> As an AM TX and general domestic AM dummy, what does all this mean, about > not being able to put a 1kW signal into some type of tower? What does the > power and or tower have to do with not being able to feed full power into > the antenna?
Different classes of stations are required to have a minimum efficiency from their tower. Put a kilowatt in and the signal strength at a kilometer away should be a specific number or more. Clear channel stations have the highest minimum. Regionals are lower. Locals like 1340 are the least. When a station is licensed at a specific power and tower height (efficiency) it's given an effective radiated power. When a station puts a kilowatt into a 5/8 wave tower it is about the same as putting 3+ kilowatts into a 1/4 wave tower. So, many times a station using a taller tower has to reduce transmitter output to keep the coverage the same. One of my clients on 1110 was originally a kilowatt non-directional into a 1/4 wave tower. They put in a much taller tower to add an FM. So, they had to drop transmitter power to around 680 watts. Same coverage on groundwave. 5/8 wave is the best height for a local station that isn't looking for coverage beyond 40 miles or so. There is a secondary high-angle lobe that comes back down from skywave and causes interference about 70 miles out. That's why the sweet spot for tower height for the big guns is a bit over half wave, 195°. Low band stations can reach the minimum with a shorter tower. For example, local WDDZ-550 has 1/6 wave towers but still meets the groundwave efficiency requirements. There are other problems with short towers, but that's a subject for another chat. WNBH is lucky in that they are grandfathered in for a full kilowatt into a tower that's effectively around a half wave. For a local channel station, they do cover well. And the fact that they are not far from the coastline gives some pretty interesting DX reports now and then. As I mentioned, this is the third report from Scandinavia in the past couple of years. The previous two were quite easily identified. Probably have the .mp3 of those around somewhere. Yeah, I probably ought to schedule some sort of DX test out of that station. Let me see what I can do... Again, thanks to all for the help. My ears aren't anywhere as good as they used to be... Craig Healy Providence, RI _______________________________________________ IRCA mailing list IRCA@hard-core-dx.com http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: irca@hard-core-dx.com