Date: Fri, 07 Jan 2005 07:35:22 +0000
From: "J. Allen" <vy1ja@northwestel.net>
To: rsgb_lf_group@blacksheep.org
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Subject: LF: Antenna plans   de  J.
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Scott,

The main 137 antenna will be an inverted-L with two, 392 foot long #10 
copper clad horizontal wires fanning out from the tower in a V.  I am using 
this V-Beam antenna for reception on LF now and find that it works quite 
well.  Since I have not installed receiving loop yet, I have nothing to 
compare it to.  The receiving loop will come later.

The single-tower station at VY1JA has a tribander at 109 feet from ground. 
It is on a mast about 4 feet above the top of the tower, so the tower top is 
roughly at 105 feet.  I have forgotten exactly what the height is and could 
measure it when I work on it next, but I know that I am close and the main 
thing is getting it resonant and tuning it.

The present points of attachment of the two horizontal wires at the tower 
are at 80 feet, and the attachment points of the two end supports are at 68 
and 63.5 feet with some sag between the attachment and the ends.  I would 
say after examining this that the average heights of the two wires would be 
about 70 feet, including sag and lower end support positions.

The horizontal wires form a "V" from the top of the tower outward toward 65 
degrees and 120 degrees azimuth.  Each wire is 392 feet long.  The included 
angle in the V is therefore approximately 55 degrees.  My plans for now are 
to put a pair of 1500 Ohm inductors at the top of the tower (at right angles 
to each other) and connect one end of each inductor to one of the two V 
wires.  The ends of the V wires are insulated from the tower and at their 
far ends by power system insulators rated at 150,000 volts.

It is intended to run a #6 aluminum wire on power insulators down from the 
remaining end of each of the inductors.  At the base, it is planned to join 
the two vertical #6 feed wires, which will still need a base loading 
inductor of approximately 105 Ohms of loading for fine tuning.

The last device is the tuner, which I have not even thought about yet.... 
Once I begin construction of the amplifier, I will need to select the design 
and begin building the tuner.

Elnec shows the radiation resistance of the antenna with all resistances set 
to zero, to be about 0.02053 Ohms.  With normal resistances and without the 
tuner loss, the antenna impedance with the resistance of wire and loss 
resistance, the antenna connection impedance estimates at 7.6 Ohms.  Antenna 
efficiency (excluding the tuner) with these two 400 foot capacitance wires 
would then be about (100x0.02053/7.6)= 0.027% which I understand is good for 
an LF antenna.

Power is lost in the coils of the matching network isn't it?   I wonder how 
efficient the networks are?

500 Watts out of the rig, assuming an 75 percent efficiency through the 
tuner, = 400 Watts out of the tuner to the antenna, then (400  times 
.00027)=1.08 Watts, a close match to 1 Watt ERP, the restriction of my 
approval for these experiments.

Is the math OK?

I was planning some day to also put up a large high loop.  I can go out from 
the top of  the tower to the top of one of the 4 inch aluminum supports of 
the V ends, then using the support as one vertical loop leg, connect a wire 
at about 9 feet above ground and bring it back to the tower also at 9 feet. 
It would be an odd shaped loop (104-9)= 95 feet on the tower side and 
(68-9)=55 feet on the support side, with top and bottom wires which  will be 
about 405 feet long, each, (longer than the V legs because there are no 
insulators involved and no support wires.

Why I say that I WAS planning to put up the loop is that the efficiency of 
the loop checks out to be about 1/10 as good as the inverted-L. I have no 
trees nearby, there is no advantage to the loop which I can see, except 
possibly its directivity.

These are my antenna plans for the warmer weather.  Feedback?.

Does this give you an understanding of my antenna plans?  If you need 
anything else explained further, please ask.

J.
VY1JA