J-Pole Antenna Build, Ohm question.

[Hoodcom]

Hey guys,

I read around for FM Antenna's and found out about the J-Pole Antenna here from searching. Using Hamuniverses J-Pole calculator, I have the pieces cut for 100MHz tuning here. (Just need two caps and a 1/2" T. )

This Antenna is for the office of my parent's business I work at, since the Di-Pole isn't enough for some stations, I figured I can do better with a J-Pole in the 2nd floor storage level in the shop building, directly above the office. Roof mounting is out of the question, but at least the Antenna would be higher up and able to be mounted securely with out much issues of running the cable.

Now according to the calculator, the Feed Point is 2.76 inches. I found a post or two, saying how the J-Pole Antenna is 50 Ohms. Some say you can increase the feed point dimension by 1.50 inches to get 75 Ohms that our FM Tuners expect.

Is this an accurate calculation, or would I be better off getting a transformer to go from 50 ohms to 75 ohms?

 

[Ed in Tx]

.. would I be better off getting a transformer to go from 50 ohms to 75 ohms?

I wouldn't be concerned about a matching transformer. 50 to 75 Ohms would give you a 1.5:1 SWR and maybe 1/10 dB loss from the mismatch.

 

[FauxHall]

One can match the antenna impedance to the feedline (75 or 300 ohm) by moving the feedline connection point up or down. Hook her up to a tuner with a good signal strength meter, tune to a station of interest, then move the connection point until one gets max signal strength.