[BC] 50 Ohms vs. 71 Ohms (AM Antenna Tuning) (Richard Fry)

[Jellison, Paul]

 Since I get the Digest version I will respond and hopefully this makes
it in to the list. 

RE 50 V 71 Ohms. The feed impedance has nothing to do with the antenna
take off angle. That is determined by antenna length for the most part.
I try to get the antenna system tuned to a sweet spot that offers the
most symmetrical reactance slope over the operating range of the
antenna. You may get 50 Ohms but really have some odd reactance swings.
Or it may be fine. However, what ever that reactance point is it allows
you to get optimal bandwidth performance out of the antenna. Important
if you plan on HD operation. But will require an ATU.
If you have a 50 OHM system you can get away with minimal ATU
components, if you tune if for 50 OHM operation. I have had them be as
simple as a series variable capacitor.

Regards,  

Paul Jellison
Regional Director of engineering
Clear Channel Dayton
101 Pine St. 45402
 

Message: 2
From: "Richard Fry" <rfry at adams.net>
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>Is it best when tuning a tower that has a unipole on it to 50 ohms or 
>70 ohms?  ...  The engineer that put up my unipole told me that 70 ohms

>was the best because it kept the signal more towards the ground.