The antenna was installed across wooden window frame. Perimeter of the
loop in my case was 4.7- meter. Antenna could be tuned from 14
to 30- MHz. I fed the antenna 50- Ohm coaxial cable. However,
also I used to 75- Ohm coaxial cable with success. Figure 1 shows the antenna. At antenna
feeding terminal a simple home- brew symmetrical device (several
turns coaxial cable coiled on to big ferrite ring) was installed.
Loop was made from wire in 0.3- mm (28- AWG) diameter. Wire was attached
to the window frame by scotch. Variable capacitor should be with
big gap between plates. However it is depends on power. I used
usual capacitor 12- 495- pF from old tube receiver when I run
30- Wtts at 14- MHz and 10- Wtts at 21 and 28- MHz. My antenna
was installed at 4th- floor at 5- store concrete building. Window
was at North- East side. While a short time at 20- meter band
there were made QSOs with 36- countries. There were ex-USSR, USA,
Canada, Japan, Europe, Asia. I worked by CW (50%), SSB (40%),
and then RTTY and SSTV.
The window loop antenna may be installed practically at any window frame.
Frequency range the loop antenna depends on perimeter of the loop.
Small loop would be tuned to high bands loop with long perimeter
would be work at lower bands.