Doc Gruis schrieb:
This following episode was told to me by an old time BC engineer about
an early station located in the state of South Dakota.
It was not at all unusual for stations, studios, anyhow, to be located
on the top floor of some building. It was not so common for the
transmitter to be there as well. But in this case, that is where the
transmitter was indeed situated, perched proudly above the highest
prominence on the roof of this particular hotel.
The testing of the station went very well. It was in the middle of the
night.
But on the day of the official sign-on, and there were several
dignitaries there, it was impossible to keep the station on the air
because it was impossible to keep the antenna tower in tune.
It had been mounted on the top of the elevator (hoist) shaft! And as
the greeting crowd and other business started for the day the elevator
acted like a very large tuning slug!
This reminds me of a problem I had encountered when still living in Munich, with
much restricted space for antennas. For all HF bands I just had a 21 meters
end-fed wire available, with a wire counterpoise in the loft, also connected to
the house ground and the TV antenna mast.
On 160 meters I had to employ base loading, but I wondered that the VSWR often
was higher than normal, until I discovered that optimum VSWR depended on how
many apparatus I had connected to the mains in my shack (which had been just
below the loft), thus varying the number of radials for 160 meters!
To cure this problem, I had to insulate the counterpoise from the house ground
and TV-mast for RF, using a big toroid choke, and to feed the antenna for 160
meters via a 1:1 separation transformer. Now the 160 meter antenna may have
looked like an asymmetrical dipole, but the tuned section had to use the
insulated counterpoise only as the other antenna end. Tuning of the antenna now
had been entirely different from the previous setup, but the mains wires
remained neutral.
/3 Ha-Jo, DJ1ZB
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