Re: KNSG testing on-air
sdwulfdawg said:
Big 121 said:
Playing etherial, soothing New Age instrumental music. Somewhat spotty Lakeside/Santee, driving around where KSDS Xlator interferes. In home, only the best portables receive it "listenable".
Although their CP calls for H&V polarization, they saved buck$ and went horiz. only.
I've never quite understood horizontal/vertical antenna polarization concept....could someone explain this?
Maybe this analogy will help (or maybe not):
Imagine you're the transmitter, and you're holding one end of a long rope. The other end of the rope goes through the mail slot in the front door of a house, and then is tied to the coat rack inside.
You start wiggling the rope from side to side. Your movements are transmitted down the rope, through the mail slot, and into the house. Anyone watching indoors will see the rope wiggling inside the front door.
Now, imagine that instead of wiggling the rope from side to side, you wiggle it up & down. It continues to wiggle for most of its length -- but the mail slot opens the "wrong" way -- horizontally instead of vertically -- so your wiggling motion doesn't get transmitted through the door & the person watching inside won't see much motion at all.
That's kinda what horizontal & vertical polarization is for radio. You can "launch" the radio waves either horizontally or vertically. The receiving antenna must match for most efficient reception.
In nearly all cases, the FCC requires FM and TV stations to transmit horizontally. They determined in the 1940s that manmade noise tends to be vertically polarized, so if receiving antennas are horizontal they'll reject much of this noise.
Stations may optionally choose to transmit both horizontally *and* vertically. The vast majority of FM stations have chosen this option. As I'd imagine you've noticed, most car radio antennas are vertically polarized. With most other radios, the polarization is simply hard to predict! It's a lot rarer with TV, because a TV set is* more likely to be attached to a proper horizontally-polarized antenna. (see below...) Going both horizontal & vertical is more expensive, because you need to provide twice the transmitter power. (one batch of power for each polarization)
A small number of FM stations in the 88-92 band are required to use vertical to reduce interference to TV stations in the 82-88 band. ("channel 6"). Since the TV stations are horizontal - and a TV is* more likely to be attached to a proper horizontally polarized antenna - having the FM station go vertical knocks down its signal at the input of the TV set. Since TV has gone digital, there are far fewer stations broadcasting on this 82-88 band. Indeed, just yesterday an FM station on 88.5 in Pennsylvania applied for permission to go from vertical-only to both horizontal & vertical.
*
was more likely; today, with most over-the-air TV viewing using indoor antennas, TV has the same problem as FM -- you can't predict what polarization the receiving antenna will prefer!