Talk:Two-way radio

Radiotelephone
Is "radiotelephone" the British English word for two-way radio? User:David Jordan 10/02/2006.

I'm pulling the flag to merge the articles because there is not a solid case for both terms meaning the same thing. User:David Jordan 11/30/2006.

Here's one idea of how articles could fall under Two-way radio category. Comment on why this doesn't work below. Talk:David Jordan

Cleanup needed
The frequency-response figure is baffling. There's too much specialized jargon too early in the article. Organization is poor (talk about conventional *before* trunked, clearer that way and the motivation for trunking becomes easier to explain). How about some *H*I*S*T*O*R*Y, darn it? The first two-way system applied to police cars was in the US in the '20s, I think...got to find more. If someone wants to read about FRS or GMRS or other services there's LINKs to follow - we don't need to beat this to death here. I'm putting this one on my to-do list. --Wtshymanski 23:12, 30 November 2006 (UTC)

February 2007 Merge discussion
Can anyone please explain why Walkie-talkie and Two-way radio have distinct articles when they both seem to describe the same technology? It is my opinion that is is redundant, confusing, and that content from the walkie-talkie article be merged to two-way radio article.--Kevin586 18:56, 26 February 2007 (UTC)

Oppose. Distinct topics, "walkie talkie" is a historical two-way radio system as well as being modern jargon for a hand-held transciever. There can be a lot of depth to the WT article that would be too much for a more general two-way radio article. Two-way radio systems also include fixed (base station), and vehicular equipment. If we can have individual Pokemon articles, we surely can afford to have "walkie talkie" as a separate article. --Wtshymanski 19:00, 26 February 2007 (UTC)

Oppose I agree with wtshymanski 's point and add that the "walkie talkie" is a distinct part of the culture, being the way that many events and firms communicated before the advent of cell Phones. Indeed early cell phones were a logical extension of the walkie talkie concept. Two way radio far predates the technology that allowed a hand held (or even AN/PRC style backback) unit. Early 2 way instalations had several chassis and a Dynamotor all mounted in the trunk of the vehicle.cmacd 13:39, 27 February 2007 (UTC)

The Two Way Radio article has 22,000 characters. This approaches the maximum limit before it needs to be broken into a separate article. Oppose. 146.74.231.245 23:54, 27 February 2007 (UTC)

Between 50 and 100 articles link to Two-way radio and Walkie-Talkie. Some overlap but there are differences. They're not the same thing, in my opinion. 03-02-2007 User:David Jordan

First
I've learned never to call anything on Wikipedia the "first" but can anyone give me a reference for the anon addition which I've just moved here: ''In 1930 the first three cities debuted two-way police radios. The Pasadena, Berkley, and Tulare Police Departments added police band radios. These were licensed as KSW 2410kc and WPDA 1712 kc.'' This isn't what the IEEE milestones site says, though they refer to "high frequency". These two frequencies would be called "medium wave" or medium frequency. --Wtshymanski 17:56, 2 October 2007 (UTC)

One might note, too that the Wikipedia page for the Detroit Police Department credits them with the first two-way car radios (http://en.wikipedia.org/wiki/Detroit_Police_Department); the author got his information at http://www.michmarkers.com/startup.asp?startpage=S0529a.htm. I'm a little dubious about the Australian claim... — Preceding unsigned comment added by Ejdamer (talk • contribs) 00:43, 6 April 2013 (UTC)

In Practice?
This article is very informative on the technical side. As a lay person with an interest in how schools could use 2-way radios in day-to-day operations as well as in communicating with first responders in an emergency (i.e., when an active shooter is on the premises), I was hoping an article on Wikipedia would include a section that focuses on the human side of using 2-way radios. How do you "get the hang of it?" Why use 2-way radios if we all have cell phones? How does the technology shape the communication experience between or among the users? Does it shape what to say, how to say it, when to say it?

Also, I'm interested in interoperability issues and just how seriously they're taken. For instance, here in Colorado, when first responders from different agencies arrived on the scene at Columbine during the student shooting rampage, they were unable to communicate with one another, and this caused considerable confusion related to chain of command. I'm finding out in my private discussions that many schools using 2-way radios can only afford units that come nowhere near the sophistication of the 2-way radios used by professional law enforcement, firefighters and other responders. As a result the schools' systems cannot communicate with first responders arriving on the scene for any emergency.

In addition, the lack of interoperability seems to go hand-in-hand with the human use of the 2-way radios in the school system. Schools may develop their own codes or jargon that cannot be understood by professional responders. Slowly, schools are being required to follow National Incident Management System guidelines or become NIMS-compliant, which means they must follow Incident Command System (ICS) doctrine. ICS includes rules on the use of "clear text" instead of any jargon at all. So this brings us back to the topic of The Human Side of 2-Way Radios -- namely, what part does the technology play in building a team or a community?

