So explain to me the differences between full service, secondary service and third? is there a third ?
John
On AM, you have
Class A (or Clear Channel status) where the station is allowed to broadcast up to 50kw non-directional, and they have the full rights to their frequency, and in the case of true "clears" like WHO, WGN, WABC, KSL, KOA, WBAP, KNX, etc. then no station within 750 miles is allowed to broadcast on that frequency at night. As a result, let's look at KOA. During the day, it can be followed into Kansas for around 300 miles on a good radio and good day. But at night, it can be picked up on the West Coast of California. (There, it is obviously a bit weaker, and subject to more fading, but there it is, providing world-class content to a good chunk of the US. KOA is as clear as a whistle whenever I travel for vacation, so I can even depend on it whilst in Sheridan, Wyo to keep me company.)
Class A to B: Stations like KDWN, KOMO, KKOH, KKOB, KTWO, and whatnot are stations that may broadcast up to 50kw around the clock if they protect the main stations (in this case, WGN, WMVP, WBBM, WABC, and WBZ). They are still allowed to be 50kw non-directional during the day-time, affording some sweet coverage still. All 5 stations I mentioned also has protections of their own, but just not as stringent. A look at KTWO shows this. WNVR, a station in WBZ's zone powers down from 10kw to just 120w. KMAS, a station in KTWO's zone, only goes from 10kw to 1kw. A true Class A will run at 50kw all the time and just directionalize if needed. But, there is an interestingly different option to pursue as we'll see below...
Full Class B: KMAS is a Class B station. So is KGYN, and KHAT. All three runs 10kw daytime, but they are different at night. Flexibility is to be expected on Class B. KGYN remains at 10kw during the night, but goes directional to the NW, to protect Class A station WPHT. (KGYN, by the way, has a CP for 22kw daytime, and KDFD runs 50kw daytime, which again shows the available options for a Class B station.) KMAS goes down to 1kw at night, but is non-directional. KHAT also goes down to 1kw, but is directional, to protect KGYN and WPHT. There is also things that are odd, like KRKO being 50kw ND daytime, but then throwing everything to Alaska at night (Still at 50kw).
Class C's are considered the "Local" class because they really hone in their coverage to their hometowns. By law, these stations operate on 1230, 1240, 1340, 1400, 1450, and 1490. They are only permitted a maximum of 1kw (that's 1000 watts) during the daytime. Although most stay on 1000 during the night, some will drop it down. WHIZ in Zanesville Ohio does 1kw daytime and 960w nights. WPSE Erie does 1kw says and 770w nights. The opposite is true as well. KJMU Sand Springs, Oklahoma goes up from 500w daytime to the full 1kw nights. Stations in Alaska, Hawaii, and Puerto Rico treat these frequencies as Class B due to their distance from the mainland.
Class D: The leftovers. These stations can go as high as 50kw daytime, but they must be under 250 watts at night, and they, in general, must accept any interference from other stations, including other Class D's or higher. If there is ambiguity, the higher Class station gets priority. On 1480 AM, there are Class B and Class D stations. The Class B ones are already working within their own rules, but they have precedence over any Class D sticks. Therefore, KLMS and KQAM (Class B) may go right over the top of KRAE at night. Often times, despite being within 5 miles of KRAE, I can often null them in favor of KQAM in particular. And again, KRAE (Class D) is lower in class than KQAM, and therefore accepts all interference from KQAM. However, KRAE, limited to 72 watts at night, is not allowed to cause skywave interference to KQAM. (Groundwave, however, is fine.)
In fact, the rule applies across the entire band. KGAB (Class B) is a beast during the daytime at 8.5kw, but WSM, being Class A, is allowed to cause interference to KGAB, which does occur every once in awhile. KGAB is far enough away from WSM to be allowed to be on at night, and runs at 500w during that time, allowing it to be heard across a good chunk of Wyoming and Southern Montana. KGAB and KMTI are the same class, thus none has the priority over the other, and each other's skywave collides in Eastern Idaho.
