Cecil Moore wrote:
On Jun 4, 6:19 am, "-.-. --.-" wrote:
... how it is possible that mobile setups with the
"motorized" antennas can have a minimum of efficiency in 40 meters ?? What
the difference from a variabile motoryzed L and an ATU at the feed point ??

Most screwdrivers and bugcatchers are more center-loaded than base
loaded. The section of the antenna that supplies a good part of the
radiation is the straight section between the feedpoint and the bottom
of the loading coil. An ATU driven whip doesn't possess that high-
efficiency, high-current section. The highest current sections in an
ATU system are inside the ATU - not good for radiation. Everything
else being equal, a center-loaded antenna will beat a base-loaded
antenna by ~3-5 dB according to mobile shootout results. The radiation
resistance for a center-loaded 75m mobile antenna is approximately
double that for a base-loaded 75m mobile antenna, i.e. close to double
the efficiency.

According to 75m mobile shootout results, an ATU driven whip is ~8 dB
down from a base-loaded bugcatcher because the bugcatcher coil
radiates and an ATU is usually shielded and often uses powdered iron
toroids for the coils.

As a point of clarification, Cecil, the bottom loaded bug catcher you
refer to - is it the matching coil or the loading coil? I only knew of
mid-loaded bugcatchers.

- 73 de Mike N3LI -