Any suggestions on whether to include this in the general article? Thank you for your comments.

12.42.161.3 (talk) 16:35, 12 January 2008 (UTC)

UHF vs VHF
Its worth mentioning that in the Northern Ireland "Troubles" the British army radios upset the ROI TV signal, so people knew when a raid was coming. This was a major issue at the time. — Preceding unsigned comment added by 134.36.121.12 (talk) 12:32, 14 June 2011 (UTC)

Alternatives
Please include VoIP over Wifi/WiMax as a alternative see http://www.webopedia.com/DidYouKnow/Internet/2005/voIP_WiFi.asp —Preceding unsigned comment added by 81.246.175.36 (talk) 09:57, 2 March 2009 (UTC)

History of hand-helds
I'd like to read in the article more about the history of hand-helds. Can someone savvy add that with dates? Thanks! (Btw, Is there also a Suggestion section here?) Misty MH (talk) 21:20, 19 September 2012 (UTC)
 * There's a lot of history (continually edit-warred, so you know you're getting the very best information) at Walkie-talkie. If it doesn't have a link here, I'll add one. --Wtshymanski (talk) 15:39, 20 September 2012 (UTC)

Aircraft use
I came here to find out when radios in aircraft became practical. In the History section we're told that they did, but not when. The previous para refers to vehicle use in 1923, and the following para refers to 1933. Some more info needed here, pleaseDean1954 (talk) 08:19, 19 June 2020 (UTC)
 * Radio was first used in aircraft just prior to World War 1, first zeppelins then in the biplane. Civilian zeppelins had radio first (they trailed a wire antenna called a "zepp") but the war really sparked development of light radio sets that could be carried by heavier than air craft.  The first radio transmission from an airplane was August 1910, I think by the US Navy. The first aircraft radios transmitted by radiotelegraphy, so they required 2 seat aircraft with a 2nd crewman to tap on a telegraph key to spell out messages by Morse code.  During World War 1 AM voice two way radio sets were made possible by the development of the triode vacuum tube, allowing the pilot in a single seat aircraft to use the radio.  Here's a timeline of the first experiments in aviation radio.  This info should probably be in one of the aviation articles, maybe Avionics. --ChetvornoTALK 14:43, 19 June 2020 (UTC)

Uncited material in need of citations
I am moving the following uncited material here until it can be properly supported with inline citations of reliable, secondary sources, per WP:V, WP:NOR, WP:CS, WP:NOR, WP:IRS, WP:PSTS, et al. This diff shows where it was in the article. Nightscream (talk) 15:38, 27 August 2022 (UTC)

LEDE SECTION
Two-way radios are available in stationary (base station), mobile (installed in vehicles), and hand-held portable models. Hand-held two-way radios are often called walkie-talkies, handie-talkies or hand-helds. Two-way radios are used by groups of geographically separated people who need to keep in continuous voice communication, such as aircraft pilots and air traffic controllers, ship captains and harbormasters, emergency services personnel like firefighters, police officers, and ambulance paramedics, taxi and delivery services, soldiers and military units, fast food and warehouse employees, and radio amateurs.

A cell phone is an example of a full-duplex two-way radio. During a phone call, the phone communicates with the cell tower over two radio channels; an incoming one to carry the remote party's voice to the user, and an outgoing one to carry the user's voice to the remote party.

History
Installation of receivers and transmitters at the same fixed location allowed exchange of messages wirelessly. As early as 1907, two-way telegraphy traffic across the Atlantic Ocean was commercially available. By 1912, commercial and military ships carried both transmitters and receivers, allowing two-way communication in close to real-time with a ship that was out of sight of land.

As radio equipment became more powerful, compact, and easier to use, smaller vehicles had two-way radio communication equipment installed. Installation of radio equipment in aircraft allowed scouts to report back observations in real-time, not requiring the pilot to drop messages to troops on the ground below or to land and make a personal report.

During World War II walkie-talkie hand-held radio transceivers were extensively used by air and ground troops, both by the Allies and the Axis.

Early two-way schemes allowed only one station to transmit at a time while others listened since all signals were on the same radio frequency – this was called "simplex" mode. Code and voice operations required a simple communication protocol to allow all stations to cooperate in using the single radio channel so that one station's transmissions were not obscured by another's. By using receivers and transmitters tuned to different frequencies and solving the problems introduced by operation of a receiver immediately next to a transmitter, simultaneous transmission and reception was possible at each end of a radio link, in so-called "full duplex" mode.

The first radio systems could not transmit voice. This required training of operators in use of Morse code. On a ship, the radio operating officers (sometimes shortened to "radio officers") typically had no other duties than handling radio messages. When voice transmission became possible, dedicated operators were no longer required and two-way radio use became more common. Today's two-way mobile radio equipment is nearly as simple to use as a household telephone, from the point of view of operating personnel, thereby making two-way communications a useful tool in a wide range of personal, commercial and military roles.

