AM – Page 23 – Engineering Radio

Implementing MCDL (Modulation Dependent Carrier Level)

Since the FCC waved some of its rules regarding carrier power and carrier shift on the AM broadcast band, AM stations are now able to implement MCDL or DCC (Dynamic Carrier Control) technology to save money on their electric bills. This technology has the potential to save tens of thousands of dollars for higher-powered AM stations (high power=greater than 10 KW carrier level).

On a standard AM broadcasting station, the carrier represents two-thirds of the energy being transmitted, with the modulation index containing the other one-third. The carrier contains no information; it is simply there on the center frequency at the power level authorized by the station’s license. Thus, if the carrier can be reduced without affecting the quality of the broadcast reception, it will reduce to the overall power consumption of the transmitter. In areas where electric costs are high, the savings can be substantial.

There are various ways to accomplish this. The first is called Dynamic Carrier Control (DCC), where the carrier voltage is reduced during moderate modulation levels (between 20-50%) and restored during peaks. This reduces the output power during average modulation, restoring most of it during quiet periods and peaks. The next is Dynamic Amplitude Modulation (DAM), which is similar to DCC. The most savings will be noted with less heavily processed programming such as talk radio because the higher the average modulation density is, the less the MDCL circuit reduces the carrier voltage level. The little graph in the diagram shows the reduction in the carrier voltage vs. modulation levels.

Nautel DAM block diagram, courtesy of Nautel, Ltd.

Finally, Amplitude Modulation Companding (AMC) reduces the voltage in both the carrier and modulation product during peaks. This results in better savings for higher-density modulation indexes. It is also the most transparent of the three schemes, as the carrier is restored to full power during periods of low or no modulation levels. During peak modulation, the reduction does not drop the power level below the un-modulated carrier level. The little graph in the diagram shows the reduction in the carrier voltage vs. modulation levels.

Nautel AMC block diagram, courtesy of Nautel, Ltd

Nautel has done extensive work on MDCL and includes several algorithms in their NX series transmitters. For older Nautel transmitter models such as ND, XL, XR, and the J-1000, there is an outboard exciter, which is in a one-rack unit chassis. Older transmitters may need a simple field modification to create a DC-coupled audio input. The cost for the upgrade is approximately $5,000 USD, however, check with the regional Nautel sales rep.

Once the system has been installed, there are several things to be aware of:

Modulation monitors may not work properly, especially older units, which will show significant carrier shifts and have carrier alarms. Belar AMMA-2 modulation monitor is specifically built to work with MDCL transmitters.
When making field strength readings, the MDCL circuitry must be turned off to get accurate readings.
For stations running IBOC, the amount of carrier power reduction may need to be experimented with, as the effect of the carrier reduction may cause the transmitter to exceed the NRSC mask.

Currently, only Nautel and Harris are selling MDCL transmitters. I spent several minutes poking around the Harris website and looking through their product brochures for the DX series transmitters and no mention of DCC o MDCL was found. I’d be happy to include any information from Harris if it were made available.

More news talk migrates to the FM band

Once a bastion of the AM dial, News and or News/Talk format radio stations seem to be springing up on the FM band more and more often. The original premise for creating talk radio on the AM band was the lower bandwidth and reduced (or perception of reduced) fidelity when compared to the FM band lent itself to non-music programming. The reality is that receiver manufacturers never carried through on the NRSC-2 technical improvements, and AM receivers reproduced thin, low-quality audio. I digress, the story goes, the FM band was great for music and the AM band did well with information and talk.

Of course, there were always a few exceptions to those general rules, but for the most part, that pattern held true until about 2009 or 10. That is when AM station’s programming began to be simulcast again (everything old is new again) on FM stations and HD-2 subchannels. It would be interesting to examine why this is so and what it means to the radio business as a whole.

The general trend in the music industry has also been down. This is important because record labels and the radio business used to go hand in hand. Record labels had the job of separating the wheat from the chaff. Those groups or artists that had the talent would be given recording contracts and airplay. With exposure, they would become more known, sell more recordings, record more songs, etc until they peaked and began to decline. Radio stations prospered under this arrangement because they took on none of the risks while getting huge vast quantities of program material to playback, and charging advertising fees for spaces within that programming.

So far so good.

Then, two things happened:

The communications act of 1996
The Internet

The communications act of 1996 forever changed the way the radio business was run in this country. No longer were there several thousand individual stations, the most influential of which resided in markets #1 and #2. Instead, there were conglomerations of stations run out of Atlanta, Fort Worth, and a dozen or so other medium-sized cities. No longer were stations competing head to head and trying to be the best and serve their respective audiences; rather, station A was positioned against station B to erode some of its audience so that station C could get better national buys from big ad agencies. No longer would possible controversial artists like the Indigo Girls get airplay on some groups. Songs were sanitized against possible FCC indecency sanctions, morning shows became bland and safe, and radio on the whole became a lot less edgy as big corporate attorneys put the clamps on anything that would invite unwanted exposure.

The last great musical genre was the Grunge/Seattle Sound of the early 1990s. Those bands somehow mixed heavy metal, obscure mumbled lyrics, flannel shirts, and ripped jeans into something that the dissatisfied Gen Xers could understand and appreciate. By 1996, this had morphed into “Modern Rock,” and carried on for several years after that, to fade out in the early 00’s. Since that time, there have been no great musical innovations, at least on the creative side, other than the ubiquitous Apple computer and Pro Sound Tools software.

