Use of fishrod antennas is getting more and more common to cover all bands 7 ...
28 MHz, including WARC. The typical length of the radiating wire is about 25
feet, that is about one quarter wavelength at 10 MHz.

On lower frequencies (e.g. 7 MHz) that antenna shows a low radiation resistance
and a strong capacitive reactance. On higher frequencies resistance goes up and
down with frequency, showing very high peaks, and reactance does the same,
though obviously with a different pattern.

Typical configuration used is:
- 1:4 transformer (balun or unun) at the antenna
- 300-ohm or 450-ohm flat twin-lead
- tuner at the transmitter

SWR is generally high, except on certain specific frequencies (which may not
fall in the amateur bands).

I would like to hear some opinions on the usefulness of using the transformer
and the twin-lead. My arguments a

- above 10 MHz, where impedance is generally fairly high, the transformer could
(??) be helpful to reduce SWR, but below 10 MHz it should be harmful, as its
transformation goes on the wrong side.

- use of the twin-lead is usually justified by its low attenuation, that limits
the extra attenuation caused by the high SWR existing on the line. In my opinion
the 300-ohm twin-lead attenuation is reported to be low mainly because it is
measured in presence of a 300-ohm load, that draws low RF current. But in the
subject application, where the antenna impedance is uncontrolled, what should
count is the ohmic resistance of the twin-lead conductors which is not
particularly low due to their fairly small diameter. Wouldn't an RG-213 do
better than the twin-lead?

Thanks for your comments & 73

Tony I0JX
Rome, Italy