10395Horizontal Loop Antenna For Digital TV
- Jan 13, 2014I was recently reviewing online designs for homemade DTV antennas. Most of these designs are for UHF (channel 14 and up) and are of the general design of multiple V dipoles with a phasing line, in front of a reflector screen. These antennas are directional, and have to be aimed at the transmitting tower. In my particular location, rural open space with no multipath problems, I wanted an omnidirectional antenna (or at least one with 180 degree coverage) that covered VHF high 174 MHz up through UHF.
Searching through Internet postings for omnidirectional DTV antennas, I found a couple of descriptions for horizontal loop antennas. THese have been constructed of 1/2 or 3/8 inch copper tubing, in a horizontal loop of about 26 inch diameter, feeding a standard television 300 to 75 ohm balun and coax cable. They are typically supported with a horizontal PVC cross and mounted outside on a roof. In one design the loop is a complete circle except for a gap at the feed point. In another design there is also a gap 180 degrees across from the feed point.
I tested this design by picking up a slightly damaged aluminum bicycle rim (about 22 inches diameter) for two dollars at a used bike shop. I cut out a one inch gap and attached a balun transformer with two screws through existing spoke holes. I tried this antenna indoors horizontally on a table next to a large window, and picked up 14 digital channels, both VHF and UHF. Based upon the signal strength meter in the TV, this antenna was omnidirectional on some stations, and semidirectional on others. On those channels where there was some directionality, it seemed to favor the feed end of the loop. It still had a wide beam width on these channels, though.
I made a second horizontal loop out of heavy wire so I could test the effect of a gap 180 degrees from the feed point. This increased the signal strength on some channels, but caused me to lose other channels, so I only got 11 instead of 14.
The aluminum bicycle rim is cheap, rigid, rustproof and easy to come by. It will be easy to mount horizontally outdoors, where I expect it to perform even better. This might be a good platform for other loop antenna projects as well.
DTV receivers do not handle multipath well, so this would probably not be the best antenna in an urban environment, but for a more open area with various towers in different directions, it seems to work well.