Some Basic Definitions
The following terms appear in Dan
Slentz’s eBook article about building an LPFM. They are explained in only basic
terms here for readers who may not be familiar with them. Detailed definitions
can be found via numerous online resources.
TECH RACK TERMS
AoIP or Audio over Internet
Protocol — Similar to VoIP (Voice over Internet
Protocol in telephone systems), Audio over Internet Protocol is the latest in
audio board technologies, where digital uncompressed audio is delivery over a
single Cat-5e/6 cable between studios and gear. The audio characteristics are
of full CD quality and noise/interference are better rejected by twisted pair
audio than traditional wiring. Additionally (and unlike AES digital audio or
balanced analog audio), control of equipment can be made through the AoIP
interface, and cable and connectors (RJ-45) are both less expensive than
Cat-5e / Cat-6 — This is the cabling use for computer connections
(including AoIP). Cat-5 is the older standard that is steadily being replace by
Cat-5e and/or Cat-6. Though 5e or 6 cable can be used for video (with the use
of baluns) or telephone, it’s most frequently used in computer connections or
— The ability to give a phone caller who is on-the-air the sound out of the
audio console (the “mix) minus their own voice (the “minus”). Without
this ability, you would create a “loop of sound” (callers voice to board to
caller to board to caller… etc.) creating a feedback loop.
Remote Broadcasts — Having a
remote audio origination point other than your studio. This could be coverage
of a high school football game to a broadcast from an event like a county fair
RJ-12, R-J45 — These are the “Registered Jacks” for phone and computer. The
RJ-11 and RJ-12 (4 and 6 wire) are typically used for telephone connections
while the RJ-45 (8 wire) is typically used for connecting computers and in AoIP
or Remote Production Unit (or Radio Propagation or Programming Unit) — This
is a system for remote broadcasting where a wireless transmitter (licensed)
sends audio back to the station for live remote broadcasting. Over the past
years, this gear has often been replaced with cell phone technology, streaming,
and digital audio interfaces (or a combination)
STL or Studio to Transmitter Link — A
system, traditionally licensed over-the-air wireless, used to get audio from
your studio to remote transmitter location
Stream Encoder/Decoder — Instead of
traditional STLs, many stations have gone to digital stream encoders using
wireless systems and wired broadband (like DSL or cable modem) to get their
audio from the studio to transmitter site, plus to remotely control the
transmitter site gear.
TSL or Transmitter to Studio Link — Sometimes it is necessary to
get return audio to the station from the transmitter site (for instance, when
you have a RPU unit on your tower), this traditionally was another piece of
TRANSMITTER CHAIN TERMS
or FM Transmitting Antenna — This is the entire fixture that
makes up your antenna. It could consist of one or many “bays.” Each bay adds to
the antenna’s effectiveness in extending signal reach.
Audio Logger — A piece of gear (from
tape-based cassette to digital recorder) used for recording your on-air
programming. It can be used to prove (if questioned about content later) what
was played or said on the air. The logger can be set-up to just record times
when the microphone is open (turned on), or all audio. Typically the logger
audio quality (when recording ALL content) is a lower-resolution version so it
doesn’t use up as much hard drive space.
Bay or Antenna Bay — In reference to an antenna, this
is one of the “elements” or parts that make up the entire antenna. The antenna
could have a single bay (which looks like a V-shaped pipe, a T-shaped pipe, or
a C-shape with a twist pipe), or it could have numerous bays. The more bays,
the more gain, plus greater cost and heavier weight on the tower. But the more
bays, the less power (TPO) your transmitter will need to put out to hit your
effective radiated power (ERP)
Back-up Audio Source — For any number of reasons, your transmitter
could lose the incoming audio (even if the transmitter is located at your
station). Power could go out in your studio. Your automation could fail. The
audio board power supply could go out. And for a remotely located transmitter,
losing your STL or audio stream to the transmitter is always a possibility.
