AM is very directional-I listen to a Boston Station (WRKO), 50,000 watt power. This station is almost impossible to hear in Leominster (about 50 miles west of Boston)-yet it is clear in Montreal (320 miles north of Boston). I’ve picked it up (at night) in Ft. Lauderdale, Fl. (1700 miles south of Boston).
The weird thing is: WRKO carries local news and Boston-related talk radio-and they get people calling in from Montreal! I don’t know why anybody in Canada would find Boston politics of interest.
Isn’t there a short story (I want to say Damon Knight) where a guerilla group basically rediscovers AM radio and use it for communications while fighting an enemy that only uses FM and basically doesn’t know that AM is even possible?
From the coverage maps, it looks like WRKO’s signal reaches further from north to south than it is from east to west. Atmospheric conditions also play havoc on AM radio signals, which is probably why you heard it in Florida.
As to why people call in from Montreal, who knows. Some people listen for the novelty of hearing distant stations. Boston is the largest American city to Montreal, so that may have something to do with it.
Robin
Not out of Windsor, though. Only Toronto, Montreal, Vancouver and Ottawa.
Robert Heinlein has a rebel group on Venus using it as the “slaver” negacorps that run the “indentured service” projects all have FM gear.
To return to Ekers’ Star Trek comments, who’s to say that aliens will chop up the radio spectrum the same way we do? IIRC, how many cycles occur in a second determines what the frequency is. If aliens have a different definition of what a “second” is (as they most certainly will), then they won’t “see” the radio spectrum as we do. We may think that 800 Mhz is a fine band to broadcast on, but to them, we’re broadcasting on 746 Mhz and 747 Mhz, so we sound like static to them.
However, your idea of using a frequency for low detail information isn’t a bad idea at all. In fact, the New Horizons probe now on it’s way to Pluto, is using just such a system. Instead of beaming back detailed telemetry of what’s going on, it simply sends back a tone, with the nature of the tone indicating the status of the probe.
Does anyone broadcast on LW in the US, or is that a British definition of part of the AM band? I used to get BBC Radio 4 on LW when I lived in Ireland, and have picked it up in the middle of France too.
Hmmm. It looks like British LW (Long Wave) ranges from 30 to 300 kHz, whereas U.S. AM radio ranges from 540 to 1710 kHz. (Canadian too, I assume?) Frequencies below 300 kHz seem to be mostly reserved for maritime communication and navigation, over here.
(Links: (1) A page on UK radio bands; (2) A PDF showing U.S. frequency allocations.)
AM in itself is not directional. The FCC requires many standard broadcast stations to operate with a directional pattern to reduce interference between stations. This is accomplished with some combination of multiple antennas and a phasing unit to tweak the signal supplied to the various towers in order to produce the desired pattern.
I would guess that WRKO uses a simple system - two towers spaced half a wavelength apart, lying on an east-west axis, and fed equal power, in phase. With this arrangement, at any point on the east-west axis the signals from the two towers would cancel each other out and produce nothing. Points on the north-south axis would receive the full signal. Other axes would receive less signal, depending on the location. The pattern is a simple figure-8. (Doubtless way more than you wanted to know, but durnit, I was proud of that FCC radiotelephone operator’s license I used to have. . . .)
(At AM broadcast frequencies the entire tower is the antenna; groups of AM towers are known by the rather quaint term antenna farm.)
For what it’s worth, you’ll find most of those callers from the 3-7PM Howie Carr show. He is syndicated to other Entercom (?) stations, one of which is in the northern part of VT. That signal is how most Canadians are probably getting the show.
I once bought a multiband radio in europe-and it has the band below AM (540 KHz). There is one staion on long island, NY-it broadcasts surf reports at 300 KHz-other than that, it’s navigation systems.
Question: if you modified an AM receiver-could you pick up the US navy’s ultralow frequency shore-submarine channel? I think it operates at something like 90 Hz!
Suppose you could. Course, at that low a carrier frequency it’d have to be data, not voice (and I figure a theroretical maximum of about eight bytes per second!).
Not by its nature, but by antenna systems designed for that purpose. If your intended local audience is located mostly north or south of you (perhaps due to a large body of water to the east or west), you want to concentrate the signal in that direction. With the same amount of input power, your signal will carry farther where it does the most good.
With regard to the “why didn’t shortwave take off for car radios?” question, I always thought it was a chicken/egg question. With radio equipment relatively expensive, car manufacturers weren’t likely to include them if there was no demand, and there was no demand because most people couldn’t receive them and didn’t know why they should want to.
A similar situation happened in the FM spectrum circa 1950-1960, at least in St. Louis and probably other large cities. In those years, there were only 2 stations on the entire FM band; most people didn’t have an FM radio and there was very little reason to start a new station (chicken/egg again). It was only when the number of stations reached “critical mass” that people began buying FM radios and eventually radio receiver manufacturers included both in most radios.