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Hi,
JB, LF,
Try
and keep the top loading wires at least 4-6 feet away from the support towers,
and make sure that the wires are taut and don't sway about in the breeze. You
will find that the antenna is sharply tuned, and the tuning will vary as the
wind blows! This also applies to bits of the antenna that you would think would
be at the same potential, e.g. parellel multiple wire feed
lines.
If you
want to increase the top-loading capacity...always a good thing... you can join
the ends of the "legs" of the Y with further wires. This will allow you to
reduce the size of the tuning coil and reduce your losses.
If you
do intend to transmit with this antenna, pay attention to the way you terminate
the ends of the top wires. Try to avoid sharp points, and end the wires in loops
to reduce corona effects. I get significant corona running 200W RF into a Tee
with a 60m top, and it only gets worse as you turn up the wick. This can cause
TVI...well it does for me!
Lastly, if you are using a tuned loop nearby to receive, you will find
that the vertical will play havoc with the polar diagram of the loop if it
is tuned to the same frequency. I get round this by using a relay to open the
earthy end of the coil when the vertical isn't in use.
I'm
not sure what the VE licensing regulations allow, but it can be fun to just put
a couple of watts of RF into the antenna, to see how the whole thing tunes up.
You don't need much, just 4 or 5 watts from an "audio" amp on 137 kHz is all you
need. I can recommend Jim M0BMU's phase meter as a really useful means of
detecting if your antenna is on tune, and you can watch the phase swing
around when the wind blows!
73,
Dave G3WCB IO91RM
Hello Alan, Jay, Warren, et all,
Thanks for your replies to my question concerning
a "T" antenna.
As you had suggested, I plan to use Dacron rope
between the
end insulators and the towers. The
insulators are commercial
ones that I "liberated" from a ship's HF antenna, so they should
be fine for my application. I do intend to
transmit at some time
in the future, but for now the antenna
will be used for receiving.
The top loading will be three wires, one from
each of the towers,
converging at a common point midway between them,
which by
luck is also over a naturally wet area
of my property. There will
be a total length of 190 feet of horizontal top
loading, the ends
being slightly higher than the central common
point.
I plan on using a multiple rod grounding system at the feed point,
along with tieing into the # 8 bonding ground wires
interconnecting
the three towers. Those bonding wires also
connect to the mains
grounds at both my house and the shop, about 100
feet apart, so
I'm confident that I've got a pretty good ground
system.
73, J.B., VE3EAR - VE3WZL
Solar and wind
powered
EN93dr
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