Message-ID: <003d01c07e54$877c5940$c507883e@default>
From: "MAL HAMILTON" <MAL@g3kev.freeserve.co.uk>
To: "rsgb" <rsgb_lf_group@blacksheep.org>
Subject: LF: Loading Coils
Date: Sun, 14 Jan 2001 17:04:02 -0000
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Hi Dave
Sorry to hear about your misfortune and I hope you get it all going again
soon.
The correct place for antenna loading coils are directly beneath the
vertical drop wire of the vertical if it is base loaded, or hanging
vertically if centre loaded.
During the early 1960 period there was a debate going on about where to
locate the loading coil for 160m on short vertical fixed antennas and mobile
installations.
The consensus of opinions after testing was NOT to screen the base loading
coils because they contributed to the radiation of the signal. This was also
the case on 160m mobiles. Those with the loading coils in the boot/trunk of
the car and screened radiated a weaker signal than those with the base
loaded coil exposed at the base of the normally 8 feet vertical. Field
strength tests at rallies confirmed this given that those tested were
running the same rf power.
Any vertical that I have ever used for MF or LF that needed a base loaded
coil had it positioned vertically at the bottom of the vertical wire drop
and this works very efficiently, any derivation from this degrades the
radiation efficiency of the system.
Locking loading coils up in farady cages is bad procedure on 73/136 khz with
the power levels we are using. It was also found that long narrow loading
coils positioned vertically at the base of the vertical and not screened,
radiated more efficiently than SQUARE coils.
I expect the long narrow loading coil acted like a continuation of the
vertical getting more like a helical wound vertical.
Wind you coils with teflon insulated 2.5mm or larger wire, get them outside
at the base of the vertical in the rain, snow, frost, wind etc to keep them
cool and you will not have any problems.
G3KEV