[BC] Assistance with a tall tower

[RichardBJohnson at comcast.net]

A 1/2 wave is about 370 feet in free-space at your frequency. If I assume a propagation velocity of .95, which is reasonable for uniform cross-section towers, it would be 350 feet for 1/2 wave. A similar antenna that was "way too tall" in Phoenix/Tempe, AZ was 450 ohms + J200  (awful). The necessary minimum Q of the matching network reflected sidebands back into the GE 50 kW that would make it croak. I made some modifications to the GE to reduce its output Q, which (finally) let it stay on the air.

If you are an experimenter, this is a good place to install a folded-unipole with short skirts. This would get the impedance down as well as the reactance. You make the skirts slightly less than 1/4 wavelength in length. You can experiment with a single wire, a bridge, and a grounded antenna, before you spend any money

Cheers,
Richard B. Johnson
Book: http://www.AbominableFirebug.com/

----- Original Message -----
From: donroden at hiwaay.net

1240Khz on a guyed 310 foot tall / two foot face triangular tower.

Any "guestimate" on the series feed R and j ?

It's an old install ..... doesn't look like the conventional "T"  
network for matching.... More like a "pi-net" with a shunt cap at the  
coax input to ground. There are two series caps at the antenna input (  
presumably to bring a high value of +j down to a usable level ? ) a  
series coil 7 turns 6 inches dia
and then a homemade self supporting #12 wire coil to another cap to  
ground at the junction of the "pi" coil and the two series antenna caps.

I can't read the values on the caps .... too weathered.