Online LPFM Radio Resource: LPFMRadio.com
Technical Pictures
As with the studio equipment, these pictures are representative of a "mid-budget" LPFM station. That is, one which is built around some "new" equipment but doesn't shy away from some of the better and well maintained "experienced" pieces of equipment. These pictures are examples of what you may choose to do.
Soon, we'll be building several different configurations of the LP-100 class station. we'll photograph and document each and every step of the way for you to see.
At the top of the processing rack is the new DB Max processor (by TC Electronics). This is, currently, used to process (barely) audio in the production chain.
Immediately below is an Aphex Aural Exciter, type III. This is extremely useful for enhancing highs and lows .
Next down is the Belar AM modulation monitor. This photo was taken during construction of the AM antenna.
The next three devices are Harris MSP-90 tri-band AGC-Compressors. The upper and lower of the three are used as "pre-processors" which feed the Optimod 8100 unit (below). these are required, as the Optimod utilizes a "neural network" add-in card. The center MSP-90 "pre-processes" the mono-only output of the audio console. This is fed into the AM processors (which you'll see a little later on).
The fourth (and last) Harris MSP-90 unit is a single band compressor and peak limiter. These are used as a "noise gate, compressor, limiter" to clean-up external feeds on an "as needed" basis. Most use involves clean-up of National Weather Service audio for EAS use.
The Orban Optimod 8100 is the final audio processor used in the audio chain. The only processing to follow this is the composite clipper. The Optimod is set up strictly as a slow AGC followed by a multiband compressor (the six band limiter, XT chassis, just below). The stereo generator is an integral part of the Optimod.
Directly below the Optimod is a Symetrix 528E microphone processor. This is used as studio equipment and is explained in that section.
Below the Symetrix 528E is an Eventide Harmonizer. This, too, is used as studio equipment and is explained in that section.
Below the Eventide Harmonizer is the Sage/Endec EAS system. Ours is set up with two remote relay panels, giving us the ability to separately control FIVE stations at once.
Below the Sage/Endec is a patch panel an audio distribution amplifier, a reverb, a telephone hybrid, and several receivers which feed signals into the Sage/Endec for EAS monitoring.
Here is a look at the FM modulation monitor. Directly beneath it, you can see the AM multiband limiters (Inovonics MAP II's). The MSP 90 (pictured above) pre-processes the mono (temporarily) AM audio. It is then fed into the top Inovonics MAP II for further processing. It is then sent to the bottom Inovonics MAP II and is fairly "flat" (as far as levels are concerned) by this time. The output of the second MAP II is fed into the Inovonics 222 and further processed (limited, pre emphasis added, "brick-wall" filtered) as required to insure NRSC compliance. This combination can actually modulate the AM transmitter at upwards of 150% positive and still keep negative peaks at or below 100%.
Click on the tower picture for more on the FM antenna design.
More pictures (the actual transmitters, both main and backup) will be added soon.
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Below, is some technical information pertaining to our stations. |
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| When any
low power transmitter is operated the range of transmission will be dramatically reduced
in comparison to full power broadcast stations. This is due to the fact that signals
in the FM band do not easily pass through walls of buildings. Concrete,
metal, stucco and brick are major obstacles. Signals will however pass through glass with
little attenuation. This is how signals from high powered commercial stations get in
to your house. A good analogy would be sunlight. Even a room with only a single small
window will have some amount of illumination throughout. Likewise, there will usually be
sufficient signal from high powered stations streaming in your windows (either directly
from the transmitting antenna or reflected) to produce a fully quieted signal.
Low power FM transmitters rather than being like sunlight are more like a streetlight. To get maximum legal coverage, your transmitter has to be outside. Some manufacturers and distributors are recommending external antennas, intended for connection to an inside mounted transmitter. Based on current FCC rules, THIS IS (UNKNOWN TO LOTS OF PEOPLE) TOTALLY ILLEGAL! FCC regulations are quite explicit, requiring that no modifications be made to the original antenna supplied with the product. |
You ARE, however, allowed to operate multiple, FCC certified, micropower transmitters. So ours is designed to be mounted outside, kind of like a PA speaker. When additional coverage is required, we can simply add more transmitters. All transmitters are set to the same frequency, and all carry the same audio simultaneously. A listener moving through our coverage area will not notice the change from one transmitting cell to the next. |
