It is possible to use coaxial cable with any wave impedance- 50 or 75
Ohm. Matching impedance of the 4:1 transformer depends on the
coaxial cable. At 50- Ohm cable it is got transformer 200:50-
Ohm, at 75- Ohm cable it is got transformer 300:75- Ohm. Transformer
300:75- Ohm should have best matching result with open line transformer.
There are lots link in the internet how the transformer may be
calculated. One of them is:
When the coaxial cable symmetrical transformer is used the broadband
of the antenna depends on the broadband of the transformer. As
usual coaxial cable transformer has good matching at the 5% frequencies
band calculated from the central working frequency of the transformer.
So, when such transformer is used the broad band of the Rhombic
Antenna is limited to pass band of the transformer.
Antenna may be made from a strand wire in diameter 2- 3- mm. It may be
copper, aluminum or bimetal (with copper or aluminum layer) wire.
Terminated resistor at the antenna may be any small power non-inductive resistor. This one should be protected from atmospheric