Definitions and Acronyms

Communication: Method to transfer human intellegence from one person to another. In some isolated cases to non-human beings.

LMR: Land Mobile Radio; generally used for all 2-way radio system on land/earth operation for police, fire, government and Amateur Radio communications. This excludes broadcast, point to point, aircraft and earth to space microwave communications.

Radio: Meathod of communication using electromagnetic signals sent over the air waves. In some cases in the ground or water. Most of this document will only cover analog communication.

Frequency: Referred to a radio frequency expressed in Herts, and multiples of. Typical frequencies are in KHz, MHz or GHz. A "standard" radio frequency could be be called a "channel". A channel is an easy term for non-technicle operators (such as CB) to select on a radio console. Military, techicle and Amateur operators perfer to use the term "frequency".

RF: Radio Frequency. Frequency and bands use for radio communications. Older term is "wireless".

There are many frequencies/channels in bands, which include:

ELF: Extremely Low Frequency: 3 KHz to 30 KHz. Typical use is unwater commincation for sea mammals and military submarines.

VLF: Very Low Frequency: 30 KHz to 300 KHz. Typical use is submarines and land/water navigation systems.

MF: Medium Frequency; 300 KHz to 3 Mhz. Typical use is AM broadcast in the United States. A broadcast carrier normally stays on all the time of service.

HF: High Frequency; 3 MHz to 30 MHz. Typical use is long range LMR; AM, SSB communication for military, Amateur, citizen band and some foreign AM broadcast. LMR carriers drop out the end of a transmission.

VHF: Very High Frequency; 30 MHz to 300 MHz Typical use is aircraft, LMR, AKA 2-way, for military, government and Amateur.

UHF: Ultra High Frequency; 300 MHz to 3 GHz. Typical use is as above, plus microwave systems, both for point to point earth and earth to (space) satellite, including television relay and distribution.

SHF: Super High Frequency: 3GHz to 30 GHz; Mainly for point to point microwave systems and earth to (space) satellite links.

EHF: Extremely High Frequency: 30 GHz to 300 GHz. Uppper end of the radio frequency bands, below the light wave bands.

Tx: A transmit path or transmitter capable of putting out an electromagnetic (carrier) wave for distances varing from a few inches to many miles. Normally, information (intellgence) is applied to the Tx carrier going out.

Rx: A receive path or receiver capable of picking up the above Tx signals and turning them into information that can be understood, such as audio, data or images.

AM: Amplitude moduation. Information (intelligence) such as voice, data, or images that modulate the Tx carrier to be sentout. In the case of voice the carrier is modulated at an audio rate.

FM: Frequency Modulation. Similair to above, except the frequency changes instead of amplitude. In FM, the fundlemental Tx carrier frequency changes at the rate of intellegence needed. In the case of voice LMR systems the carrier is modulated at an audio rate.

PM: Phase modulation. Similair to FM, howver, the phase of a carrier is modulated. This mode has audio frequency response issues, whereis, FM does not.

MI: Modulation Index: The ratio of audio rate of an FM carrier to be sent out, typcially affecting LMR and broadcast systems. MI changes enharently with PM where it does not with FM.

PE: Preemphasis. Tx audio response is increased at the audio high end. PM Tx has natural (uncntrolled) PE, whereis FM Tx does not. The latter has circuits to duplicate PM to be compatible with Rx deemphasis. Typical LMR is 6 db per octive 300 Hz to 3 KHz audio information (intellegence).

DE: Deemphais. Rx audio response is decreased at the audio high end. Just the opposite of PE.

SNR: (or S/N) Signal to Noise Ratio. Better SNR results in better understandabliy of the receiving operator to hear and understand traffic. PE and DE can help accomplish this.

DMS: Deviation Maximum Setting; The maximun setting an FM transmitter should be allowed to modulate a carrier. For FM systems, this limits deviation of the RF carrier expressed in KHz. Most Amateur system are 5, where professional systems are migrating to 2.5. Analog broadcast systems are 75 for FM and 25 for TV audio (aural).

MG: Mic Gain. The best microphone (input) sensitivty for an average of radio operators voice strengh and background noise. Optimum mic gain produces an average of 2/3 system modulation, with brief moments of DMS to produce low-distortion and distraction in radio traffic. Both DMS and MG is often misundertood and misused by LMR-FM system radio operators and design engeeners in both professional and Amateur design, operation and maintence today.

TOR: Top Of Rack/ Top Of Radio: Measurement point of RF levels to determine system status or performance.

TTL: Test Tone Level: In the case of audio a reference level of full system modulation between a Tx and Rx.

