Hi Laurence sorry to hear the spruce are succumbing to the beetle. I have a
load of elm sapling at the end of my garden that suffer similarly. I think
it is worth putting the reply on the reflector as it may trigger some
violent disagreements (I hope ?) or some other ideas, and findings from
different sites.
Vertical leads for the L.
I think the reason for the suggestion of a single wire it to reduce the
capacity of the vertical to ground and to surrounding "environment"
(probably more improtant for amateur aerials). Nevertheless several amateurs
use multiple wire verticals with satisfactory results. Brian had 4 wires
originally as an open wire feeder to his 80m cage top. Mal uses three
inverted Ls in parallel I believe with the verticals connected at the feed
point. Finbar ran four lengths of vertical insulated wires together, through
a ring attached to his halyard, and then he fanned them out to form his
capacity load. It is advantageous to keep the vertical as far from grounded
items like trees, masts, and buildings. Even a couple of metres will make a
difference. There are ways of feeding a wire attached to a grounded tower
(see Rik Stobbe's tutorial on LF aerials 10 or 11, I think)
www.qsl.net/on7yd
Top-load wires
These need to be separated by at least 70cms to give increased capacitive
loading, a metre is probably better, more doesn't gain anything....put
another wire in !! The NEC "simulators" will tell you that increasing the
top load beyond a length equal to about the height of the antenna will not
gain you anything more. It is true that the extra length will not increase
the effective height or the radiation resistance (you will probably not find
received signals any stronger ) but the increase in capacity is accompanied
by an similar decrease in ground loss. Provided they are not strung over
lossy bushes, as Laurie has just discovered. I have used 1inch diam plastic
water pipe a spreaders its light and seems strong enough.
Connection or top load
Mike G3XDV discussed this with the group some while back and it does not
seem to matter whether the top-wires are in parallel or are zig-zagged
backwards and forwards The effect is the same. (I have some in parallel and
some "folded back")
If you are going to run significant power, then you will need to watch out
for areas where there are sharp bends, and also at the ends of the wire. Jim
has made some successful corona rings for the ends of his wire. I think they
are 3in diameter rings of thick copper wire, supported on the insulators and
soldered to the end of the aerial wire. Ralph has done similarly with his
SMG beacon (166.3kHz), and has quite a few pics on his web site..
I hope that helps a bit, but you will probably get plenty more ideas to
distil into a "program".
Cheers de Alan G3NYK
[email protected]
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