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f versus vhf 5 range 6 see also 7 references 8 external links toggle the table of contents two way radio 20 languages العربية català dansk deutsch eesti فارسی suomi עברית íslenska 日本語 bahasa melayu norsk nynorsk norsk bokmål polski svenska ไทย türkçe українська اردو tiếng việt edit links article talk english read edit view history tools tools move to sidebar hide actions read edit view history general what links here related changes upload file permanent link page information cite this page get shortened url switch to legacy parser print export download as pdf printable version in other projects wikimedia commons wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia communication device this article is about two way radio in general for hand held two way radios see walkie talkie this article needs more citations please help improve this article by adding citations to reliable sources unsourced material may be challenged and removed find sources two way radio news newspapers books scholar jstor july 2022 learn how and when to remove this message naval air traffic controller communicates with aircraft over a two way radio headset a variety of portable handheld two way radios for private use 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 1 in contrast to a broadcast receiver which only receives transmissions two way radios usually use a half duplex communication channel which permits two way communication albeit with the limitation that only one user can transmit at a time this is in contrast to simplex communication in which transmission can only be sent in one direction and full duplex which allows transmission in both directions simultaneously this requires users in a group to take turns talking the radio is normally in receive mode so the user can hear all other transmissions on the channel when the user wants to talk they press a push to talk button which turns off the receiver and turns on the transmitter when the button is released the receiver is activated again multiple channels may be provided so separate user groups can communicate in the same area without interfering with each other and some radios are designed to scan the channels in order to find a valid transmission other two way radio systems operate in full duplex mode in which both parties can talk simultaneously this requires either two separate radio channels or channel sharing methods such as time division duplex tdd to carry the two directions of the conversation simultaneously on a single radio frequency 2 the first two way radio was an am only device introduced by the galvin manufacturing corporation now known as motorola solutions in 1940 for use by the police and military during world war ii and followed by the company s 1943 introduction of the walkie talkie 3 the best known example of a two way radio 4 history edit vhf marine radio on a ship two way radio in a fire truck used by firefighters to communicate with their dispatcher the first truly mobile two way radio equipment was developed in australia in 1923 by senior constable frederick william downie of the victorian police the victoria police were the first in the world to use wireless communication in cars putting an end to the inefficient status reports via public telephone boxes which had been used until that time the first sets occupied about half of the floor in the back seat of the lancia patrol cars 5 in 1933 the bayonne new jersey police department successfully operated a two way system between a central fixed station and radio transceivers installed in police cars this allowed rapidly directing police response in emergencies 6 types edit several portable two way radios designed for public services police fire rescue compatible with the project 25 digital radio standard a mobile citizen s band radio in a truck two way radio systems can be classified in several ways depending on their attributes conventional versus trunked edit conventional edit in multi channel systems channels are used for separate purposes 7 scanning in conventional radios edit scan features are either not used or scan lists are intentionally kept short in emergency applications part of apco project 16 set standards for channel access times and delays caused by system overhead scan features can further increase these delays one study said delays of longer than 0 4 seconds 400 milliseconds in emergency services are not recommended 8 duplex edit the term half duplex is applied to wired communication systems where the circuit can send information in one direction at a time but not both directions at the same time 9 advantage duplex channels usually allow repeater operation which extends range in most cases due to increased transmit power and improved aerial location height especially where hand held radios are in use disadvantage if a radio cannot reach the repeater it cannot communicate this can be mitigated with a talk around or car to car setting where stations out of range of the base can speak directly to each other alternating transmitting and receiving roles in simplex fashion on a single frequency 10 analog edit analog systems may communicate a single condition such as water level in a livestock tank a transmitter at the tank site continually sends a signal with a constant audio tone the tone would change in pitch to indicate the tank s water level a meter at the remote end would vary corresponding to the tone pitch to indicate the amount of water present in the livestock tank similar methods can be used to telemeter any analog condition this type of radio system serves a purpose equivalent to a 4 20 ma current loop 11 in the us mid band 72 76 mhz or uhf 450 470 mhz interstitial channels are often used for these systems some systems multiplex telemetry of several analog conditions by limiting each to a separate range of tone pitches for example 12 analog systems may also transmit voice in the same frequency bands except for vhf mid band but with the addition of vhf low band 25 50 mhz historically all two way voice communications was analog digital edit digital systems may communicate text messages from computer aided dispatch cad for example a display in a tow truck may give a textual location for a call and any related details the tow truck driver may press an acknowledge button sending data in the opposite direction and flagging the call as received by the driver they can be used for analog telemetry systems such as the livestock tank levels as described above another possibility is the lubricating oil pressure in a transit bus engine or the current speed of the bus analog conditions are translated into data words some systems send radio paging messages which can either 1 beep a paging receiver 2 send a numeric message or 3 send a text message 13 engineered systems edit engineered systems are designed to perform close to a specification or standard citation needed they are designed as systems with all equipment matched to perform together for example a modern local government two way radio system in the us may be designed to provide 95 area coverage in an urban area system designers use radio frequency models terrain models and signal propagation modeling software in an attempt to accurately estimate where radios will work within a defined geographic area the models help designers choose equipment equipment locations antennas