Need help with an attic antenna

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Need help with an attic antenna

Postby AMK0123 » Mon Aug 02, 2010 10:54 am

Hope someone can help me out here. I recently got a Spider base scanner antenna as a gift. I wanted to put in on the roof but that wasn't going over to well with the wife and it says that you can put them in the attic so last evening I mounted the antenna to one of the cross beams in my attic and the reception is terrible. I have a Bearcat base scanner that I have had near a windows and it picks up rather well. Living in central Dutchess county I usually have no problem listening to the Hudson and River lines from Newburgh / Beacon up through Poughkeepsie including the Roseton detector on the river line. Now I can't pick up the detector and most of the train talk I can hear is static at best. I read on other sites about wrapping wire around the base of the antenna and laying them out across the floor of the attic. I even though maybe to wrap it around my chimney pipe for my oil burner. Don't know if these ideas are good or crazy! Any help would be appreciated. The actual antenna is the one I have listed below.
http://www.scannerworld.com/content/pro ... l/SP800BNC
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Re: Need help with an attic antenna

Postby Ken W2KB » Mon Aug 02, 2010 12:10 pm

AMK0123 wrote:Hope someone can help me out here. I recently got a Spider base scanner antenna as a gift. I wanted to put in on the roof but that wasn't going over to well with the wife and it says that you can put them in the attic so last evening I mounted the antenna to one of the cross beams in my attic and the reception is terrible. I have a Bearcat base scanner that I have had near a windows and it picks up rather well. Living in central Dutchess county I usually have no problem listening to the Hudson and River lines from Newburgh / Beacon up through Poughkeepsie including the Roseton detector on the river line. Now I can't pick up the detector and most of the train talk I can hear is static at best. I read on other sites about wrapping wire around the base of the antenna and laying them out across the floor of the attic. I even though maybe to wrap it around my chimney pipe for my oil burner. Don't know if these ideas are good or crazy! Any help would be appreciated. The actual antenna is the one I have listed below.
http://www.scannerworld.com/content/pro ... l/SP800BNC


It looks from the photo that the downward pointing elements might form a groundplane and adding any additional wires would not be of benefit. If not the groundplane, for railroad frequencies, the length of wires needed would be approximately 17 or 18 inches long. Longer than that would not make any noticeable difference at railroad frequencies.

That said, does the attic have any foil insulation at or above the level of the antenna? Does the end of the attic have aluminum siding at or above the level of the antenna? Is there possible an underlayment of metal foil or sheet under the roof shingles? If any of these are true, the antenna might be shielded, at least in some directions. Even the wood of the attic will cause some attenuation, but anything metallic would definitely attenuate the signal significantly.

The other possibility is that the coax is not making a good connection or is shorted. How well does the antenna perform with the coax at the window, or outdoors? (temporary check)
~Ken :: Fairmont ex-UP/MP C436 MT-14M1 :: Cessna 177B Cardinal N16019
Black River Railroad Historical Trust :: My Personal Site
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Re: Need help with an attic antenna

Postby CarterB » Mon Aug 02, 2010 12:14 pm

If attic has a window, mount closer to that. If not....probably better to mount centrally to a floor joist rather than to a roof beam. If roof is pitched and no metal flashing, should work..not as well as outside, but still should get signal. Wrapping any wires or anything of the sort will make things worse, not better. To try out reception, hang the thing outside and hook it up to test. If it's scratchy outside then it's gonna be worse in attic. If fine outside, move it around to locations in attic to get best possible reception.
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Re: Need help with an attic antenna

Postby AMK0123 » Tue Aug 03, 2010 8:08 am

Thank you both for your quick responses. Today I'll bring the antenna down and check it outside and if all goes well I'll remount it on one of the floor joists in the center of the attic. Attic is pitched with about a four foot height in the center, plywood with tar paper and asphalt shingles. Hopefully it works! I'll keep you posted.
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Re: Need help with an attic antenna

Postby Steve W » Tue Aug 03, 2010 12:23 pm

Are you using the proper coax? check your lines with an ohm meter to see if the cable is open or shorted
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Re: Need help with an attic antenna

Postby CarterB » Tue Aug 03, 2010 12:55 pm

Good point, Steve. Should use RG8 coax if over 100ft or RG8 100ft or less. The RG8 will have less db loss no matter what.
Also proper types of N connectors, (male or female) and cable properly trimmed back with good coax tool and properly crimped connectors.
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Re: Need help with an attic antenna

Postby Steve W » Wed Aug 04, 2010 8:03 am

I doubt there will be N connectors, maybe PL259/SO239 but unless he is using a "real" radio it would be a BNC or if it is a MOTO it would be a mini uhf
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Re: Need help with an attic antenna

Postby AMK0123 » Thu Aug 05, 2010 9:11 am

Thanks for all the replies. Not sure the type of coax cable / but it "say's" low loss cable. It did come with a BNC connector. I've tried moving it around to several different locations in my attic with no luck. Will keep trying but it looks like I might have to stick to the basic antenna that came with the Uniden scanner that affixes to the back and leave the unit by the window....
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Re: Need help with an attic antenna

Postby Ken W2KB » Thu Aug 05, 2010 9:56 am

AMK0123 wrote:Thanks for all the replies. Not sure the type of coax cable / but it "say's" low loss cable. It did come with a BNC connector. I've tried moving it around to several different locations in my attic with no luck. Will keep trying but it looks like I might have to stick to the basic antenna that came with the Uniden scanner that affixes to the back and leave the unit by the window....


RG8 coax is about 1/2 inch thick and RG58 about 1/4 inch. Both come in varieties with differing center wire (solid or stranded), shield (percentage shielded) and dielectric type (the insulator between center and braid). Some of both types are low(er) loss than their brethren of the same size, but the RG8 will always be less loss than the RG58.

Did you check your cable for a short circuit between the center conductor and shield braid? And check for continuity of both the center conductor and shield braid? Failing either test would result in low signal strength.

What about temporarily mounting it outdoors for a test?
~Ken :: Fairmont ex-UP/MP C436 MT-14M1 :: Cessna 177B Cardinal N16019
Black River Railroad Historical Trust :: My Personal Site
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