Conventional
Conventional radios operate on fixed RF channels. In the case of radios with multiple channels, they operate on one channel at a time. The proper channel is selected by a user. The user operates a channel selector (dial or buttons) on the radio control panel to pick the appropriate channel.

A channel may be reserved for a specific function or for a geographic area. In a functional channel system, one channel may allow City of Springfield road repair crews to talk to the City of Springfield's road maintenance office. A second channel may allow road repair crews to communicate with state highway department crews.

In a wide-area or geographic system, a taxi company may use one channel to communicate in the Boston, Massachusetts area and a second channel when taxis are in Providence, Rhode Island. This is referred to as Multisite operation. In this case, the driver or the radio must switch channels to maintain coverage when transitioning between each area. Most modern conventional digital radios and systems (i.e., NXDN and DMR) are capable of automatic "roaming" where the radio automatically switches channels on a dynamic basis. The radio accomplishes this based on the received signal strength of the radio repeater's recurring "beacon" signal and a "site" or "roam" list that identifies available geographic channels. Some analog conventional systems can be equipped with a feature called "vote-scan" that provides more limited roaming (rarely used in practice). Radio "simulcast" technology can also be used in adjacent areas, where each site is equipped with the same channel. Here, the transmitters must be closely synchronized, and a centralized voter or receiver comparator device is required to select the best quality signal from the mobile radio. This is often used in public safety and utility radio systems.

In marine radio operations, one channel is used as an emergency and calling channel, so that stations may make contact before moving to a separate working channel for continued communication.

Motorola uses the term mode to refer to channels on some conventional two-way radio models. In this use, a mode consists of a radio frequency channel and all channel-dependent options such as selective calling, channel scanning, power level, and more.

Scanning in conventional radios
Some conventional radios scan more than one channel. That is, the receiver searches more than one channel for a valid transmission. A valid transmission may be a radio channel with any signal or a combination of a radio channel with a specific Continuous Tone-Coded Squelch System (CTCSS) (or selective calling) code.

There are a wide variety of scan configurations that vary from one system to another. Some radios have scan features that receive the primary selected channel at full volume and other channels in a scan list at reduced volume. This helps the user distinguish between the primary channel and others without looking at the radio control panel. An overview:


 * A scanning feature can be defined and preset: when in scanning mode, a predetermined set of channels is scanned. Channels are not changeable by the radio user.
 * Some radios allow an option for user-selected scan: this allows either lockout of pre-selected channels or adding channels to a scan list by the operator. The radio may revert to a default scan list each time it is powered off or may permanently store the most recent changes. In professional radios, scan features are programmable and have many options. Scan features can affect system latency. If the radio has a twenty-channel scan list and some channels have CTCSS, it can take several seconds to search the entire list. The radio must stop on each channel with a signal and check for a valid CTCSS before resuming scanning. This can cause missed messages.

No delay from user push-to-talk until the user's voice is heard in the radio's speaker is an unattainable ideal.

Talk-back on scan
Some conventional radios use, or have an option for, a talk-back-on-scan function. If the user transmits when the radio is in a scan mode, it may transmit on the last channel received instead of the selected channel. This may allow users of multi-channel radios to reply to the last message without looking at the radio to see which channel it was on. Without this feature, the user would have to use the channel selector to switch to the channel where the last message occurred. (This option can cause confusion and users must be trained to understand this feature.)

This is an incomplete list of some conventional radio types:
 * Commercial and Public Safety Radio
 * Marine VHF radio
 * Family Radio Service (sometimes referred to by the abbreviation FRS)
 * UNICOM
 * Amateur radio

Trunked
In a trunked radio system, the system logic automatically picks the physical radio frequency channel. There is a protocol that defines a relationship between the radios and the radio backbone which supports them. The protocol allows channel assignments to happen automatically.

Digital trunked systems may carry simultaneous conversations on one physical channel. In the case of a digital trunked radio system, the system also manages time slots on a single physical channel. The function of carrying simultaneous conversations over a single channel is called multiplexing.

Instead of channels, radios are related by groups which may be called, groups, talk groups, or divided into a hierarchy such as fleet and subfleet, or agency-fleet-subfleet. These can be thought of as virtual channels which appear and disappear as conversations occur.

As with wide-area geographic conventional systems, geographic trunked radio systems require the user to switch channels as they travel unless the radio is equipped with automatic roaming. As of 2018, most all modern trunked radio systems were capable of automatic roaming.

Systems make arrangements for handshaking and connections between radios by one of these two methods:
 * A computer assigns channels over a dedicated control channel. The control channel sends a continual data stream. All radios in the system monitor the data stream until commanded by the computer to join a conversation on an assigned channel.
 * Electronics embedded in each radio communicate using a protocol of tones or data in order to establish a conversation, (scan-based).

