Topband: New install being put together

[George (K8GG) & Marijke Guerin]

Brian Gieryk wrote:

> Good morning all!
>
> I am in the process of building a "new" 160 station.
>
> The object is:
>
> 128' base insulated tower (located, I think)
> 1 kW Bauer 707 TX
> 7/8" rigid transmission line
>
> What I need is guidance in the design of an AM broadcast style ATU for
> the tower base.
>
> TNX in advance!
>
> Brian
> KE6IYC


K8GG replies:

If you are base or series feeding 128 ft of 45G tower, the approximate 
impedance is 37 ohms over a good radial system.


One suggestion:
With 75 ohm hard line one can use a 2:1 UnUn to drop down to the antenna 
impedance, or

2nd suggestion:
One can use a Pi-Network tuner or L-Net tuner at the antenna, or either 
tuner at the shack as the SWR will be only about 2:1.  There will be 
essentially zero losses in hard line from your shack to the vertical 
antenna.  I would use the L-network at the shack, as it is easiest to adjust 
if you have a good roller inductor and capacitor to build an L-net tuner, or 
use the TenTec 229 or 238 tuners.

GL  & 73,     George    K8GG