"Richard Fry" schreef in bericht
...
Various types of "anti-fade" radiators are used by many of the 50kW
stations
to try to minimize this effect.

There is a tradeoff in the electrical height of the usual AM broadcast
transmit antenna between producing the greatest groundwave and generating
an
excessive high angle skywave that can interfere with that groundwave at
night.

A 225 degree vertical is about optimum for groundwave, but has a high
angle
lobe that can cause this type of interference problem. A 195 degree
vertical has less groundwave but little/no high angle lobe, and so is used
by many full time 50kW stations. WJR, Detroit is an example of a station
using a 195 degree vertical (700 foot guyed tower).

Other antenna types also have been used for this, such as the "Franklin,"
which is a sectionalized antenna with one vertical radiator above another,
each driven separately.


Have a look at this:
http://www.waniewski.de/id35.htm

The text is in German, but the diagrams and photos show an aerial system
with its feed at 90 meters above ground level, to reduce skywave.
You can click through several pages at the top (1-15).

gr, hwh