= changeant constamment de fréquence, par ex.

"GLOTEL - RFC - Free
http://abcdrfc.free.fr/ressources-vf/GLOTEL.rtf
A2O (Ordinary quality voice bandwith 2-wire analogue leased line) = liaison ..... allocated radio services = services hertziens bénéficiant d'attributions de fréquences ...... keyed carrier = porteuse verrouillée ; porteuse manipulée (Termite)."

http://www.granddictionnaire.com/ficheOqlf.aspx?Id_Fiche=189...
http://www.granddictionnaire.com/ficheOqlf.aspx?Id_Fiche=104...

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Note added at 10 hrs (2014-09-14 07:10:51 GMT)
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"Continuously Keyed versus Switched Carrier Operation
The keying behavior of the master station can be used to describe an MAS system.
Continuously Keyed operation means the master station transmitter is always
keyed and an RF carrier is always present, even when there is no data to send.
The master station is always simultaneously transmitting and continuously listening.
Different frequencies must be used for transmit and receive. This is the
method used in many MAS systems, and is shown in Figure 2. This is useful
for high-speed polling applications."
3634A 4710 Body.book - GE Digital Energy
https://www.gedigitalenergy.com/products/.../3634B_4710_RevB...

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Note added at 23 hrs (2014-09-14 20:28:26 GMT)
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"MODULATION TECHNIQUE USED IN GSM IS GMSK

Gaussian Minimum Shift Keying (GMSK) is a form of modulation used in a variety of digital radio communications systems. It has advantages of being able to carry digital modulation while still using the spectrum efficiently. One of the problems with other forms of phase shift keying is that the sidebands extend outwards from the main carrier and these can cause interference to other radio communications systems using nearby channels.

In view of the efficient use of the spectrum in this way, GMSK modulation has been used in a number of radio communications applications. Possibly the most widely used is the GSM cellular technology which is used worldwide and has well over 3 billion subscribers."
http://www.ukessays.com/essays/information-technology/gaussi...

contrôleur radio pour système HVAC : doit être protégé contre les interférences des "keyed radios", ou "phase-shift keyed radios":

"2. Controller in the system shall continually check its processor and memory circuit status and shall generate an alarm on abnormal operation. System shall continuously check controller network and generate alarm for each controller that fails to respond.
i. Immunity to Power and Noise. Controllers shall be able to operate at 90% to 110% of nominal voltage rating and shall perform an orderly shutdown below 80% nominal voltage. Operation shall be protected against electrical noise of 5 to 120 Hz and from keyed radios up to 5 W at 1 m (3 ft)."

"Mobile Communications Chapter 2: Wireless Transmission
http://www.mi.fu-berlin.de/inf/groups/.../C02-Wireless_Trans...
SHF and higher for directed radio links, satellite communication ..... good protection against interference ... Modulation of digital signals known as Shift Keying."