Radio notes, by Karl Shoemaker

Definitions and Acronyms

Communication: Method to transfer human intelligence 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: Method 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 Hertz, and multiples of. Typical frequencies are in KHz, MHz or GHz. A "standard" radio frequency could be called a "channel". A channel is an easy term for non-technical operators (such as CB) to select on a radio console. Military, technical and Amateur operators prefer 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 underwater communication 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. Upper 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 varying from a few inches to many miles. Normally, information (intelligence) 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 modulation. Information (intelligence) such as voice, data, or images that modulate the Tx carrier to be sent out. In the case of voice the carrier is modulated at an audio rate.

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

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

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

PE: Pre emphasis. Tx audio response is increased at the audio high end. PM Tx has natural (uncontrolled) PE, whereas FM Tx does not. The latter has circuits to duplicate PM to be compatible with Rx deemphasis. Typical LMR is 6 db per octave 300 Hz to 3 KHz audio information (intelligence).

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 understandability of the receiving operator to hear and understand traffic. PE and DE can help accomplish this.

DMS: Deviation Maximum Setting; The maximum 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) sensitivity for an average of radio operators voice strength 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 misunderstood and misused by LMR-FM system radio operators and design engineers in both professional and Amateur design, operation and maintenance today.

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

RSL: Received Signal Level: RF level into a receiver, expressed logarithmically, in "dbm". Typical signal levels in LMR is around -100 to -50 dbm. Typical signal levels in point to point microwave systems is -50 to -30 dbm. RSL typically is measured at the TOR.

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 noise in the absence of radio traffic (signals). With FM systems this is intolerable for the operator to listen to, for more an a few seconds. A squelch 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 absence 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 variable from 0~1 second depending on receiver quieting.

Full Quieting: A distant signal so strong into a receiver there is no (noticeable) 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, whereas, 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 condition by changing the DC voltage. 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 equivalent of COR and became an alternative term in the solid-state era. Either acronym is used, depending on which manufacture is used for equipment.

CTCSS: Continuous Tone Code Squelch System. The universal term used to describe 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 transmit 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 arrangement, 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 useful in commercial CTCSS stations and compatible 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 lifted out of the HUB when the operator is attempting 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 description 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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