[HCDX] Antenna direction switched by wind

["Karel Honzik" <karel-honzik@xxxxxxxx>]

Hi,
this is an interesting story of my long wire antenna contra strong wind.

This winter I found out that during strong wind (not often, ca. once per
month) I hear strange crackels (and something more, read on) comming from my
antenna. The antenna is a 80 meters long wire on a roof of our
multi-apartment building. Direction: East-West. On the roof the antenna is
connected via balun to a coax cable which goes down into my flat in the 5th
floor of this 8-floor house.

During the crackles I found out that on medium waves, on the same frequency,
I hear one station at one moment and another station a few seconds later -
like somebody is switching the antenna direction for me...

While tuning accross the MW band, I found certain channels where the
phenomenon was the most expressive.
It was like the antenna direction being switched between two positions (A,
B) and I could hear the following stations on these channels:

738 kHz
A:  Spain (SW) = south-west
B:  Israel (SE)

1080 kHz
A:  Poland (NE)
B:  Iran (E)

1179 kHz
A:  Sweden (N)
B:  Roumania (SEE)

1215 kHz
A:  Russia/Kaliningrad (NNE)
B:  Great Britain (W)

You can see clearly that in the A position there are stations from northern
or southern directions, while in the B position there are stations from
western or eastern directions.

The strength of the stations changes dramatically, it can be even 30 dB. I
thought - in the beginning - that the wire was broken and the strength
simply fluctuated but than I found out that it was not the case.

One example:
738 kHz: Spain and Israel change their signals on the frequency, once Spain
is S9+20, then it goes down within a second to almost inaudible and Israel
jumps in also strong - S9+.
At the same moment, Dutch station on 747 kHz has permanent signal, not
influenced by anything, you can hear only crackles.

Before I get on the roof (now it is quite dangerous because of ice from
melting snow freezing again during the night) I just wanted to share this
interesting story with you. Maybe somebody knows what is behind this
unpleasant (and interesting too) phenomenon.

Note: looking up from the street the antenna position seems to be unchanged,
it is still fixed between two supporting points, ca. 2 meters above the
roof.

GOOD DX,

Karel Honzik
the Czech Republic (Czechia)
***********************************
AOR AR-7030
80 m Long Wire

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