Date: Mon, 18 Dec 2006 14:40:32 -0800 (PST)
From: Vojtech Ritzko <om8aw@yahoo.com>
Subject: Small vertical RX 4SQ-Detuning the unwanted vertical structure
To: topband@contesting.com
I am just finishing the home made project.
RX 4SQ for 160m consisting from 4-11m high
verticals loaded to 75 Ohms on 1.83MHz
and cross fired with 0,160,160,320
degrees...........on very critical footprint 10.6x10.6 meters .
1/16 spacing is the only solution to overcome lack of space.
The expected output will be around -30dBi
so IK4AUY(2x 2N5109) PREAMP will be used to improve the gain..............
Unfortunately the lack of space is not the only problem.
I have old candelabrum which is 15m tall (steel
mast equipped with lamp) in very close vicinity (just 2.5m from one element).
In tried to detune the candelabrum structure electrically.
I connected the shunt feed arm on 15m candelabrum
at 10m height and dropped down the shunt feed wire.
I measured impedance = 0.5 +j200 at 1.83 with
network analyzer connected in series against the ground.
(Ground connected to 4 SQ radial array .Each
vertical is armed with 16 x 10m long radials to avoid impedance variation)
Next I connected the ?j200 capacitor (435pF) instead of network analyzer.
Is there any optimal ratio between the height of
support which I like to make electrically invisible
and height of the shunt feed arm connection???
I now just 3/16 wavelength rule for very high structures??????.
TNX
OM8AW
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