Last year I got my home antenna up for my 2m/70cm base radio, a GP-9 mounted on a mast from my roof line.  It is working extremely well and I can reach repeaters as far as 60 miles away (I am at the 2nd highest spot in my county).  My only concern is I won't have a workable antenna if we get really severe weather and it knocks the antenna down or breaks it (the GP-9 is a long antenna with two joints).  This got me to thinking about adding a backup antenna in the attic of my home.

I measured and I have just over 11 feet (11'2") from the peak of my roof to the top of the bottom board of my roof trusses in the attic.  I was thinking about putting a GP-6 (10'2") in the attic with the tip of the antenna nearly touching the peak of the roof.  Would this be a good setup or would I be better served with a shorter antenna (with lower gain) mounted with the tip in the same place but the base higher (since the antenna is shorter)?  

Is there anything I should do or avoid doing with this type of setup?  I've never done this before so any guidance is appreciated.

I have a small "antenna farm" in my attic, Comet GP-3, home made ground plane and a 10 meter dipole, I have had no problems hitting any of the local and even not so local repeaters 40+ miles and making local contact on 10 meter (30 miles).  My GP-3 is about 1" below the peak roof beam. As always use good low-loss feed line especially the longer your run is.

Although I have a J-pole in the attic for pinging the nearby (< 5 miles) repeater my go-to antenna for 2m/70cm is a Elk log periodic. Got two. One horizontal polarization for when I putz with 2m SSB. The other is vertical poloarization for hitting the far repeaters and for 2m FM simplex. Got them both mounted on one mast and rotated by a Hy-Gain AR-35. Antenna height is around 18' from ground level.

The J-pole is to be repurposed for the APRS weather station if I ever get off my rear and get it done.

The run is about 30 feet and I'm using the left over LMR-400 from the installation of the GP-9.  In the initial install I ran the feed line from the antenna down to the basement then ran a second line from the basement up to the dining room.  I keep the radio, in an emcomm box, in the basement hooked up so it is there if we shelter from a tornado.  I can then just put a small patch cable from the antenna feed to the feed that goes upstairs and take the radio to the dining room to use upstairs when I want.  My plan is to run the second antenna feed line down to the basement as well, that way I can use either antenna from the basement, I can patch either to the dining room feed, or I can patch one to the dining room and have a radio in the basement and one in the dining room working simultaneously should I ever have a reason to do so.

My main question right now is would there be any reason to use a shorter antenna than the GP-6?  It is the longest highest gain antenna that will fit in the space I have so I was thinking it would be the way to go.  Is there any reason to think otherwise?  Normally you have a fixed mounting location so a longer antenna will increase elevation.  In this case, the top is fixed so a longer antenna lowers the mount height.  I don't know if that will reduce the advantage of the longer antenna for any reason.  The shorter antenna will be easier to manage during installation in the attic, but if the longer antenna and higher gain is worth it then I'll manage.

Go with the biggest/highest gain antenna that will fit.

The GP-6 is on the way.  

One more question, my home is brick so two ends of the attic are brick.  Basically I will have shingle and plywood on two sides and brick on two sides of the antenna once it is up.  Would it be better to run the line farther and move the antenna toward the center of the attic away from the brick to minimize interference or would it be better to keep the run as short as possible and keep the antenna only a few feet from one of the brick sides?

I finished the install last night.  I have to say, it works quite well.  I have very minimal signal or range loss when compared with the GP-9 outside in my initial testing.  In fact, it works so well I'm wondering if I shouldn't have just done this in the first place.

Nice install!  

Attic antennas can work surprisingly  well, for what they are.  Just this morning, I worked a station (SSB) On the Isle of Man, with my attic dipole, and 100 watts.  Sounds like it is working quite well for you.....have you been able to check the SWR?

I have not as I don't have access to a meter.  It would be interesting to compare the two.

ETA:  Here is the GP-9

I have a Comet GP3 and a Diamond X300A in my attic. (Along with a couple of N9TAX slim jim dual band roll up j-poles for SDRs.)

My house, although brick, has a sloping roof and the bricks only come up level with the base of the antennas.

They both have excellent SWR and forward power across the 2 meter and 70 cm bands. I figure that the attenuation

(if any) will be insignificant and the advantages of having dry, wind protected, sun protected, ice protected,

lightning protected (?), prying eye, mischivious kid protected and easy to access in all weather antennas will be a

BIG plus in the long run. Also shorter runs of coax are needed. They really get out, and hitting my favorite repeater

at 40+ miles is very easy with 5 watts out of an HT. Of course I am at 980 feet of elevation and the antennas are 40

feet off the ground which helps. They got rid of the R2 on my DStar Radios, and I am able to operate simplex to

remote stations where I couldn't do so before. So I am very happy with them. Zulu Whiskey, 73

I also have an N9TAX roll up J-Pole.  It is a great emergency backup antenna and is what I was using here at home before I got the GP-9 put up.

So far I haven't noticed much of a hindrance from the attic antenna vs the external one.  I haven't tried both side by side so to speak to see how much different they really are but the attic antenna will hit all the local repeaters easily.  I haven't gotten around to trying to hit the more distant repeaters, perhaps I'll try tonight.  The GP-9 will hit a couple just over 60 miles away, which was more than I ever expected from it.

I think some of this has to do with my location as well.  As mentioned before, I'm the 2nd highest point in the county and my basement floor is actually above the nearest roadway.  I can actually hit two repeaters about 15 miles away using an HT (FT60R) and the rubber duck antenna from my basement.  The audio isn't great on the 2m repeater but is surprisingly clear on the 70cm repeater.  If I use a patch cable and hook the HT to the GP-9 it gets amazing range for being a 5w handheld.

I was hitting a 2 meter repeater 55 miles away with one watt on my GP-3 this evening. Some noise was reported but full intelligibility and no dropouts. Line of sight is key. Now that is performance.

I also had a 20 meter contact and QSO with a native Ham on the island of Sao Miguel, Azores in the middle of the Atlantic. I love this hobby!!! I had no idea where the Azores were and was totally jazzed when I saw how tiny and isolated the place was. Fernando was his name. Only my third DX, ever. woot!