right down the center of the trusses. how bad will this effect my antenna and would it be bad enough that i should just forget about it? |
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as most of you know im in a rental and am working on a 20/17/10 fan dipole. well i checked the attic and have found that there is a power wire running right down the center of the trusses. how bad will this effect my antenna and would it be bad enough that i should just forget about it? Nah, the wavelengths are so long at HF it's unlikely the electrical wire would have too much/any discernable effect. Basically, don't worry abt it. The biggest problem you might have is RFI noise being coupled to your antenna from it. Think how much wiring is hidden in the ceiling just below the attic. |
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One friend has a 66' OCFD (aka "Windom") in his attic doing well for him. The 44' leg is slightly zig-zagged to fit, but he has great SWR readings.
Here's the specs on my Windom Antenna in my attic.
Final Lengths - 44' 6" & 21' 8" 40M - 2:1 SWR Bandwidth, 6.731 Mhz to 7.725 Mhz, Resonant @ 7.202 Mhz, SWR 1.1:1, 48 ohms impedance. 20M - 2:1 SWR Bandwidth, 12.78 Mhz to 14.71 Mhz, Resonant @ 14.01 Mhz, SWR 1.5:1, 63 ohms impedance. 10M - 2:1 SWR Bandwidth, 27.95 Mhz to 30.78 Mhz, Resonant @ 29.15 Mhz, SWR 1.1:1, 51 ohms impedance. 6M - 2:1 SWR Bandwidth, 50.100 Mhz to 53.420 Mhz, Resonant @ Approximately 52.00 Mhz, SWR 1.1:1. The center of 17M (18.11 Mhz) had a 7.3:1 SWR @ 18 ohms impedance. The center of 15M (21.30 Mhz) had a 6.1:1 SWR @ 150 ohms impedance. The center of 12M (24.96 Mhz) had a 6.5:1 SWR @ 11 ohms impedance. I did check 30M, it was slightly off. 2:1 SWR Bandwidth, 9.195 Mhz to 9.935 Mhz, Resonant @ 9.669 Mhz, SWR 1.8:1, 47 ohms impedance. I ended up with four bands and I don't need the tuner except for part of the 6M band. Nice antenna, thanks again! Another friend is using a coil loaded multiband dipole that I designed for him, and doing well with that in his attic. Neither report excessive noise. I'm sure both could do better with the antennas outdoors, but with HOA restrictions, they are still on the air and working the world. AFM |
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Ya never know till ya try it.
In my case the main feed goes first to the garage, then over the carport, then to the house. Shack in in the garage. I've run coax up the walls in the garage to the attic antennas. So far I've run into few problems One was mounting a 2m antenna about 6" away from a 15 amp line for the attic lights running parallel. After the dope slap I moved it a few feet away and it likes it just fine there. Other is on 40m I'm getting RF in the shack and it crashes the software when running the digital modes. Think that's more of an antenna or coax length issue than an electrical wire issue. That same 40m coax runs perpindicular with 3 feet separation from the main house feed line. Lots of juice running though those big cables. Try it. May not be a problem. |
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One friend has a 66' OCFD (aka "Windom") in his attic doing well for him. The 44' leg is slightly zig-zagged to fit, but he has great SWR readings. Here's the specs on my Windom Antenna in my attic.
