I am listening to CBC Radio One’s Saturday Night Blues program. Yet another good radio show that comes in here via skywave from CBE in Windsor, Ontario. It is in the process of migrating to the FM band, channel 248B (97.5 MHz) after which the AM station will be turned off after a three-month simulcast. I know I can stream this program, but that is a pain because it slows my computer down, plus, it does not sound as good coming from the computer speakers as it does from the AM radio even with the occasional fade.
According to the FCC website (yes, the FCC has records of Canadian, Mexican, Cuban, and Bahamanian radio stations), it is a class A station with a 2-tower directional, 1/2 wave towers with 10,000 watts, unlimited. Pattern nulls to the south with a big fat main lobe north, east, and west.
I wonder what they are going to do with the transmitter when they turn the station off. I wonder what kind of transmitter it is, sounds like a tube unit to me. Certainly sounds good with that old blues music tonight.
We have a few stations that are currently encoded with the Arbitron PPM encoders. I did a little research on the encoding method since it is not immediately apparent how they are transmitting their data.
Arbitron PPM encoders
According to Wikipedia, which can sometimes be relied upon, Arbitron used Martin Marietta to help develop the technology. Martin Marietta (now Lockheed Martin) is mostly known as a defense contractor, they have helped develop several complex military communications systems over the years.
There are no fewer than 39 US patents that cover the technology used in the PPM. The most significant of these appears to be 7,316,025 which describes the psychoacoustic masking technique employed.
It really is pretty slick, using a sample rate of 8.192 kHz, it transmits 4 bits per second in the 300-3000 Hz range by hitting specific frequencies in that range at varying intervals, adapting to the audio levels to keep the encoding below the programming content. 4 BPS is very slow and thus very robust. After all, I believe the only formation transmitted is a six-digit encoder serial number. I did not read all 39 patents to see if anything else was changed in the encoding method, so it may be slightly different.
This type of system would have fairly low overhead, not adding to the station’s bandwidth which is a consideration for FM stations, and in the correct frequency range for most AM receivers on the market today. Some people have said they have heard the encoding on one of our stations, most notably during silence or very quiet programming. Perhaps, especially in a dead air situation, one might hear in nearly imperceptible low frequency slow fluttering sound.
If anything, the encoding is perhaps too robust.
Now for the deployment of the monitor technology, which has so many up in arms. As with other Arbitron ratings methods, the main bone of contention seems to be the size and distribution of the sampling hardware. Minority groups feel they are underrepresented because the PPM is unevenly distributed.
Rating samples always seem to skew one way or another. The data samples themselves seem to be too small to accurately predict a station’s listenership. One anomaly and the entire month or quarter can be thrown off. The PPM seems to correct some if the issues with keeping an accurately written diary. One problem with the PPM however, it can also pick up incidental background noise and count it as time spent listening (TSL).
Think of the cubical environment where somebody several cubes away might be listening to a radio station. To the PPM wearer, it is unintelligible background noise, however, because of the perceptual encoding, the PPM picks it up and it counts as several hours of TSL.
A broader sample would dilute this with other more accurate representations of radio listening. A broader sample would also alleviate some of the complaints from the Minority Media and Telecommunications Council (MMTC). First-year physics students would recognize that not enough sample data can make results wildly inaccurate. Or, as one emergency room doctor stated while washing my knee out with a liter of sterile water after a dirt bike accident, the solution to pollution is dilution.
This is an EIMAC 4CX3500A which came out of a Harris HT5 transmitter. As you can see the ceramic cracked in half. When I arrived at the transmitter site, the unit was on full plate voltage, with no plate current, and no overload lights. I figured it might be something with the tube, so I tried to pull it out, but only the top half came. One of those “Ah ha” moments.
Fortunately, there was a working spare at the transmitter site and we got back on the air relatively quickly. That, in and of itself is amazing considering the building that this transmitter lived in. One of those abandoned former studio sites with the transmitter jammed into a back room somewhere. To get to it, one has to dodge pigeons, beware of rats and wade through piles of garbage.
It is a little bit hard to tell in this photograph, but there are two “cages” which are the Screen and Grid. The post in the center is the filament/cathode and the top detached part is the plate/anode. In an FM transmitter, the exciter is coupled to the grid, and the screen accelerates electrons toward the plate and therefore controls the power, the plate collects the electrons and is coupled to the output stages and the antenna. Good stuff.
Another picture from my collection, this one is the back side of a power supply module from a Broadcast Electronics AM6A transmitter:
Bang!
It happened during power up from 1 KW to 5 KW and it was quite loud, as I was standing right next to the transmitter. The exploded part is a 0.1 uf capacitor that looks like an add-on. In fact, some of the other power supplies don’t have it. It also took out the 20 amp slow blow fuse.
I like the exploded look of the board, kind of like on The Road Runner, when Wyle E. Coyote looks into a box and something explodes.
This is the only problem I have had with this particular transmitter.
