Topband: First Top Band Antenna

[George (K8GG) & Marijke Guerin]

John Cowan wrote:
----- Original Message ----- 
From: "John Cowan" <w0tmm at yahoo.com>
To: <topband at 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