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

[RichardBJohnson at comcast.net]

The short answer is that from a field-strength perspective, it doesn't make any difference. From a transmitter perspective, whatever provides the best match over the greatest bandwidth is better. Often, when building a unipole, nobody bothers to adjust the drape wire length for a specific matching impedance (because it doesn't make any difference). The fine-matching is done with the ATU.

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

----- Original Message -----
From: "Scott Bailey" <wmroradio at bellsouth.net>

I have rather a stupid question to ask and I hope to get a simple answer. Is it best when tuning a tower that has a unipole on it to 50 ohms or 70 ohms?  My unipole is tuned to 70 ohms and I wondering if I would get better efficiency if it was tuned to 50 ohms on the antenna side of the ATU.

My transmitter is looking at 50 ohms going into the ATU, but the antenna is tuned to 70 ohms. Can one of you guys tell me which is best. The engineer that put up my unipole told me that 70 ohms was the best because it kept the signal more towards the ground. I have no clue about that theory is true or not?  I'm sure the brain trust here can give me the right advice!

Thanks,
     Scott