When this happens, there is equipment that can quickly replace that lost audio
with “back-up audio”. Some transmitters now include internal audio players for
loss of incoming audio.
Coax — Line carrying the signal from your transmitter to antenna. Minimum
for an LPFM would be half-inch (diameter); the smaller the size, the more line
loss but the lower the cost.
EAS / CAP or Emergency Alert System & Common Alerting Protocol —
LPFMs are required only to have the decoder in place for rebroadcast of
emergency alert announcements.
ERP or Effective Radiate Power — The power with which the station is
authorized to broadcast. This is NOT the transmitter power, rather the power
that is generated when you factor in additional elements such as line loss,
antenna gain and height above average terrain (HAAT).
FCC or Federal Communications
Commission — The government agency that oversees broadcasting and
electronic communication. At the direction of Congress, it set out the rules
and system that allowed the expansion of the LPFM service.
Fold Back — Expression to
indicate a transmitter is lowering its power automatically. This is done if it
sees a high VSWR or there is another problem affecting the transmitter.
HAAT or Height Above
Average Terrain — This is the center of our antenna above the average
terrain. This is not simply where the antenna sits in relation to the ground
below the tower, but the height above the terrain when it is averaged for the
Loss — The amount of power or signal your coax cable loses naturally over
the length of the cable being used.
LPFM — Low-power FM is a “community class” of broadcaster.
Currently LPFMs are licensed with an ERP of 100 watts. A prospect for even a
lower (10 watt) version is apparently no longer being considered, though a
higher-power version (LPFM 250) at 250 watts has been debated.
kW or Kilowatt — A
measurement of power. For instance, in radio a transmitter that is 1,000 Watts
can also be said to operate at 1 kW. The prefix “kilo” means one thousand.
Line Loss — The
amount of power or signal your coax cable loses naturally over the length of
the cable being used.
RDS or RBDS or Radio Broadcast
Data Service — This is auxiliary data that your transmitter can put out
(via a subcarrier or “SCA”) that includes program information accessible by new
RBDS equipped radios. That data might include your format, song title and
artist, and other information. It can be as simple as a static display of your
call letters and slog, or more involved with data that changes.
RF or Radio Frequency —
This is the invisible power through the air that IS the signal that the
consumer’s antenna received that carries our signal.
RPU or Remote Pickup Unit —
Like the STL, this is the expression for the licensed gear
(transmitter/receiver) that has frequently been used for “live remote
broadcasting.” The traditional radio RPU required a special radio (in a van or
portable), antenna, line-of-site between the remote transmitter and receiving
system (usually on a tower at the station or on the station’s main broadcast
tower. The audio from the RPU would then be fed to the on-air console. These
could be used for news, sports programming, or any place from where the station
wanted to do a remote broadcast. More recently traditional RPUs have been
replaced by stream encoders and cellular systems.
SCA, Subcarriers or Subsidiary
Communications Authority — This can be an additional “service” or feature that
you broadcast through your FM transmitter. Services like background music and
reading services for the blind, which rely on specialized radios — as well as
RDS data to display song title/artist on RDS-equipped radios — are generated
via “SCAs.” No special licenses are needed for these services and they allow
for greater audio modulation levels on your primary service (see above) up to
110 percent modulation.
STL or Studio to Transmitter Link — When a transmitter is located at
an area away from the studio, the traditional piece of equipment that
“privately” sends your signal from the studio to transmitter is referred to as
the station’s STL. These can be expensive and require special licensing.
Stations now sometimes use special private stream encoding systems in place of
or Total Power Output — The actual power that transmitter is emitting. If
measured, this would be directly at the output of the transmitter. This is NOT
the power we are licensed for, rather the power the transmitter must operate to
reach our licensed power, which is called ERP, or Effective Radiated Power.
VSWR / VSR or Variable
Standing Wave Ratio — The amount of power reflected back into the
transmitter either by natural elements like freezing rain or by antenna or coax
failure. VSWR can be damaging to the transmitter.
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