Frank wrote:

The following explains the construction:

http://www.g0mrf.freeserve.co.uk/variometer.htm

Variometers can be very lossy variable inductors. For proper
matching 2 elements are required.

A general rule of thumb for electrically small antennas is:
small-broadband-efficient, pick any two. One of the common features of
many small antennas is some lossy component or components which make the
bandwidth acceptable. Of course, this also means lowered efficiency,
often to an extreme extent. But most amateurs are able to measure SWR
and almost none are able to measure efficiency, so the loss fools a lot
of people into thinking the small antenna is performing well. I suspect
the variometer is the "secret ingredient" in this case, and that its
chief function is to provide loss. People duplicating the antenna might
try substituting a non-inductive resistor as a simpler way to achieve
the same result.

This isn't to say that a small inefficient antenna "doesn't work". I've
personally worked over 30 countries with a watt and a half on 40 meters
using simple antennas, and many, many people have done a great deal
better with much lower power. So you can still work a lot of stations
with a 100 watt rig and 1% efficient antenna.

Roy Lewallen, W7EL