The phenomenon, hysteresis at a coaxial cable, was opened randomly. What
is the phenomenon?
We know, when a coaxial cable hangs for a long
time at an opened air, losses of the coaxial cable start to increase.
For HF- ranges it does not matter, but at VHF ranges the signal
starts to fade. However, at those times a SWR in the coaxial cable
is not aggravated, and on the contrary, a SWR even is improving.
It is obviously the reflected wave cannot reach to the SWR meter
because the wave faded in the losses coaxial cable. But a transceiver
cannot catch far radio signals.
Such matter was with me, when one service VHF- radio, that was served
by me begun to work not properly. I found, that the coaxial cable
weaken radio signal more the 10 dB. I just metered the power at
the transmitter output, it were 10 Watts,
and at end of the coax feedline, it were 2.8 Watts. Then I tried
to remove the bad coaxial cable from a cable shaft, but I could
not remove the cable, although I very vigorously shook the cable.
So, I could not remove the cable, and I connected the old cable to the
transmitter and decided to go
for help. But, before that I tried
the transmitter in the air. It impossible, but far radio station
heard me! I again metered the power at antenna terminal of the
coaxial cable. It was 8 Watts. So, the losses drop from 10 to
2 dB. I cannot explain the phenomenon, I only observed and used it.
I proved the phenomenon in practically way. For this purpose, losses
at old coaxial cables, that were enough long time laying
in crude places or hanging on opened air, were measured on frequency
of 144 MHz. Then the coaxial cables had been vigorous shook and
tapped by a wooden hammer. Well, losses in the coaxial cables
dropped on to 2- 6 dB.
I have mentioned, at coaxial cables
with polyethylene insulator that are at an opened air the phenomenon
is observed usually in the middle of winter or in the end of spring.
Do you have any idea about it?
It allows me to recommend, for decreasing losses at hanged at an opened
air coaxial cables, time to time to shake up the coaxial cables.
Before usage of old coaxial cables for construction of feeder
systems, the coaxial cables must be vigorously shook and tapped
at all of the length by a wooden hammer.