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Page history last edited by PBworks 12 years, 9 months ago

DAB And Future LPAM Possibilities


The future of AM Broadcasting will include digital modes of modulation. And modulation is what it is, utilizing the circuitry of the quadrature sampling detector. A circuit that is used both in the listeners radio receiver and the broadcast transmitter.


The QSD circuit as it is called when used in the transmitter is referred to as the quadrature phase modulator. It allows for phase modulation of the side bands to create such things as standard Amplitude Modulation. Single Side Band and FM.


The advantage for AM uses is that the modulation is prepared in software and the characteristics of the modulation are what you might refer to as precision. Precision in terms of audio bandwidth and filtering as well as amplitude. Precision such as you can not get by pressing a few buttons and turning a few knobs on standard sort of transmitters.


This method of modulation also makes possible C QAM for AM stereo which is not exactly a new mode but will be a revived mode under the use of digital quadrature phase shifted modulation. Which is sort of a future transition in radio that is coming.


The QSD Stage also makes possible such digital or DAB modes as IBOC and DRM. However IBOC tends to be very wide banded and results in adjacent channel interference. DRM (Digital Radio Mondiale) on the other hand tends to be more efficient and keeps its channel energy in the channel and out of the adjacent channels. A station in Germany operates on 4.000 Mhz with its lower half of the channel in the 80 meter band from 3.995 to 4.000 MHz. Not exactly where anyone would want them to operate. However the ham radio operators operate to within a 200 hertz of the that signal on sideband and do not suffer adjacent channel interference. Some good methods exist for DAB modes, DRM being the better one. (IBOC on the other hand tends to defy the concept of keeping the bandwidth clean and free of adjacent channel interference. It is suspected that IBOC needs to be redesigned or retired for a better method. DRM comes in versions such as the Ham Radio version with even less channel width used. So DRM is more than feasible and hence more preferred, tried and tested.)


The thing is, most people do not want to see allot of high powered digital stations using up the bandwidth on Medium Wave. However LPAM stations in the future sometime can utilize such methods and not have the Medium Wave band filled with such stations in high powered terms. In this regards only DRM should be utilized because it is the preferred method that does not have the problem that IBOC has. Currently on the Internet there is a battle waging over IBOC and it's problem with it's band energy extending out of the channel.


Now I should make a comment about the notion that some say the Medium Wave Band is dead unless they can make it sound like FM stereo via digital broadcasting. Well this is not true. The vision of the people who want DAB is the vision of having text and graphical content even mini web sites being broadcast along with the digital audio stream over the airwaves. DRM is this way, I have seen mini web site pages on my Multimedia Content Window coming along in the airwaves with the audio. So it is about commercial advertising applications more than anything. Putting graphics of products or of concerts and ticket sales in the Multimedia Content Window.


If you listen to the Medium Wave Band at nighttime you will soon realize that the standard Medium Wave Band with it's Amplitude Modulation is far from dead. It is full of life.


Digital radio broadcasting on the Medium Wave band seems to be something more suited for a possible future use in LPAM. This comment at this time however is not about authorizing DAB for use in LPAM at this time. It is left open here for possible use in time. However I would excluded IBOC from the line up for possible LPAM uses since it is technically a problem and the problem that IBOC has needs to be resolved.

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