Should I "hang" the ladder line down about 3" from the floor joists?
That should work. I've run it through the attic and the crawlspace under the house
before with no problems.
Also should I put twists in it as it passes near HVAC ducts?
Cross them at right angles. Twists aren't necessary unless you are running parallel
to another conductor of some sort, but they don't hurt.
Should this type of installation even be tried or just use coax and a balun of some type at some place before the antenna? And if so where and what type of change over from unbalanced to balanced is the most efficient?
The most efficient point is either at the tuner, or at a point where the SWR on the coax
If you are using ladder line because it has low loss, then going through a remote balun with coax
from into the house to the tuner, you may find that the loss in that short length of coax is higher
than if you ran coax all the way to the antenna, because it is operating at a high SWR. In fact,
the losses in 15' of RG-213 used that way can be twice as high as running 75' of RG-58 to the
antenna, and that doesn't include possible tuner losses (which are often, but not always, fairly
low.) If the ladder line is an electrical half wavelength (or multiple thereof) on each band, it
may work fine. If it is a quarter wave (or odd multiple) on some bands, and the antenna is
50 ohms, you can have a very high SWR on the coax. The impedance that the coax sees
is a function of the antenna, the ladder line length, and the operating frequency.
You're building a fan dipole
. Usually that is done to provide a low SWR with coax feed
across multiple bands, so no tuner is needed. Unless you have a very lossy feedline, there
usually isn't much benefit to using ladder line in that situation. On the other hand, using
ladder line allows you to operate multiple bands on a single doublet. For example, a 20m
dipole can be used on 20m through 10m, and possibly on 30m or 6m. (You do have to
watch the radiation patterns when covering more than a 2 : 1 range.)
There may be some specific reason why you are using a fan dipole with ladder line feed,
but it isn't common. Usually multiple dipoles on a common feedpoint are used with coax
feed, and ladder line is used for a single wire used on multiple bands. Not that other
combinations won't work, but it is good to be clear why you're choosing that particular