If all physical channels are busy, some systems include a protocol to queue or stack pending requests until a channel becomes available.

Some trunked radios scan more than one talk group or agency-fleet-subfleet.

Visual clues a radio may be trunked include the 1) lack of a squelch knob or adjustment, 2) no monitor button or switch, and 3) a chirp (made famous by Nextel) showing the channel is available and ready at the moment the push-to-talk is pressed.

This is an incomplete list of some trunked technologies and manufacturer marketing names:
 * APCO Project 25 Phase I (trunking models)
 * APCO Project 25 Phase II
 * DMR Tier III
 * TETRA
 * Logic Trunked Radio (abbreviated LTR)
 * Motorola SmartZone and SmartNet
 * Ericsson/Harris EDACS
 * Icom IDAS Digital Advanced System
 * PositionPTT - Push to Talk Two-Way Mobile Radio communication Network

Simplex
Simplex channel systems use a single channel for transmit and receive. This is typical of aircraft VHF AM, citizen's band and marine radios. While any station is transmitting, others can only listen, since simultaneous transmission on the shared channel will garble any reception.
 * Advantage: the simplest system configuration, since only two radios are needed to establish communication between them, without any other infrastructure.
 * Disadvantages: Any station that starts transmitting while the channel is in use will obstruct communications. To prevent this, where large numbers of stations are in use, many channels will be allocated, which may be idle much of the time.

Duplex
Duplex channel systems transmit and receive on different discrete channels. All stations listen on one frequency, and transmit on a second. Because of this, a practical system requires some infrastructure such as a repeater, base station or Talk-Through Base. Most common in the US is a repeater configuration where a base station is configured to simultaneously re-transmit the audio received from mobile units. This makes the mobiles, or hand-helds, able to communicate amongst one another anywhere within reception range of the base station or repeater. Typically the base or repeater station has a high antenna and high power, which allows much greater range, compared with a ground vehicle or hand-held transceiver.

An example of duplex communication is a cellular telephone, in which both parties may speak at the same time and can hear each other continually.

This term is not used in a radio communications context.

Push-to-talk (PTT)
In two-way radios with headsets, a push-to-talk button may be included on a cord or wireless electronics box clipped to the user's clothing. In fire trucks or an ambulance a button may be present where the corded headset plugs into the radio wiring. Aircraft typically have corded headsets and a separate push-to-talk button on the control yoke or control stick. Dispatch consoles often have a hand-operated push-to-talk button along with a foot switch or pedal. If the dispatcher's hands are on a computer keyboard, the user can step on the foot pedal to transmit. Some systems have muting so the dispatcher can be on a telephone call and the caller cannot hear what is said over the radio. Their headset microphone will mute if they transmit. This relieves the dispatcher of explaining every radio message to a caller.

In some circumstances, voice-operated transmit (VOX) is used in place of a push-to-talk button. Possible uses are handicapped users who cannot push a button, amateur radio operators, firefighters, crane operators, or others performing critical tasks where hands must be free but communication is still necessary.

Analog versus digital
One example of analog radios are AM aircraft radios used to communicate with control towers and air traffic controllers. Another is a Family Radio Service walkie talkie. Analog equipment is less complex than the simplest digital.


 * Advantage: In high-quality equipment, better ability to communicate in cases where a received signal is weak or noisy.
 * Disadvantage: Only one conversation at a time can occur on each channel.

Examples of digital communication technologies are all modern cellphones plus TETRA considered to be the best standard in digital radio and being the baseline infrastructure for whole of country networks, including manufacturers such as DAMM, Rohill, Cassidian, Sepura and others, APCO Project 25, a standard for digital public safety radios, and finally other systems such as Motorola's MotoTRBO, HQT's DMR, Nextel's iDEN, Hytera's DMR, EMC's DMR, and NXDN implemented by Icom as IDAS and by Kenwood as NEXEDGE. Only NXDN and Mototrbo are proprietary. DMR is an ETSI open standard.


 * Advantage: More simultaneous talking paths are possible and information such as unit ID, status buttons, or text messages can be embedded into a single digital radio channel. The interoperability standard of TETRA means that any brand TETRA radio can work with any Brand TETRA infrastructure, not locking the user into expensive and proprietary systems.
 * Disadvantage: Radios must be designed to the same, compatible standard, radios can become obsolete quickly (although this is mitigated by properly implemented interoperability standards such as those set down by ETSI for TETRA), cost more to purchase, and are more complicated.

Data over two-way radio
In some cases, two-way radio is used to communicate analog or digital data. Systems can be simplex or duplex and may employ selective calling features such as CTCSS. In full-duplex systems, data can be sent real-time between two points. In simplex data can be sent with a time lag between many points.