Final Lengths - 44' 6" & 21' 8" 40M - 2:1 SWR Bandwidth, 6.731 Mhz to 7.725 Mhz, Resonant @ 7.202 Mhz, SWR 1.1:1, 48 ohms impedance. 20M - 2:1 SWR Bandwidth, 12.78 Mhz to 14.71 Mhz, Resonant @ 14.01 Mhz, SWR 1.5:1, 63 ohms impedance. 10M - 2:1 SWR Bandwidth, 27.95 Mhz to 30.78 Mhz, Resonant @ 29.15 Mhz, SWR 1.1:1, 51 ohms impedance. 6M - 2:1 SWR Bandwidth, 50.100 Mhz to 53.420 Mhz, Resonant @ Approximately 52.00 Mhz, SWR 1.1:1. The center of 17M (18.11 Mhz) had a 7.3:1 SWR @ 18 ohms impedance. The center of 15M (21.30 Mhz) had a 6.1:1 SWR @ 150 ohms impedance. The center of 12M (24.96 Mhz) had a 6.5:1 SWR @ 11 ohms impedance. I did check 30M, it was slightly off. 2:1 SWR Bandwidth, 9.195 Mhz to 9.935 Mhz, Resonant @ 9.669 Mhz, SWR 1.8:1, 47 ohms impedance. I ended up with four bands and I don't need the tuner except for part of the 6M band. Nice antenna, thanks again! Another friend is using a coil loaded multiband dipole that I designed for him, and doing well with that in his attic. Neither report excessive noise. I'm sure both could do better with the antennas outdoors, but with HOA restrictions, they are still on the air and working the world. AFM I just put up (yesterday) the 40m OFCD you mention zigzagged into a 50' attic. All the house wiring, including a 100a line for HVAC, is up there, from which the antenna is separated by 4-5 feet. No HF experience, but the noise floor on my radio with RG8x feedline is generally s3 or so. No contacts yet because I am a non-code knowing tech and no one seems to be on 10M, although I can hear several beacons. Can't wait for the next club meeting to grab general! |
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One friend has a 66' OCFD (aka "Windom") in his attic doing well for him. The 44' leg is slightly zig-zagged to fit, but he has great SWR readings. Here's the specs on my Windom Antenna in my attic.
Final Lengths - 44' 6" & 21' 8" 40M - 2:1 SWR Bandwidth, 6.731 Mhz to 7.725 Mhz, Resonant @ 7.202 Mhz, SWR 1.1:1, 48 ohms impedance. 20M - 2:1 SWR Bandwidth, 12.78 Mhz to 14.71 Mhz, Resonant @ 14.01 Mhz, SWR 1.5:1, 63 ohms impedance. 10M - 2:1 SWR Bandwidth, 27.95 Mhz to 30.78 Mhz, Resonant @ 29.15 Mhz, SWR 1.1:1, 51 ohms impedance. 6M - 2:1 SWR Bandwidth, 50.100 Mhz to 53.420 Mhz, Resonant @ Approximately 52.00 Mhz, SWR 1.1:1. The center of 17M (18.11 Mhz) had a 7.3:1 SWR @ 18 ohms impedance. The center of 15M (21.30 Mhz) had a 6.1:1 SWR @ 150 ohms impedance. The center of 12M (24.96 Mhz) had a 6.5:1 SWR @ 11 ohms impedance. I did check 30M, it was slightly off. 2:1 SWR Bandwidth, 9.195 Mhz to 9.935 Mhz, Resonant @ 9.669 Mhz, SWR 1.8:1, 47 ohms impedance. I ended up with four bands and I don't need the tuner except for part of the 6M band. Nice antenna, thanks again! Another friend is using a coil loaded multiband dipole that I designed for him, and doing well with that in his attic. Neither report excessive noise. I'm sure both could do better with the antennas outdoors, but with HOA restrictions, they are still on the air and working the world. AFM I just put up (yesterday) the 40m OFCD you mention zigzagged into a 50' attic. All the house wiring, including a 100a line for HVAC, is up there, from which the antenna is separated by 4-5 feet. No HF experience, but the noise floor on my radio with RG8x feedline is generally s3 or so. No contacts yet because I am a non-code knowing tech and no one seems to be on 10M, although I can hear several beacons. Can't wait for the next club meeting to grab general! More talking....less listening. Opposite of what my teachers said in my youth.  Start calling CQ on 10m. Try freqs other than 28.400, not everyone hangs out there. JA's (Japanese ops) used to hang out on 28.325.
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Exactly my experience with my setup as mentioned above.
