Originally posted by snowcat
I can get WSMV through a Silver Sensor too. But why does it work? If it is UHF only, how can it pick up VHF signals? I am not complaining, but I am curious.
Any piece of electrically conductive material (metal) will pick up TV signals, on any channel. I work for WSMV; when testing a DTV set-top box recently, we just stuffed a paper clip in the antenna jack - and received our own signal just fine. Of course, we were 1500 feet from the transmitting antenna! (though we did pick up three competitors from as far as five miles away...)
The idea of the Silver Sensor (and indeed pretty much every worthwhile UHF antenna) is to connect several antennas together. By carefully arranging the size of these antennas and the connection arrangement, it's possible to cancel out unwanted signals and noise coming in off the sides and back, and reinforce signals coming from the desired direction.
The Silver Sensor is a "log-periodic" design. This means that it works as intended across a range of frequencies, roughly a 2:1 range. This is enough to cover the UHF TV channels, which lie between 470 and 890MHz. (OK, that includes obsolete channels 70-83) Larger log-periodic antennas are used by hams to cover the 14-30MHz shortwave spectrum.
VHF TV is much lower in the spectrum. Channels 2-6 are 54-88MHz; channels 7-13 are 174-216MHz. These frequencies fall well outside the 470-890 range where the Sensor is designed to operate. In fact, no single log-periodic antenna would behave as a log-periodic in any two of these channel ranges.
The Silver Sensor *does* still pick up VHF signals - after all, it *is* a chunk of metal. It just doesn't exhibit the predictable cancellation & reinforcement properties it does for UHF. It will likely pick up interference and noise from other directions. It's also too small to be really efficient at picking up the longer waves of VHF stations. (the length of a radio wave grows with decreasing frequency/channel number; channel 10/200MHz signals are about 1.5m/5' long, while channel 17/500MHz signals are more like 2' long)