[Elecraft] Tuning Random-Length Wire Antenna with K3 Internal Tuner??

[Walter Underwood]

A random-length wire is usually chosen to avoid a half-wavelength on the frequencies you’ll be using. A more accurate term is non-resonant end-fed antenna.

Avoiding half-wavelengths means the impedance will not be 5000 Ω or greater, but it will be pretty high. Or low. The SWR on the feed line will be large and a high impedance feed point is pretty sensitive to surrounding objects (capacitance).

So:

1. Keep the coax short and low loss.
2. At the antenna, connect some sort of counterpoise or RF ground to the shield of the coax. This can be a ground rod, a radial system, or a wire laying on the ground. If you don’t do that, the RF ground will be the coax and everything connected to it, including your K3.
3. After that, tell the ATU to tune it and wait for it to find a solution.
4. If it won’t match, change something. Maybe the length of the wire, maybe the position, maybe the counterpoise. 

If this is a long-term setup, a common mode choke near the rig is a good idea. Even with a counterpoise, some of that RF energy is going to be on the shield.

For field deployments with the KX3, I run with no feed line at all. The antenna wire and counterpoise wire are connected directly to the KX3 with a double binding post adapter.

wunder
K6WRU
Walter Underwood
CM87wj
http://observer.wunderwood.org/ (my blog)

> On Dec 12, 2020, at 9:41 AM, Mister Mike <w1rc at near-fest.com> wrote:
> 
> What is the best way to do this?  I am not familiar with automatic tuners.  
> 
> TIA,
> 
> Michael, W1RC
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