I've ran various dipoles cut for many different bands in my attic.
An indoor antenna should always be a last resort and not chosen over an outdoor antenna if you can helpt it.
Some things that will effect indoor antennas:
1. Construction materials of the house - aluminum siding, metal roof, metal anything - bad.
2. Wiring in the attic will cause coupling and you may have to spend extra time pruning it for lowest SWR if fed with coax.
3. The height above ground of your attic. For 11 meter 9-18 feet and above is best...my attic is about 25 feet off the ground and the 11 meter dipole has a very predictable bi-directional radiation pattern. (the dipole is directive off the broadsides at heights of a 1/4 wave and greater.)
how well does it work? assuming that you are at a good hieght above ground they work pretty well.
how much power? Since it is in an attic I wouldn't dump more than 200 watts in it...probably 150 max...but depending upon your attic and if you have it suspended some how you may feel comfortable with more. something else to consider is the max power handling of the feedline that you feed it with.
how big is it? the equation is 468/frequency so for channel 20 CB the equation would be
468/27.205=17.2
You most likely will have to prune it for lowest SWR after you cut the first length. if you are cutting it for a freq range then you may want to find the lengths for each end and then average them.
What's the best configuration for local? Well since we are talking about an attic, I guess the only way you can put it is horizontal. If you could put it in an inverted V config then the radiation pattern would be more omnidirecitonal.
Something you could do is install 2 horizontal dipoles and place them in a cross. This will help cover any nulls you may encounter. However, you may not have any nulls if you are very low to the ground and this may not be needed. This may also help you figure out which direction you like the best and you can take one out if you want.
is the double bazooka the best? There is some talk about this...I have never used one but what I understand about them is that they provide a low SWR over a wide freq range but their radiation pattern also changes as you move away from the design freq. This is not a great concern though if this is your only option and you are not all that worried with radiation patterns.
I use #12 AWG wire for my dipoles and short runs of coax or ladder line. If I want more coverage I just 'tune' with an antenna tuner. With short runs of coax feedline loss is not that great and with ladder line it is virtually lossless.
hope this helps.
