Topband: T Vertical feed

[Jim Brown]

On 1/26/2012 9:10 AM, Paul Christensen wrote:
> Based on your description, I just ran your "T" in 4Nec2 with the NEC/4.2
> engine.  Your T should have a base Z near 21+j110 at 1825 kHz and will be resonant at 1620 kHz

The relatively high VSWR of this impedance can be VERY easily converted 
to 2:1 by simply adding a series capacitance equal to 110 ohms at 1825 
kHz. This brings the drive point Z to 25 ohms, which is 2:1, and much 
easier to tune in the shack. You need one or more parallel capacitors 
that have low loss at 1.8 MHz (to get the desired capacitance), and are 
rated to handle the current of whatever power you're running.  I've been 
doing exactly that for nearly five years, and it works quite well.

I found a nice selection of suitable caps at our local surplus house, 
HSC (also known as Halted) in Sunnyvale. I've stocked my junkbox with a 
broad selection of them, typically at prices of 40 cents to a buck a 
piece. It's a huge warehouse with surplus parts in bins. They have an 
online presence.  http://www.halted.com/

73, Jim K9YC