– 2, 2003 it was described a trap filter on main wires. However,
the filter cannot be used at a high power or at super- broad bands
transmitters. One reason is that it is impossible to retune
a trap at a wide frequency range, other
reason is the trap filter does reflection of the high-frequency
energy back. So, wire to the filter can radiate also the high-
frequency energy goes to transmitter and does additional interferences.
So, in some case a trap filter can do more trouble the use.
In the case
it is possible to use an absorbing filter. Absorbing filter is
made as a coil reeled - up by a double wire (or main wire) and
placed in a metal box with a stuff that does absorbing of high-frequency
energy. Absorbing material consists of dust of soot mixed with
another stuff, as usual, with an epoxy
compound. As a rule, absorbing filters are installed as on input
of a power supply (on the main wires) as on the output of the
power supply (on the wires feeding the transmitter). Figure 1 shows a design of an absorbing filter
and places of its installation.
Absorbing filter is an active load for high frequency currents
that are distributed or from the transmitter in the main. Hence, there is no reflection of high-frequency
energy from the filter, there is no mode of standing waves on
wires going from power units, and
the time high-frequency energy will not penetrate from the transmitter
into the main, and back.
filters were made and tested by me. The coil had approximately
20 turns of the main wire. Diameter of the coil was 30 millimeters.
The coil was placed in an old coffee tinned can. The can was filled
with absorbing mix. The mix consists of a pounded coal with chalk.
The proportion was of 70 percents of coal and 30 percents of chalk.
The mix was carefully stirred in solution of paraffin with rosin,
80 percents of paraffin and 20 percents of rosin. It should get
out a compound of very rich consistence.
Then the compound was filled the can with the
coil inside. After full cooling of the compound the absorbing
filter is ready for a work.