and estimate how well signals will penetrate buildings these models will be backed up by drive testing and actual field measurements of parameters such as received signal strength bit error rate or delivered audio quality designers adjust antenna patterns add or move equipment sites and design antenna networks in a way that will accomplish the intended level of performance 14 options duty cycle and configuration edit example of control arrangement on a configured p25 capable hand held radio many mobile handhelds have a limited duty cycle duty cycle is the ratio of listening time to transmit time and is generally dependent on how well the transmitter can shed the heat from the heat sink on the rear of the radio a 10 duty cycle common on handhelds translates to 10 seconds of transmit time to 90 seconds of receive time some mobile and base equipment is specified at different power levels for example 100 duty cycle at 25 watts and 15 at 40 watts 15 motorola mototrbo repeater dr3000 with duplexer mounted in a flight case 100 duty cycle up to 40 w output life of equipment edit in government systems equipment may be replaced based on budgeting rather than any plan or expected service life funding in government agencies may be cyclical or sporadic managers may replace computing systems vehicles or budget computer and vehicle support costs while ignoring two way radio equipment equipment may remain in use even though maintenance costs are unreasonable when viewed from an efficiency standpoint 16 one document says seven years is beyond the expected lifetime of walkie talkies in police service batteries are cited as needing replacement more often twelve year old dispatch consoles mentioned in the same document were identified as usable these were compared to problematic 21 year old consoles used elsewhere in the same system 17 another source says system backbone equipment like consoles and base stations are expected to have a fifteen year life mobile radios are expected to last ten years walkie talkies typically last eight 18 in a state of california document the department of general services reports expected service life for a communications console used in the department of forestry and fire protection is 10 years 19 two way radio frequencies edit the examples and perspectives in this section deal primarily with the united states and do not represent a worldwide view of the subject you may improve this section discuss the issue on the talk page or create a new section as appropriate october 2012 learn how and when to remove this message two gmrs radios a hand mic and two frs radios typical two way radios work on fixed radio frequency channels though some can scan multiple channels in order to find a valid transmission 4 unreliable source in an analog conventional system the simplest type of system a frequency or channel serves as a physical medium or link carrying communicated information the performance of a radio system is partly dependent on the characteristics of frequency band used the selection of a frequency for a two way radio system is affected in part by 20 government licensing and regulations local congestion or availability of frequencies ground cover since radio signals travel differently in forests and urban viewsheds terrain which may cause shadowing of radio paths the presence of noise interference or intermodulation 20 uhf versus vhf edit the most common two way radio systems operate in the vhf and uhf parts of the radio spectrum because this part of the spectrum is heavily used for broadcasting and multiple competing uses spectrum management has become an important activity of governments to regulate radio users in the interests of both efficient and non interfering use of radio both bands are widely applied for different users 21 range edit the useful direct range of a two way radio system depends on radio propagation conditions which are a function of frequency 22 there are other factors that affect the range of a two way radio such as weather exact frequency used and obstructions 22 23 see also edit tetra terrestrial trunked radio astro motorola digital mobile radio paraset personal radio service ge marc v project 25 quik call i motorola saber mobile radio professional mobile radio specialized mobile radio mobile radio telephone police radio radiotelephony references edit graf rudolf f 1999 modern dictionary of electronics 7th ed elsevier p 811 isbn 9780080511986 goldsmith andrea 8 aug 2005 wireless communications cambridge university press isbn 9780521837163 retrieved 20 april 2016 hall mark october 3 2022 motorola inc encyclopædia britannica archived from the original on january 18 2023 retrieved january 17 2022 1 2 a complete guide to two way radios crystal radio systems ltd archived from the original on june 26 2022 retrieved january 17 2023 haldane robert 1995 the people s force a history of the victoria police melbourne university press isbn 0 522 84674 2 1995 ieee history milestones retrieved oct 2 2007 one example of purpose specific channel assignments is described in ivanov d a v p savelyev and p v shemanski organization of communications fundamentals of tactical command and control a soviet view soviet military thought series 18 washington d c superintendent of documents 1977 library of congress control number 84602565 this is a us air force translation of a soviet era russian language book see also inadequate system capacity special report improving firefighter communications usfa tr 099 january 1999 emmitsburg maryland u s fire administration 1999 pp 18 19 and 5 2 present system the california highway patrol communications technology research project on 800 mhz 80 c477 sacramento california department of general services communications technology division 1982 pp v 4 v 6 3 4 1 user equipment general deficiencies san rafael police radio committee report to mayor and city council san rafael california city of san rafael 1995 pp 12 ieee 100 the authoritative dictionary of ieee standards terms seventh edition ieee press 2000 isbn sbn 0 7381 2601 2 for an example of talk around use see problem reporting special report improving firefighter communications usfa tr 099 january 1999 emmitsburg maryland u s fire administration 1999 pp 25 26 this article also confirms the definition of the phrase talk around for examples see mikhailov k e 1965 communications facilities on the volga moscow transmission line long distance electrical transmission between the v i lenin hydroelectric station and moscow jerusalem israeli program for scientific translations for an electrocardiogram telemetry example see planning emergency medical communications vol 2 local regional level planning guide washington d c national highway traffic safety administration us department of transportation 1995 p 48 spartan training bulletin volume one issue one retrieved october 18 2017 for two examples of drive testing and field measurements of parameters such as received signal level bit error rate or delivered audio quality see section ii radio propagation studies the california highway patrol communications technology research project on 800 mhz 80 c477 sacramento california department of general services communications technology division 1982 pp ii 1 ii 34 ossanna joseph f jr a model for mobile radio fading due to building reflections theoretical and experimental fading waveform power spectra bell system technical...