I just put up (yesterday) the 40m OFCD you mention zigzagged into a 50' attic. All the house wiring, including a 100a line for HVAC, is up there, from which the antenna is separated by 4-5 feet. No HF experience, but the noise floor on my radio with RG8x feedline is generally s3 or so. [thread_drift] No contacts yet because I am a non-code knowing tech and no one seems to be on 10M, although I can hear several beacons. Took me a long time to figure this out on my own. "If you hear the beacons, the propagation is there." Meaning if you can hear them, there is a path to work with. Nobody on the band? False. You are on the band and quite possibly somebody else is doing the same thing. Pick a spot and call CQ. [/thread-drift] |
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Another friend is using a coil loaded multiband dipole that I designed for him.
HankEllis above is the guy. Hank, how did your antenna work out, as far as SWR, as per the sketch I sent you. Did you have to trim the antenna much, or just use the tuner? I know you've been doing a lot of PSK31 with it. |
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S3, I'd love to have only S3 noise. Usually it is about S6. How is the OCFD hearing on the lower bands? AFM It is fine on 80m, but the noise floor is a couple S units higher. I have not spent any time on 160. Been calling on 10m, but no activity. Looks like I am going to need a General CSCE. |
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S3, I'd love to have only S3 noise. Usually it is about S6. How is the OCFD hearing on the lower bands? AFM It is fine on 80m, but the noise floor is a couple S units higher. I have not spent any time on 160. Been calling on 10m, but no activity. Looks like I am going to need a General CSCE. The noise floor is higher on 80 meters naturally. Just the way it is. 
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Been calling on 10m, but no activity. Looks like I am going to need a General CSCE. Let us know when you're trying, and we can listen for ya, and/or call for you. [continuing threadjack] I'll do that but may not have much chance until this weekend. After next Thurs, I ought to have my CSCE. Have we ever attempted a 10m ARFCOM net in the technician portion of the band? Looks like 4x4ham attempted it with limited results. |
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A 10m ARFcom net will be a non-starter in my opinion. Prime example is the Feld Hell Net. Got to like the footnote. "*This net is occasional until the sunspots return Larry is looking for a NCS who can spend time at appointed time calling for checkins. This is a 10 meter net and Larry has yet to make a contact."
Have we ever attempted a 10m ARFCOM net in the technician portion of the band? Looks like 4x4ham attempted it with limited results. |
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The 40m side tuned up fine. If I recall I had to offset it another 6" to 12" to get the impedance where I wanted it. I've got full use of the band and the internal tuner in the TS-2000 handled it fine. At the time I was heavy into PSK31 but now I split my time equally between PSK31/RTTY, CW, and phone.
Another friend is using a coil loaded multiband dipole that I designed for him.
HankEllis above is the guy. Hank, how did your antenna work out, as far as SWR, as per the sketch I sent you. Did you have to trim the antenna much, or just use the tuner? I know you've been doing a lot of PSK31 with it. On 80 it was a bit trickier to get it close and ran out of time before summer hit and working in the attic became impossible. That particular design, an 80m about the length of a 20m, gave a very narrow bandwidth. 20/20 hindsight I should have gone for longer antennas. This winters project is to install a new 30/40/75 array based on the AE5JU Field Day antenna. The longer length will be easier to tune and will give wider bandwidth also. AFM, check your email inbox. 75m/80m is a tough nut to crack when you're dealing with attic antennas. You only have so much space to string the wire and it isn't near high enough to be much more than a cloud warmer. One thought that may work is to install an HF mobile antenna. A screwdriver antenna such as the Tarheel with gobs of ground radials up in the attic just might work. Route the antenna controller wiring to the shack. The bandwidth will be narrow but so what. Whatever freq you're on just adjust the antenna for it from your operating position. If you have 10 feet height in the attic it may be an option. |
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That is one of the tradeoffs with coil loading, narrower bandwidth. The 80/75 m band is already difficult to tune as just a simple dipole. You really need two dipoles, one centered on 3.900 mhz for phone, and one centered on 3.600 mhz. Some guys do both like this, wired parallel, and get the whole band easily with good SWR.
But when you shorten a dipole via coils, you do get some loss of efficiency, but shortening up to 50% you only lose about 1 db. But what you really give up is bandwidth. But this is what you must consider when you try to cram 80 meters into an attic. 
AFM |