Some two-way digital systems carry both audio and data over a single data stream. Systems of this type include NXDN and APCO Project 25. Other more advanced systems under the TETRA standard are capable of joining time slots together to improve data bandwidth, allowing advanced data polling and telemetry applications over radio. The method of encoding and decoding the audio stream is called a codec, such as the AMBE or the ACELP family of codecs.

After market GPS tracking and mobile messaging devices can be interfaced with popular two-way radio models providing a range of features.

Digital
Digital systems typically use data rates in the 1,200–19,200 kilobit-per-second rates and may employ modulation schemes such as frequency shift keying, audio frequency shift keying, or quadrature phase shift keying to encode characters. Modern equipment have the same capabilities to carry data as are found in Internet Protocol. Working within the system's protocol constraints, virtually anything can be sent or received.

Engineered versus not engineered
Some systems are not engineered. Legacy systems are existing systems which were never designed to meet a system performance objective. They may have started with a base station and a group of mobile radios. Over a period of years, they have equipment added on in a building block style. Legacy systems may perform adequately even though they were not professionally designed as a coherent system. A user may purchase and locate a base station with an expectation that similar systems used in the past worked acceptably. A City Road Department may have a system that works acceptably, so the Parks Department may build a new similar system and find it equally usable. General Mobile Radio Service systems are not usually engineered.

Options, duty cycle, and configuration
1940s tube-type land mobile two-way radios often had one channel and were carrier squelch. Because radios were costly and there were fewer radio users, it might be the case that no one else nearby used the same channel. A transmit and receive crystal had to be ordered for the desired channel frequency, then the radio had to be tuned or aligned to work on the channel. 12-volt mobile, tube-type radios drew several amperes on standby and tens-of-amperes on transmit. Equipment worked ideally when new. The performance of vacuum tubes gradually degraded over time. U.S. regulations required an indicator lamp showing the transmitter had power applied and was ready to transmit and a second indicator, (usually red,) that showed the transmitter was on. In radios with options, wire jumpers and discrete components were used to select options. To change a setting, the technician soldered an option jumper wire then made any corresponding adjustments.

The trend is toward increasing complexity. Modern handheld and mobile radios can have capacities as high as 255 channels. Most are synthesized: the internal electronics in modern radios operate over a range of frequencies with no tuning adjustments. High-end models may have several hundred optional settings and require a computer and software to configure. Sometimes, controls on the radio are referred to as programmable. By changing configuration settings, a system designer could choose to set up a button on the radio's control panel to function as: In most modern radios these settings are done with specialized software (provided by the manufacturer) and a connection to a laptop computer.
 * turn scan on or off,
 * alert another mobile radio, (selective calling),
 * turn on an outside speaker, or
 * select repeater locations.

Microprocessor-based radios can draw less than 0.2 amperes on standby and up to tens-of-amperes on high-powered, 100 watt transmitters.

Base stations, repeaters, and high-quality mobile radios often have specifications that include a duty cycle. A repeater should always be continuous duty. This means the radio is designed to transmit in a continuous broadcast without transmitter overheating and resulting failure. Handhelds are intermittent duty, mobile radios and base station radios are available in normal or continuous duty configurations. Continuous duty is preferred in mobile emergency equipment because any one of an entire fleet of ambulances, for example, could be pressed into service as command post at a major incident. Unfortunately budgets frequently get in the way and intermittent duty radios are purchased.

Time delay is always associated with radio systems, but it is apparent in spacecraft communications. NASA regularly communicates with exploratory spacecraft where a round-trip message time is measured in hours (like out past Jupiter). For the Apollo program and the Space Shuttle, Quindar tones were used for transmit PTT control.

Life of equipment
Though the general life term for the two-way radio is 5 to 7 years and 1 to 2 years for its accessories but still the usage, atmosphere and environment plays a major role to decide its life term (radios are often deployed in harsh environments where more fragile communication equipment such as phones and tablets may fail). There are so many speculations on the life term of two-way radios and their accessories i.e. batteries, chargers, headset etc.

Different system elements will have differing service lifetimes. These may be affected by who uses the equipment. An individual contacted at one county government agency claimed equipment used by 24-hour services wears out much faster than equipment used by those who work in positions staffed eight hours a day.

Two-way radio rental is an option for firms that need use of radios for only a limited time.

Two-way radio frequencies
Two-way radios can operate on many different frequencies, and these frequencies are assigned differently in different countries. Typically channelized operations are used, so that operators need not tune equipment to a particular frequency but instead can use one or more pre-selected frequencies, easily chosen by a dial, a pushbutton or other means. For example, in the United States, there is a block of 5 channels (pre-selected radio frequencies) are allocated to the Multiple Use Radio System. A different block of 22 channels are assigned, collectively, to the General Mobile Radio Service and Family Radio Service. The citizen's band radio service (""CB"") has 40 channels.

