Co-located 2M and 6M vertical dipoles - Issues?

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Co-located 2M and 6M vertical dipoles - Issues?	Reply
by KI6FZC on October 20, 2009	Mail this to a friend!
My apartment manager has graciously allowed me to put ham antennas on the roof of my building! There is a 4-in. pipe, securely mounted to the structural concrete, rising about 15 ft. over a 4 story building, so I am optimistic. To keep things simple, I was thinking about vertical dipoles, 2M over the 6M. Any comments or recommendations would be appreciated, but I am especially concerned about: (1) how much vertical separation is needed between the two dipoles, (2) how much stand-off from the antennas needs to be manintained for the coax feedline, (3) can I feed both antennas from the same feedline, as both systems will never be used simultaneously, and (4) if (3) is yes, should I use a coax splitter, or will simple point-to-point conections (TX to 6M-centers to 2M-centers) be adequate? Thanks.

RE: Co-located 2M and 6M vertical dipoles - Issues?	Reply
by KQ6Q on October 20, 2009	Mail this to a friend!
A Diplexer would be better - splitter that would direct energy to the specific antenna. I use one to have a single run of coax feeding 6m and 2m beams - the end in the house has an A-B switch. Or you could use a discone ($60 from radio shack) which would support both bands with one feedline. Also the discone will work for 220, 440, 900, and 1296 if you choose! (I use my for occasional 440 and 1296 in VHF contests, but it will hit repeaters just fine). Fred , KQ6Q

RE: Co-located 2M and 6M vertical dipoles - Issues	Reply
by KM3F on October 20, 2009	Mail this to a friend!
IMO what you see as a simple antenna solution is not so simple in actual practice. Why not go for a 6 and 2m regular vertical with it's factory radials and have it over with and a better working antenna with a single feed line that doesnot get into the antennas radiation field. Look at GAP, Comet, etc. On 6m you can work DX with a vertical when ES is in otherwise it's FM repeaters or locals and mobile. 2M will be repeaters only for the most part and simplex with other locals. If SSB is intended on both bands, you need horizontal beams with rotors.

RE: Co-located 2M and 6M vertical dipoles - Issues	Reply
by VE3NEAR on October 22, 2009	Mail this to a friend!
Gp-15 from Comet would be your answer. Unless you have parts, and are on a tight budget. or... if you require a different radiation pattern.

RE: Co-located 2M and 6M vertical dipoles - Issues?	Reply
by WX7G on October 23, 2009	Mail this to a friend!
You want to build an antenna system for 6 and 2 meters that is vertically polarized and uses one coaxial feedline. One solution is to feed a 6 meter dipole and have a parasitically coupled 2 meter dipole. Using 1/2" tubing the 6 meter dipole is 8.8'. The 2 meter dipole is 3.2' and is spaced 2" away. A simulation shows no problem with the feedline being routed at a right angle to the dipole for 3' and then routed downward. Closer than this and the feedline shield current increases the pattern suffers. It looks good with or without a balun. If you build it can you report back with your findings?

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