The internet greatly changed the way recording labels did business, mainly by eating into their bottom line. This had the effect of circling the wagons and throwing up a protective barrier against almost all innovations. The net result was fewer and fewer talented artists being able to record, which pushed those people into smaller, sometimes home-based recording studios. While those studios can put out good or sometimes even excellent material, often the recordings lack the professional touches that a highly trained recording engineer can add. Add to this the mass input of the internet and no longer are bands or artists pre-screened. Some may point to that as a good development with more variety available for the average person. Perhaps, but the average person does not have time to go through and find good music to download from the iTunes store. Thus, a break developed in the method of getting good, talented artists needed exposure. Youtube has become one of the places to find new music, but it is still a chore to wade through all the selections.

Thus, when FM HD-2 channels came into being, there was little new programming to be put into play. HD radio was left to broadcast existing material with reduced coverage and quality than that of analog FM. That trend continues today where now analog FM channels are being used to broadcast the news/talk programming that used to reign on AM.

What will happen next? If Tim Westergren has any say, the internet (namely Pandora) will take over and terrestrial radio will cease to exist. Current trends point solidly in that direction, although I think Tim is a little ahead of himself in his prediction.

News/Talk on the FM dial point not to an attempt to shift the wheezing, white, (C)onservative/(R)epublican programming to a younger demographic, who will, if I am any judge of history, remain unimpressed. No, rather, they are running out of other source material, simulcasting syndicated talk radio is cheap, lean, and a good way to make money without having to pay actual salaries.

What is “Phasing” as it relates to radio?

Occasional reader Jeffery asks a good question, which I will attempt to answer here in simple terms. Phasing, when used with antennas, refers to the relationship that two or more radiating elements share with the waveform being transmitted. It is used to create an RF radiation pattern by adding energy to the wavefront in one direction by taking energy away from the wavefront in another direction.

Phasing is often described as +/- X number of degrees from a reference point. Graphically, it would look like this:

One wavelength with +/- 180 degrees notated

The reference point can be changed to any point on the waveform, in radio applications it is usually oriented around +/- 180 degrees. If the reference point is a single tower or element then this would be the end of the story. Add a second tower to this system and it would look something like this:

In this picture we have two waves being radiated from two separate elements. These elements are spaced 100 degrees apart and tower #2 is phased to +90 degrees. RF generator is coupled to both towers via a power divider, the reference tower (tower #1) is feed with 57% of the power that tower #2 is being feed. Thus, the ratio of power to the respective towers would be 57:42. Thus, if tower one had a power reading of 1.00, tower two would be 0.74. The towers are on a north/south line with the reference tower bearing 180° from tower #2. In the area of subtraction, the waveforms from each tower cancel each other out to some radiating less power toward the south; in the area of addition, the waveforms sum to create a more powerful waveform, radiating more power towards the north.

Resulting pattern (WKIP, Poughkeepsie, NY):

This is a typical two tower array, however, there are two slight differences; the reference tower is 215 degrees tall, tower two is 90 degrees tall. This is yet another use of “degrees” to relate electrical length or separations. The second, more notable distinction is that this array is Directional daytime, and non-directional night time, which is the opposite of most AM stations in this country.

Electrical height can also be described as a function of wave length, e.g. 1/4 wave, 1/2 wave, etc. Most AM towers in this country are 1/4 wave length, which equates to 90 degrees. Often, higher powered stations, and some low powered stations put up towers near 1/2 wavelength due to the better ground wave performance of those towers. At lower dial positions, a 1/2 wave tower becomes an expensive proposition due to the height required.

In theory, an unlimited number of towers can be used to create a pattern by introducing nulls (areas of subtraction) and lobes (areas of addition). In practice, the highest number of towers I’ve ever heard being used in an AM directional array is twelve; KFXR 1190, Dallas, TX. There may be others, too.

An excellent resource for AM directional antenna technical information is Jack Layton’s Directional Antennas Made Simple, which is out of print but available from various sources.

AM radio sucks! It’s horrible, sounds terrible and should be turned off!

This is a youtube video of a Police song from the 1980s received via skywave and recorded off-air on an AM radio.

Video Description:

The classic 1983 #1 smash hit, as received in analog C-Quam AM Stereo… in Japan… via nighttime skywave in the Tokyo area, roughly 500 miles away from Sapporo (ed: where the station is located). The audio quality is among the best I’ve ever heard from analog AM radio, thanks in large part to an excellent wideband receiver, very quiet band conditions, and the Orban Optimod-AM 9100 audio processor being used by HBC Radio to its maximum extent: 12.5 kHz audio bandwidth with stereo enhancement added (above and beyond the amount naturally provided by the matrix processing used by AM Stereo).

Absolute trash, I tell you. Just awful.

Of course, I know several FM stations around here that wished they sounded as good. Naturally, Japan, they have sought to minimize night-time interference problems by limiting the number of stations on the air and enforcing the rules and regulations in place to protect those stations on the air. They also seem to allow greater bandwidth, out to 12.5 KHz in spite of the narrower channel allocations (9 KHz in ITU regions I and III, vs 10 KHz here in the US, ITU region II). One other thing to note, there is no digital buzz saw occupying several channels of the broadcast spectrum. Keep in mind, this was received in Tokyo, likely a very high noise environment.

I was trying to find out the power level of the transmitter, the call sign is JOHR in Sapporo Japan, frequency is 1287 KHz. HBC is the Hokkaido Broadcasting Company, a privately held company. The state-run radio outlets in Japan are NHK, which has several radio and TV stations throughout the islands.

Anyway, AM is dead. Killed by the very owners of the broadcasting companies themselves with help from the NAB. They are the ones that petitioned the FCC to loosen up the allocations and allow more and more stations to be crammed into the band. That is old news. The new news is same forces that killed AM radio are diligently working their magic on the FM band as well. More stations, translators, digital IBOC nonsense that doesn’t work, more of everything. After all, more is better. Until it is not. Then it’s too late.