TLP: Test Level Point: In the case of audio a reference level benchmark of system components. This is a maximum and never exceeded. Operation and testing levels are performed a TTL or lower depending on system design. TTL and TLP typically are expressed in dbm.

Squelch: Receivers out out noise in the absence of radio traffic (signals). With FM systems this is untollable for the operator to listen to, for more an a few seconds. A squlech will mute the receiver's output during no channel activity.

CS: Carrier Squelch. A squelch circuit operated only by a carrier. Used in AM and FM systems.

NOS: Noise Operated Squelch. For FM systems only; the receiver output noise causes the squelch to operate. Channel activity (RF carrier) causes the absense of noise, therefore, opening up the squelch to allow valid traffic (signals) to be heard by the operator.

Noise Burst: The duration from the time a (distant) carrier stops, to the time the squelch closes the receive output. This is normally less than 1 second. In some cases is varible from 0~1 second depending on receiver queiting.

Full Quieting: A distant signal so strong into a receiver there is no (noticable) noise with the (voice) traffic being heard by the operator. In modern FM receivers this is more than -80 dbm TOR.

Scratchy: A "loose" term used by an operator when traffic is much less than "comfortable" listen, whereis, noise is competing with the (intelligent) traffic. In modern FM receivers this is less than -110 dbm TOR.

Breaking up: Another "loose" term used by an operator, when traffic is so weak the receiver starts to squelch out certain words of the traffic being heard.

PTT: Push To Talk; the line that causes a Tx to send out the signal. It's normally controlled by a push button on the microphone of the station; push to talk; release to listen.

RUI: Receiver Unsquelch Indication. For the Micor is a pin output on the audio-squelch board to indicate a receiver unsquelch contion by changing the DC volage. This point can be used to operate other devices.

RUS: Receiver Un Squelch. A further break down of the above acronym, mainly used in G.E. systems.

COR: Carrier Operated Relay; The Rx squelch circuit buffers and converts RUI/RUS to a DC output. This, in turn can operate other devices, such as a repeater's Tx PTT. The word relay came from the old tube days whereas the squelch circuit contain a tube which ran current through a high voltage relay coil.

COS: The same and equilivant of COR and became an alternative term in the solid-state era. Either acronym is used, depending on which manufactor is used for equipment.

CTCSS: Continous Tone Code Squelch System. The universal term used to discribe channel squelch system requiring both carrier and a sub-audible tone to operate. The tone originates in the far end transmitter. The local receiver's (absence of) noise, plus the distance tone opens the receiver squelch.

CCI: Co Channel Interference; Several systems can occupy the same channel, however only one must transmitt at one time. Other systems can be an annoyance to listen to, therefore CTCSS can "ignore" this traffic. There are limitations and problems to this arrangment, however.

PL: Private Line; A Motorola trademark, indicating a radio channel is protected from co-channel traffic, to the fact only the intended traffic is routed to the intended persons/stations. It gives the operator the (ignorant) perception only one system is on a channel.

GC: Channel Guard; GE's version of the above.

CG: Channel Guard; RCA's version of the above.

PLI: Private Line Indicator. Indication of a valid CTCSS being received and decoded. For the Micor audio-squelch board is a pin output to tell an AND squelch how to function. It also can light an indicator on a radio panel to indicate a valid tone is active.

OR squelch: This allows tone to keep a squelch open, even if the carrier goes away, at least for brief periods. Squelch sensitivity is controlled by decode of the valid tone. This is only usful in commercial CTCSS stations and compable mobiles as well.

AND squelch: This requires BOTH carrier and tone to keep a squelch open. This is the better than OR squelch for Amateur operation. Squelch sensitivity is adjustable.

HUB: Hang Up Box: A mobile mic holder containing a switch to sense when the mic is lifed out of the HUB when the operator is attemppting to make a transmission.

CL: Close Loop; the standard for Motorola's PL systems; normal PL mode control is a close loop, going to ground. Opening the loop causes CS receive. In a mobile, the HUB has a switch inside performing this function. On base it's usually a separate button next to the PTT.

OL: Open Loop: The standard for G.E. CG systems. normal CG mode control is a open loop. Closing the loop causes CS receive. In a mobile, the HUB has a switch inside performing this function.

Compa: Motorola's discription of a compact, complete base station, housed in a metal cabinet.

This document may be used for Amateur purposes with the Author given credit for it's content. This document may be printed and passed on to other Amateurs, with the understanding not to modify or change the content of the document without the Author's permission. Notifications of typos or errors are welcome.

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