So FM is a bit different.
Class C's are the big boys and get the farthest coverage, particularly C0's. C0's to C3's are all able to go up to 100kw, but the antenna height differs. Sometimes you will see grandfathered stations under just Class C without the number, and right now, the highest powered US station is WBCT Grand Rapids, MI, with 320,000 watts under it's belt. The thing is, FM, because of the Earth's curvature, has a finite distance it can travel whilst on Earth, but the signal also spreads infinitely into space. 320kw, though, fills up offices 50 miles away better than a 100kw can, however, a 100kw is very sufficient at reaching car radios, and once you get past a certain point (probably 65 kw), the distance can't be improved anymore. In fact, if you look at Colorado Public Radio's flagship, KCFR, it is only 14kw, but in my opinion, it makes the 100 mile trip to Cheyenne as good as any of the higher power stations. So when you see a construction permit for higher power, think penetration into downtown offices rather than increased distance. KXWA and KIGN are both on 101.9. KIGN is a lot higher at 50kw, while KXWA is only 9.5kw. In Kimball, 63 miles east of Cheyenne, or 130 miles NE of Denver, these two stations battle it out, and literally as soon as you get south of the welcome center, KXWA (remember, 9.5kw and 130 miles) is way on top. It blew my mind the first time it happened, but it's proof that wattage doesn't matter as much as transmitter height and receiver height. With that note in mind, let's move on.
*I should add that Class C's are banned in a good chunk of the North-east, and California. There seems to be no reason for this except to preserve frequencies in extremely urban areas.
Class B's are only allowed 50kw, and a maximum HAAT of 150m, similar to Class C2.
Class A's are only allowed 6kw, and it's more common to see them in smaller communities anyways.
Class D's are reserved for small time educational stations, particularly in Alaska (10 watts max), but they are also translators (250 watts max).
Low power stations are their own unique system. At most, they can broadcast with 100 watts, and they are only meant to serve a VERY SMALL community. These smaller stations are easier to build antennas for, hence they can get closer to their community. Some do very minimalist work, whilst others go all out (like KWYG-LP, 80 watts) and can cover a decent area. A special subset of LP stations are only allowed 10 watts in more urban areas.
Finally, there are some legal ways of broadcasting without a license, but even compared to a Class D service, they use a LOT less watts. Like somewhere in the nanowatt realm. (And THAT is miniscule compared to even 1 watt). Even so, they can travel a few city blocks, or upwards of a mile. This is the U class or Unlicensed class. Examples of legal operation is a car-transmitter with Bluetooth, a church service, a Christmas lights display connected to FM, and of course, a designated SiriusXM repeater. So, in my community, someone does run a lights display running a playlist on 107.7. It travels for a good 0.75 miles or so under the right conditions, and it gets staticky about 5-8 streets away. I've had several people running their car transmitters, making for some interesting finds as I drive around town. Most of them are good about finding an open frequency, but I was not thrilled when someone plopped their transmitter over KXKL. You just don't mess with classic hits! Another example of an unlicensed operation in my town is on 90.7 FM, which started out playing straight up Sirius XM, but I noticed a couple of weeks ago that they started changing some things up. Some local ads would pop up (and then more as of this week), some programming that didn't seem like it was coming from XM, and then on weekends it would switch to old-timey programming. It's practically halfway to being a full-service type of station! Now of course, if that's what the person needs for their house, then that's legal. However, if they make any attempt to claim a "broadcast" (be on the lookout for a DJ, or some sort of slogan like "Surfin 103.7"), than that will be illegal to the FCC without a license. 90.7 in my town teeters on the edge of legality in terms of programming, but it is well within it's power range as it basically only covers about three medium parking lots.
So lots of options there.
So hopefully this guide provides a good rule-of-thumb for the stations you are interested in!
I feel like I went a lot longer than I probably needed to, however I hopefully broke it down in a sensible manner that wasn't too hard on the eyes. I am just a bit passionate about radio
