There is a very good blog called Arcane Radio Trivia which publishes interesting tidbits of radio trivia, and a lot of stuff that a reader might not have heard before, hence the name. A post put up last week, when I was out of town, deals with carborundum (Silicon carbide) which is one of the first semiconductors used to produce diodes, and thus detectors for radio.
Certain naturally-occurring minerals can be used to detect radio signals, including galena, zincite, silicon,bornite and others. Carborundum was unique among the early crystals because it was synthetic. It was durable, and at 9 mohs much harder than most available crystals. More here. Also interestingly it requires it requires a negative potential of 1 volt to be used as a diode. Carborundum was not created with this purpose in mind. It was created in the early search for artificial diamonds
Like many things in early radio, there are several plot twists in this story and if one is interested in radio history, it is work a click to read. While you are there, check out “It’s 105 degrees and rising“
I was digging through some old manuals at the shop today and I found this June 1987 memo from Orban to AM stations titled “AM radio CAN sound almost like FM.”
The main purpose of the memo was to get AM radio stations to implement the NRSC standard for pre-emphasis and high-frequency roll-off to improve the sound of AM broadcasts on ordinary radios.
I am not sure why the receiver manufacturers never designed an IF filter that would be compatible with NRSC, it seems like a fairly simple design. Instead, what we have is “digital” AM radio (IBOC) which does not work well, and creates many more problems with interference than pre-NRSC broadcasting.
If one were to look at the entirety of AM broadcasting history, one would find some striking parallels with what is happening with IBOC today on both AM and FM.
To start, the NAB began petitioning the FCC to allow more AM broadcasting stations, even as it was known that these stations would create interference with existing stations, especially at night. Still, the NAB persisted and the FCC relented and through the fifties, sixties, seventies, and eighties many more class II and III stations were established on what used to be clear channels (classes I and IA).
Once the AM band was chock full of stuff, they began going to work on the FM band with 80-90 drop-ins.
You see, for the NAB, more radio stations means more dues money, and greater lobbying power because of the larger size of the industry. Then came the deregulation of ownership limits. By this time, Big Group Radio was calling the shots and they wanted more. This led to the great consolidation rush of the late 1990s from which the radio industry is still reeling. The consolidation rush led to highly overpriced radio stations being leveraged to the absolute maximum, leading to recent bankruptcies.
Finally, the NAB’s great push toward adopting IBOC digital radio in the early years of the 00s. IBOC was supposed to save the day, greatly improving the quality of both AM and FM and bringing radio into the 21st century. Except that the promised technical advances never materialized. IBOC remains a great expensive boondoggle and I am beginning to think that perhaps we should stop listening to the NAB.
The memo itself is a fascinating thing, which was one could substitute AM with RADIO and come to some of the very same conclusions today regarding analog and IBOC digital radio. For example, this paragraph on AM stereo:
AM stereo was thought to be an answer (to improve AM), but AM stereo was embraced with the false assumption that having ‘stereo’ automatically meant having ‘high fidelity’. While AM stereo did provide somewhat better fidelity, it was not comprehensively engineered to get the best fidelity from AM. It was hoped that the gimmick of having two channels would be enough to save AM.
AM stereo could have been an improvement, had it been properly implemented. Unfortunately, the underlying problem of bad-sounding receivers was never addressed. About which, the same memo notes:
Receiver manufactures did what they could to reduce listener complaints – – they narrowed the bandwidth (thereby reducing audio fidelity) until the complaints about interference stopped. Listeners clearly indicated, through their buying habits, a clear preference for lower fidelity over continuous irritating static, buzzes, whistles, and “monkey chatter’ from adjacent stations. People accepted this situation for a long time – – until the simultaneous advent of improved receiver technology and the FCC’s anti-simulcasting rules created the FM boom of the late 1970’s. (ed note: I remember listening to FM because there were fewer commercials, not better sounding audio)
Then the memo goes on to stress the importance of implementing NRSC standard for AM broadcasting that included the sharp frequency roll-off at 10 kHz, noting that receiver manufacturers would design “fine new receivers” that would take full advantage of the new standard, but only if broadcasters first showed good faith by widely and promptly implementing it.
As I recall, NRSC-1 was adopted as a rule of law by the FCC in 1989, about two years after this memo was written. One could reasonably expect that receiver manufacturers then started producing radios that took advantage of the NRSC pre-emphasis curve with IF filters that did not cut off audio frequencies above 3.5 kHz, but rather rolled them off in a gentle slope until about 7 kHz, more aggressively after that until 10 kHz, where they cut off.
Except they didn’t.
Instead, twenty years later, AM radios universally sound bad, with an audio bandwidth of about 3 kHz or so.
