John Cowan wrote:
----- Original Message -----
From: "John Cowan" <w0tmm@yahoo.com>
To: <topband@contesting.com>
Sent: Tuesday, July 11, 2006 9:58 PM
Subject: Topband: First Top Band Antenna
...snip....
> As for the antenna it will be an inverted L. I have another structure 130'
> away to attach the end to. Based upon the materials available I plan on
> the vertical wire being 8' from the tower. The horizontal wire will have
> to slope down about 18'.
Sloping down is not a problem in my opinion.
> I would like opinions on whether to place a trap at the top so I could use
> it on 80 meters as well ad 160 meters?
>
In my opinion an 80 meter trap is easy to install and well worth it. A
couple of hints:
The trap will need about 200 pfd of capacity. Make it up of 2 or more
ceramic "door knob" capacitors, such as 2 x 100 pfd or 3 x 75 pfd or 4 x 50
pfd. The current cannot be easily handled by a single capacitor. (I blew
up a 200 pfd 20KV door knob with a KW).
One of the best coil forms is gray UV resistant PVC pipe or conduit. I
suggest 2 inch (2.375" OD) or 2-1/2 inch (2.875" OD) and 10 gauge enamelled
copper wire spaced about 4 turns per inch.
The trap will have enough inductance on 160 to shorten the overall length
about 15 feet/5 meters.
Also, the 80 meter feed point impedance will be at 36 or more ohms, so using
an UnUn for 160 will require a switch to remove it or change the tap for 80.
73 George K8GG
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