Can't remember where I read it, this forum or another, but the question was if a balun made for TV will work at the ads-b freq, 1.09 Ghz. I'm using one now for ads-b reception. It's one of those cheap ones with no leads. It is a small black plastic block with two screw terminals for the 300 ohm connection and a "push on" 75 ohm male end made to connect to a jack on the TV. I made a small folded dipole from 18 awg magnet wire appropriate in dimensions for 1.09 Ghz. and attached same to the 300 ohm terminals. I opened the small plastic box, removed/de-soldered the 75 ohm connector and attached/soldered my 75 ohm coax feeder directly to the output of the transformer inside the plastic box. This arrangement is waterproofed with hot glue and was inserted in the end of a pvc pipe that was factory bent into a 90 degree configuration, purchased from a local home improvement store. The coax exits the transformer inside of the 90 degree pipe and down the 6 meter length mast into the home. The folded dipole is positioned on the pipe to be vertically polarized. The antenna is in a very poor location by necessity, since I'm in a rental home for now, but where it can "see" the horizon, it can track 'craft out to 200nm... again, it's only 6 meters or less AGL, so that's not bad at all. The bottom line is that a cheap TV balun does work at ads-b freq. and will perform well for a cheap and temporary antenna setup. I see no problem using a 75 ohm antenna system with the rtl-sdr, as opposed to the more common 50 ohm installations. Future plans when I am in a permanent home will be making a "double" 5/8th wave gain antenna and having the rtl-sdr mounted directly at the antenna instead of at the end of a long coax run in the home. Hopefully, I'll be also able to mount the antenna high enough to have a clear shot at the horizon for 360 degrees, unlike how the present antenna is poorly situated.
The quality of baluns made for Tv band is usually very poor, being the strength of received signals on a very different range. But the main point is, why should you use a folded vertical dipole and an impedance trasformer when a simple ground plane can do the work and be adapted to 50 or 75 ohm cables just changing the angle of radials?
Hi Jhonny, for a couple reasons: The first is that I just wanted to see if it would work... pure experimentation. Secondly, at other radio frequency ranges and modes, I've had excellent results with vertical half wave dipoles over GP's. As stated, i really can't complain about the results. If you could see where this antenna is placed, and it's comparatively low hight, it's hard to believe it could reliably decode at 200nm distance.
