I am currently trying out a horizontal loop on my roof. I live in the trop
floor flat and have a 21' x 24' rectangular flat roof with a 3' parapet (low
wall) around. The roof is some 30' above ground.

I have draped a 21' X 24' loop of wire aroiund this parapet and fed to the
tuner with just 6' of 600 ohm ladder line. The tuner is an SGC SG-230 laid
on the roof and has its feed cable (combined coax/control/power cable)
wound as a choke balun. The tuner is effectively acting as a balanced
drive.

Results so far.
1. The natural resonance is a little below 40M
2. I can match on all bands from 160M to 10M.
3. It is definitely acting as an NVIS on the LF bands.
4. It works better on LF at night. This could be due to the radiation going
upwards and ionosphere reflects LF at night.
5. It acts like an inductive loop pick up for any QRM amanating from the
house.
6. Efficiency is generally low. Lobes are all over the place on the HF
bands.

I will try and raise the loop a foot or two above the parapet tomorrow and
see if this helps. Otherwise I am not impressed!
I used to get better results with a 30' vertical wire on a fibreglass
fishing pole. Unfortunately I don't hasve a good ground for a vertical here
and the vertical would cause problems with the local planning authorities.

If I can't find a way of making it work better on 80M and 40M I will
probably resort to a very short loaded dipole diagonally across the roof.

Richard (Dick) G4BBH