-----Original Message-----
From: Eugene Colton
Sent: Monday, September 03, 2018 12:25 PM
To: donovanf@starpower.net
Cc: topband@contesting.com ; MU 4CX250B
Subject: Re: Topband: Air wound coil
Jim,
@ say, 1.83 MHz, the electrical length of your vertical is about 47.4 deg,
necessitating a top hat of about 42.6 deg. I followed the prescription of
John, ON4UN and calculated out a surge impedance of 377 ohms based on an
average radiator diameter of 2.25 inches; the hat capacitance would be
about 212 pf. If you did a disc cap hat, it would need to be maybe 6m
diameter, pretty big. If you just used T-wire loading you need maybe 35m
of top hat.
Not sure how you would use this antenna on 80m.<<<
***
Install a trap below the top hat wires.
I have an approximately 21 m tall radiator with three top hat wires to
resonate on 1825 kHz.
Just below the top hat wires is a trap consisting of a coil of aluminium
tubing and doorknob capacitors resonated around 3600 kHz.
On 160 m I use an L-match network.
On 80 CW I switch out the capacitor and use the series inductance of the
L-match.
On the DX Window, I bypass the network and feed the radiator directly. It is
resonant above 3800 kHz, where I cannot transmit, but it is quite ok for
just below 3800 kHz.
It is all controlled by a toggle switch at the operating position, with two
relays in the feed point matching box.
Later this spring, this is coming down, as the telescopic aluminium mast
joints are causing me grief with corrosion and intermittent conductivity. Up
will go a wind up telescopic mast supporting continuous wires from feed to
top hat.
I am enjoying the exchange of information on this thread. Keep it up!
73,
Luke VK3HJ
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