A channel number is just a shorthand notation for a frequency. It is, for instance, easier to remember "Channel 1" than to remember "26.965 MHz" (US CB Channel 1) or "462.5625 MHz" (FRS/GMRS channel 1), or "156.05 MHz" (Marine channel 1). It is necessary to identify which radio service is under discussion when specifying a frequency by its channel number. Organizations such as electric power utilities or police departments may have several assigned frequencies in use with arbitrarily assigned channel numbers. For example, one police department's "Channel 1" might be known to another department as "Channel 3" or may not even be available. Public service agencies have an interest in maintaining some common frequencies for inter-area or inter-service coordination in emergencies (modern term: interoperability).

Each country allocates radio frequencies to different two-way services, in accordance with international agreements. In the United States, some examples of two-way services are: citizen's band radio, Digital Electronic Message Service (DEMS), Family Radio Service (FRS), General Mobile Radio Service (GMRS), Multi-Use Radio Service (MURS), Business Radio Service (BRS), and PMR446.

Amateur radio operators nearly always use frequencies rather than channel numbers, since there is no regulatory or operating requirement for fixed channels in this context. Even amateur radio equipment will have "memory" features to allow rapidly setting the transmitter and receiver to favorite frequencies.

UHF versus VHF
UHF has a shorter wavelength which makes it easier for the signal to find its way through smaller wall openings to the inside of a building. The longer wavelength of VHF means it can transmit further under normal conditions. For most applications, lower radio frequencies are better for longer range and through vegetation. A broadcasting TV station illustrates this. A typical VHF TV station operates at about 100,000 watts and has a coverage radius range of about 60 miles. A UHF TV station with a 60-mile coverage radius requires transmitting at 3,000,000 watts. Another factor with higher frequencies (UHF) is that smaller sized objects will absorb or reflect the energy more which causes range loss and/or multipath reflections which can weaken a signal by causing an "Out of Time/Out of Phase" signal to reach the antenna of the receiver (this is what caused the "Ghost" image on old over the air television).

If an application requires working mostly outdoors, a VHF radio is probably the best choice, especially if a base station radio indoors is used and an external antenna is added. The higher the antenna is placed, the further the radio can transmit and receive.

If the radios are used mainly inside buildings, then UHF is likely the best solution since its shorter wavelength travels through small openings in the building better. There are also repeaters that can be installed that can relay any frequencies signal (VHF or UHF) to increase the communication distance.

There are more available channels with UHF. Since the range of UHF is also not as far as VHF under most conditions, there is less chance of distant radios interfering with the signal. UHF is less affected than VHF by manmade electrical noise.

Range
[Radio propagation]] conditions, which are a function of frequency are a function of] ...antenna height and characteristics, atmospheric noise, reflection and refraction within the atmosphere, transmitter power and receiver sensitivity, and required signal-to-noise ratio for the chosen modulation method. An engineered two-way radio system will calculate the coverage of any given base station with an estimate of the reliability of the communication at that range. Two-way systems operating in the VHF and UHF bands, where many land mobile systems operate, rely on line-of-sight propagation for the reliable coverage area. The "shadowing" effect of tall buildings may block reception in areas within the line-of-sight range which can be achieved in open countryside free of obstructions. The approximate line-of-sight distance to the radio horizon can be estimated from: horizon in kilometers = 3.569 times the square root of the antenna height in meters.

Other two-way radio devices
Not all two-way radios are hand-held devices. The same technology that is used in two-way radios can be placed in other radio forms. An example of this is a wireless callbox. A wireless callbox is a device that can be used for voice communication at security gates and doors. Not only can they be used to talk to people at these entry points, personnel can remotely unlock the door so the visitor can enter. There are also customer service callboxes that can be placed around a business that a customer can use to summon help from a two-way radio equipped store employee.

Another use of two-way radio technology is for a wireless PA system. A wireless PA is essentially a one-way two-way radio that enables broadcasting messages from handheld two-way radios or base station intercoms.

Recent edit conflict over introduction
There is an edit conflict over the lead paragraph. The original lead was
 * "A two-way radio is a radio transceiver that can both transmit and receive radio waves, which is used for bidirectional person-to-person voice communication with other users with similar radios, in contrast to a broadcast receiver, which only receives transmissions. Typical two-way radios work on fixed radio frequency channels, though some can scan multiple channels in order to find a valid transmission."