I believe that AM receivers could be made with three IF bandwidths, automatically selected based on signal strength. Within the 5 mv contour, full (10 kHz) audio can be reproduced using a high-frequency roll-off described above. In the 1 – 5 mv contour, a 6 kHz bandwidth and less than 1 mv a 3 kHz bandwidth. The automatic selection could be defeated with a “wide/narrow” IF bandwidth selection switch like the GE super radios have. Of course, if one were listening to stations transmitting AM IBOC, the “narrow” setting would be the best.
Half of me thinks that the ship has already sailed on AM broadcasting. The stations on the air will continue to decline until they are no longer able to broadcast due to expensive repairs or replacement, at which time they will be turned off. The other half thinks that AM radio, as evidenced by the huge public response to WEOK and WALL broadcasting the true oldies channel, can be revived. With the impending inevitable FM IBOC power increases, translator shoe-ins, LPFM, etc; the FM band may become worse than the AM band. At this point, the public will have to decide whether free radio is important to them, or 3G/4G services will become the new method of broadcasting.
I just found my old copy of the NAB Engineering Handbook, sixth edition. I have enjoyed thoroughly looking at the AM antenna sections. It reminds me, that while we tend to think we have come up with new answers to old problems, really most of this was figured out a long time ago, this particular edition was copyrighted in 1975.
It is a thick book and covers AM, FM, and TV broadcasting technology as it was understood in 1975. There are several chapters about “current” things that no longer apply, there are also many very useful items, such as studio construction, AM and FM broadcast antennas, tower maintenance, and so on.
I will keep this on my shelf because it is an interesting primer on AM broadcast antennas with all attendant formulas and charts. It is quite interesting and fun if one is looking for the theoretical efficiency of a 185-degree radiator at 1 mile. I remember WPTR (now WDCD) in Albany had a three-tower with 206-degree radiators, 50 KW carrier power on 1540 KHz. It seemed to be quite effective, when I was chief engineer there, we used to get reception reports from South Africa.
Perhaps one day, I’ll put some of that information to good use with an AM station of my own.
These were broadcast platforms that were usually anchored in international waters broadcasting popular music to several European Countries including Great Britain, Holland, France, and Spain in the late 1960s through late 1980s. The reason for these peculiar operations was strict government control of all broadcast outlets and programming in those particular countries. The BBC was known to be stodgy and repressive of new music, particularly rock music from bands like the Rolling Stones, the Beatles, the Who, the Kinks, and others.
At the time, there was no specific law preventing ships anchored in international waters from broadcasting to shore-based listeners, a loophole in the government control was found and exploited. That loophole has been closed in most places, so as they say, don’t try this at home.
At one time there were several ships out there in the English Channel and coastal Denmark. The first and best-known of these was Radio London or “The Big L.” It broadcast on 1133 KHz from December 16, 1964, to August 14, 1967, using a 50,000-watt RCA ampliphase transmitter. The ship itself was the M/V (motor vessel) Gallaxy, a converted WWII minesweeper formerly known as the USS Density. After Radio London went off the air, the ship was transferred from port to port until it ended up in Kiel, Germany, where it was finally scrapped in the late 1990s.
Radio Caroline was the main offshore competitor, broadcasting on 1520 KHz and several other frequencies off and on from 1964 until 1990 or so using several different vessels to transmit from.
MV Galaxy with radio mast
One incident in offshore broadcasting that has always fascinated me was the burning of the Mebo II, then transmitting Radio Northsea International off the coast of Holland (this ship moved around quite a bit) in 1971. Later investigations revealed that the staff of an offshore competitor, Radio Veronica, was responsible for the firing of the ship. Apparently, in those days the competition was brutal.
I like the nice calm music with the increasingly frantic DJ (West, no East). In any case, the ship remained afloat and returned to the air the next day. The final European offshore broadcaster was something called Laser 558 on M/V Communicator. It broadcast using to CSI 25 KW AM transmitters on 558 KHz in 1983, again, off and on for several years until 2004. The CSI-grounded grid transmitters may have been inexpensive to purchase, but I’ll bet they cost a lot to run. This would be especially true if one were using diesel generators as the main electrical power provider. As a result, they were usually run at about 1/2 power. Eventually, M/V Communicator ended up beached in the Orkney Islands off of Scotland.
The only such attempt in the US was Alan Wiener’s MV Sarah, known as “Radio Newyork International” anchored off of Jones Beach on 1620 KHz. The owners figured 4 miles offshore was far enough to be in international waters, but the FCC felt otherwise, I believe at the time, 12 miles was (and still is) the territorial limit for the US. Four miles was not international waters, as the broadcasters claimed. These guys were arrested and sent to trial. After several years all charges were dropped.
Anyway, an interesting bit of radio history. Goes to show the lengths that some will go to when feeling repressed.
