Description and pictures of the Indoor Antenna for
the 20 Meter were published at ham forum at www.cqham.ru . Author of the antenna is unknown to me. However the antenna is work
and may be used in tight conditions.
Antenna may be made practically from wire having any
reasonable diameter – 0.5- 2.0- mm ((24- 12 AWG). Inductors wound
on a plastic form in 25- mm diameter and length of 60- mm (may
be used pieces from plastic water tube) by wire in 0.5- mm diameter.
In the center of the antenna placed RF socket S0-239. This socket
installed inside small plastic box. Antenna may be feed by 50-
Ohm coaxial cable. It would be very useful to place RF choke (or
balun 1:1) near feed point of the antenna.
It maybe 5- 10 ferrite ring or several ferrite clips on the coaxial
cable. Antenna may be tuned to resonance by side length of wires.
Theoretically (in free space) such antenna has low
input impedance (near 10 Ohm) and narrow bandwidth. However my
experience shows that inside a room where there is lots of RF
lossy objects such antenna may have
input impedance close to 50- Ohm and 200- 500 kHz bandwidth at
1.5:1 SWR in the band.