I changed this to
 * "A two-way radio is a radio transceiver (a radio that can both transmit and receive radio waves), which is used for bidirectional person-to-person voice communication with other users with similar radios; in contrast to a broadcast receiver, which only receives transmissions."

with the 2nd sentence moved to the article body. This has been reverted 3 times by Nightscream:      and restored by Fountains of Bryn Mawr and myself, who support the new version. --ChetvornoTALK 07:19, 22 February 2023 (UTC)

My reason for removing the 2nd sentence was that it is misleading for general readers. Two-way radios work on multiple fixed frequency channels, the top version implies that most can only use a single channel. Second, this is not present in the article body, violating MOS:INTRO. The use of multiple channels is already mentioned in the second intro paragraph; scanners here is WP:undue weight. The edit to the unsourced lead sentence fixes the erroneous implication that not all transceivers can transmit and receive - this is the definition of transceiver. --ChetvornoTALK 07:19, 22 February 2023 (UTC) --ChetvornoTALK 07:19, 22 February 2023 (UTC)
 * Early two-way radios used variable frequency tuners (essentially a tuned inductor/capacitor combination). Quartz crystal tuners were introduced and these limited the channels to the number of crystals used and provided stable frequencies that did not need much adjustment by the users. Different frequencies would be selected by switching crystals. It wasn't until the advent of more sophisticated frequency synthesiser tuners that multiple crystal based frequencies were involved and scanning frequencies was a much later innovation. The Crystal Radio Systems cite is focused on current technology and this seems to be a possible reason for the confusion. The mention of that AM cite from Encyclopedia Britannica seems to be based on a conflation of two-way radios with walkie-talkies. It is also contradicted by the history in the article. The geeksforgeeks cite looks rather spammy (a content farm kind of link). The second version is more accurate and makes more sense. Jmccormac (talk) 08:09, 22 February 2023 (UTC)


 * Chetvorno, does your insistence on inserting the word "usually" into the passage come from the source cited at the end of the passage, yes or no?


 * Does your assertion on how two-way radios work, and your claim that including the passage you moved would be "misleading" come from the cited sources, including the ones you added, yes or no?


 * Your edit left the passage "In contrast to a broadcast receiver, which only receives transmissions." without a citation. Please tell me why you did this.


 * You cited as a source Page 811 of The Modern Dictionary of Electronics, but the link you added only takes the reader to that book's cover. Scrolling down to Page 811, we see that the definition given for two-way radio consists entirely of this: "Radiotelephone communications between fixed points (base stations) and portable units." Can you please explain how this justifies removing the passage you moved to the article body, or leaving that fragment without a citation? Nightscream (talk) 15:45, 22 February 2023 (UTC)


 * Usually is a no-brainer. It is not a hill to take a stand upon. Constant314 (talk) 15:59, 22 February 2023 (UTC)


 * If that's true, then why does the cited source not indicate that?
 * Including that indicates that it is not always the case. Shouldn't this be elaborated both with an explanation, and a citation for it, per policy? Nightscream (talk) 15:44, 23 February 2023 (UTC)


 * The cited source doesn't even contain the word duplex. Constant314 (talk) 16:13, 23 February 2023 (UTC)


 * The cited source that contains it is this one, which Chetvorno removed from the lede, which is one of the reasons for this dispute.


 * Didn't you look through the edit history to familiarize yourself with what he and Fountains have been doing to the article? Nightscream (talk) 16:26, 23 February 2023 (UTC)


 * That source doesn't mention radio. Constant314 (talk) 18:55, 23 February 2023 (UTC)


 * What do you think it's referring to?


 * In any event, if you believe the word duplex should not be included in the article because the source doesn't say "radio", does that mean you believe the same thing about the word "usually", which is not in any cited source for the passage in question? Nightscream (talk) 14:54, 25 February 2023 (UTC)


 * I am just trying to guess what you see in that source that makes you want to remove the word "usually". I don't see anything that says two-way radio uses simplex in that source.  All I see in that source is the definition of simplex.  If you have a source that says duplex is never used or that simplex is always used, then it would make sense to remove the word "usually".  Until then, usually means that we don't have a source that unequivocally says that only simplex is used for two-way radio.  I am not particularly attached to the word "usually", as long as the text does not imply that simplex is always used. Constant314 (talk) 20:45, 25 February 2023 (UTC)


 * I see in the source that it does not say "usually", nor otherwise indicate this. That's why it should not be included per policy. We need sources for the inclusion of material, and not removal. We do not include material based on editor's knowledge/experience/analysis, per WP:NOR. Do you dispute this? Omitting it would simply conform to that source, without any allusion to either "usually" or "always", the latter of which was not presented nor implied by the policy-compliant version of the passage.


 * If there is a policy-based argument for that word's inclusion, or a rationale argument to ignore policy in this case, then why does Chetvorno refuse to provide it when asked for it?


