I posted this on the Ramsey site as well:
I have seen lots of examples using TV rabbit ears vertically polarized as a transmitting antenna. The antenna is fed with RG6 through a balun. Since a dipole is in the vicinity of 70 ohms, why not feed the antenna directly elimiminating the insertion loss created by the balun? A simple clamp-on ferrite near the feed point would reduce or eliminate radiation of the shield. Comments?
The direct connection of the rabbit ears makes sense, what I would like to see is a comparison test between both methods to know the results.
I'm guessing you are doing this in the VHF region.
A "rabbit ear" dipole extended to about 1/2 wavelength will have, as you mentioned, an impedance near 75 ohms and a balun is not needed for impedance matching but there is another problem which a balun can help solve. That is the feed signal from the coax is not balanced to ground yet the dipole is at the feed point. This produces radiation from the feed line which distorts the pattern. A 1:1 balun will correct this problem by providing a balanced signal feed at the antenna feed point and is not there for impedance matching. A clamp on ferrite as you propose is often used to prevent feed line radiation so this may also work.
Sometimes a folded dipole is used and this antenna has an impedance of 300 ohms. For folded dipoles a 4:1 balun is used for the impedance matching as well as to provide a balanced feed.
Space permitting, I prefer to use a 1/4 wave ground plane antenna for 2 meter work. The characteristics of this antenna are predictable and the antenna is easy to build.
Neil
Wouldn't the balun reduce the feedback of rf into the transmitter as well?
I could try this both with and without the balun as a comparison using the folded dipole i built for Rock 105.3. My dipole is fed with 1 mW of rf power from a Ramsey FM 25B using 75 ohm coax and is leaning up in a corner of a room. It covers roughly 300 feet in all directions. Plans for the antenna can be found here, it is basically the same thing Ramsey sells but a lot cheaper. As soon as i have the free time i will test this out and post my results here.
