Dear Lowfers, Medfers,

for suitabel matching  I use a transformer (See Jerry Sevicks Balun Book, "Transmission line transformers", ARRL Publications) and a loading coil with variometer, for 1,8 MHz, 136 kHz and 472 kHz. Between HF and LF I use two Vac-Relais, (Normally open contact, abt. 30 kV/10 A from Jennings), 136 k and 472k I switch with banana plugs manually.  Running to and fro for alignment of the variometers, I am using a Antenna Analyser in the shack (VA3 , Kit from Funkamateur.de) . Input resistance for 136k is about 300 Ohm, for 472 kHz abt. 60 Ohm.

Parallel to the metal marconi vertical antenna are two Fiberglas rods, 10 m and 12 m, tuned for 7 MHz and 3,5 MHz as short helix Antennas.

I do not know, if the present solution (used in three different qths) has disadsvantages for LF, that I did not realize till now.

My proposal:

- Resonant circuit in the stile of VK2AOU as base loading coil

- Or using two Helix-Antennas tuned for 472k and 136k parallel in HB9ASB-Style. How mutch the two rods must be spaced, that the electric fields are not partially shorted? Think of the influence of trees near to the antenna at 136k.

Anyway I recomend using two loading coils or two variometers with separate drives.

A not extremely cheap possibility is an electric cylinder as drive for the variometer.

http://produkt.conrad.de/45973183/elektrozylinder.htm

55, Hans-Albrecht

DK 8 ND