 * And may I ask what is your reaction to my pointing out that the source that Chetvorno removed indeed mentions radio? You didn't respond to that above. Do you dispute this? Nightscream (talk) 16:12, 27 February 2023 (UTC)


 * The second version makes sense. The first version ignores the development of two-way radios and has some problems. The contrast of the receive-only capability of a broadcast receiver helps distinguish two-way radios from simple receivers. The first version appeared dependent on an interpretation of that Crystal Radio Systems citation which only applied to modern two-way radios and seems to be advertising copy. The "valid transmission" phrase seems to be a product of that and is misleading. There is rarely any validation of transmissions outside of digital radio. With scanning analogue two-way radios, the scan will stop on a channel if the signal strength (or even noise) on that channel is over a preset level. The phrase "valid transmission" suggested that there is some analysis of the content of the transmission. Jmccormac (talk) 00:19, 23 February 2023 (UTC)


 * Does this come from the cited source, or is it your personal knowledge? Nightscream (talk) 15:32, 23 February 2023 (UTC)


 * The "valid transmisson" phrase comes from the cited source. It goes on to mention trunked radio Trunked_radio_system and this may be the source of the confusion of analogue radio with a digital radio system and the "valid transmission" phrase. This is separate to the historical problems in the article like the addition of the AM radio citation which is contradicted by the History section. This is due to two-way radio being reduced to, or simply confused with, walkie-talkies. The cited source seems to be written as advertising copy (which in itself is problematic as an RS). On reading it, there are even some similarities with the Wikipedia article but it is also a bit more comprehensive in places. I'm not sure if some additions to the WP article are, in places, a partial synthesis of the cited source. Jmccormac (talk) 21:43, 23 February 2023 (UTC)


 * Agree with your posts that the history section is completely erroneous. Two way radio began with the development of amplitude modulation following the invention of the first continuous wave radio transmitters and rectifying detectors around 1904. I don't really mind the introduction being limited to modern crystal controlled two-way radios that use fixed channels; that's all there is now. It's just that that sentence was poorly written and unnecessary.   I'll probably rewrite the history section when I get time, if no one else has. --Chetvorno<i style="color: Purple;">TALK</i> 01:01, 23 February 2023 (UTC)


 * Can you respond to my questions above? Thanks. Nightscream (talk) 15:36, 23 February 2023 (UTC)


 * A good history section would clear up a lot of the problems with the article. Jmccormac (talk) 22:02, 23 February 2023 (UTC)


 * Following Wikipedia's policies and guidelines would clear up a lot of the problems with this article.


 * That includes conducting a discussion with straightforwardness, honesty, and transparency, which means directly responding to questions and arguments posed by others, rather than going silent, as you all have when I flat-out ask you about these matters here.


 * Saying that these problems would be solved by "a good history section" ignores this point. It also ignores the fact that the entire article is largely one of history, so saying that it needs a "section" to this effect makes little sense.


 * "The "valid transmisson" phrase comes from the cited source."
 * I'm not talking about the "valid transmission" phrase. I'm talking about the points I raised above upon which this dispute hinges. Did you not read them? Where in the sources does it say "usually", which Chetvorno inserted into a passage? What aspect of the cited source justifies Chetvorno's removing an entire passage that helps define the term to the article body, and leaving that fragment without a citation? I asked these questions above, and thus far, none of you have answered this. Can you please explain this? Thanks. Nightscream (talk) 16:12, 27 February 2023 (UTC)


 * A good history section versus a bad history section. The reference to the Galvin AM two-way radio system is ahead of the history section and is contradicted later by the history section. The history section should cover the development of two-way radio from the first 1923 reference to the present. The use of crystal tuning and then crystal based synthesisers in modern two-radios could be mentioned as part of the development and it this way the basic introduction would not have any problems. The Crystal Radio Systems document is more comprehensive than the article in places but it was used in a manner that muddled what should be a basic introduction and ignored the development of two-way radio systems. There was a discontinuity between what was supposed to be a basic introduction and the rest of the article with the citation in that place. Apart from the similarity between the article and the CRS article, there is a problem with advertising copy being used as an RS. No technology ever appears fully developed. The use of the CRS citation and mention of crystal tuning in the introduction effectively made it appear to people not clicking on the citation as if two-way radios using modern technology appeared fully developed. A simple introduction followed by a good history section on the development of two-way radio would make things far more understandable. Jmccormac (talk) 17:17, 27 February 2023 (UTC)


 * None of which addresses the policy violations prompting this discussion.


 * But if you feel there is a problem with some aspect of the article apart from those that prompted this discussion, then why not fix them? Nightscream (talk) 19:02, 27 February 2023 (UTC)

What is the difference ...?
... between a tranceiver and a two-way radio? This is not a joke! - Roxy the dog 18:15, 23 February 2023 (UTC)


 * Probably just a historical one at this stage. In the early days of radio, transmitters and receivers would have been separate pieces of equipment. A transceiver would have been an integration of the two with the transmitter and receiver in the same case as the technology evolved. Jmccormac (talk) 21:55, 23 February 2023 (UTC)