Antenna tower of Crystal Palace transmitter, London
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Transmitters

A transmitter (sometimes abbreviated XMTR) is an electronic device which with the aid of an antenna propagates an electromagnetic signal such as radio, television, or other telecommunications. more...

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A transmitter usually has a power supply, an oscillator, a modulator, and amplifiers for audio (AF), intermediate frequency (IF) and radio frequency (RF). The modulator is the device which piggybacks (or modulates) the signal information onto the carrier frequency, which is then broadcast. Sometimes a device (for example, a cell phone) contains both a transmitter and a radio receiver, with the combined unit referred to as a transceiver.

More generally and in communications and information processing, a "transmitter" is any object (source) which sends information to an observer (receiver). When used in this more general sense, vocal cords may also be considered an example of a "transmitter".

In industrial process control a "transmitter" is any device which converts measurements from a sensor into a signal to be received, usually sent via wires, by some display or control device located a distance away. Typically in process control applications the "transmitter" will output a 4-20 mA current loop or digital protocol to represent a measured variable within a range. For example, a pressure transmitter might use 4 ma as a representation for 50 psig of pressure and 20 ma as 1000 psig of pressure and any value in between proportionately ranged between 50 and 1000 psig. Older technology transmitters used pneumatic pressure typically ranged between 3 to 15 psig (20 to 100 kPa) to represent a process variable.

History

In the early days of radio engineering, radio frequency energy was generated using arcs or mechanical alternators (of which a rare example survives at the SAQ transmitter in Grimeton, Sweden). In the 1920s electronic transmitters, based on vacuum tubes, began to be used.

Electromagnetic concepts

In principle any conductor (wire) carrying an alternating current will radiate a radio signal. Thus a basic transmitter is just an oscillator connected directly to a wire antenna.

Since transmitters require excellent frequency stability, there are usually several amplifier stages between oscillator and antenna. The intermediate amplifier stages prevent changes in the antenna circuit from affecting the frequency of the oscillator. Often the transmitter frequency is not the frequency produced by the oscillator, but one of its harmonics. This is generated from the oscillator's output by a non-linear device (e.g. a diode or an overdriven amplifier), then filtered with combinations of inductors and capacitors, and then amplified.

Special standard frequency transmitters use frequency synthesis referenced to a very stable atomic clock. Since this procedure, which gives the most precise carrier frequencies, is very complex, it is not used in most transmitters. Typically a quartz crystal is used as a frequency reference, which provides adequate stability for nearly all purposes. Historically mechanically tuned variable-frequency oscillators were used, and are still found in classic amateur radio and antique equipment.

Read more at Wikipedia.org


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Little Joe "Universal" 10 Meter Qrp Transmitter, Beacon $15.00 B & W Antenna Switch Model 380 $24.95
Antenna Relays / High Voltage Relays $19.95 Uhf Cavity Filters Phelps Dodge 406 - 512 Mhz $24.95
Bird Meter 43 element (Slug) 50 watt , 25-60 Mhz $9.95 Socket for Soviet Tube Gu-74B Tetrode 4Cx800A Ham Radio $19.99
Tube Gu-43B 1,6 Kw Frq. 100Mhz Tetrodes Ham Radio $49.99 Johnson Pacemaker Hf Transmitter, **Vintage**, Gc, Nr $99.99
Vr100 - R1155 Receiver $9.77 Socket For Russian Tubes Gs31B / Gs 31B Gs35B / Gs 35B $159.00
Globe Electronics Dsb 100 Sidebander Dsb/Am/Cw Xmtr $22.50 Globe King 500B Am Transmitter W/Eico 730 Modulator $1,000.00
5 Watt Fm Radio Transmitter- New Wonderful Golden Shell $9.98 6W Fm Radio Station Transmitter Board--Pll Stereo $9.98
"Vintage"Heathk it Dx60B Transmitter And a Hg-10 Vfo!!! $24.99 Ef Johnson Whip Antenna Tuning Unit $24.95
High Voltage Transformer $19.95 Ham radio speaker Kenwood S-599 twins $26.00
Ham radio receiver Kenwood R-599 twins $10.00 Ham radio transmitter Kenwood T-599D twins $21.00
Rci 2950Dx 10 & 12 Mtr Radio "Like New" $102.50 4 Ohm Signal Telegraph Key & Sounder Set-Vintage-Works $15.50
Johnson 6N2 Two Meter Transmitter $15.00 Socket for Soviet Tube Gu84B / Gu 84B with Chimney Used $159.00
E.F. Johnson Model 250-20 Low Pass Filter for Ham/Cb $9.99 Vertex Standard Vxa-300 Nav/Com Aviation Transciever $224.69
Swan 350 and Swan 508 both with Power Supply, Hf radio $315.00 Mixed Lot Of Cr-18/U - 23/U -27/U Transmitter Crystals $9.99
Yaesu Vx-6E Two way Handheld radio Vx6R Vx-6R Vertex $234.44 General Electric Ge High Voltage Capacitor Cb Ham Radio $1.95
Sma to Bnc adaptor Yaesu Vx-177 Vx-1R Vx-2R Vx-6R Vx-7R $6.84 Icom - Yaesu - Kenwood/Trio - Alinco Manuals on 2 Dvd's $1.99
Icom Ct17 Ci-V / Cat Interface / level convertor $16.99 Vacuum Variable Capacitor 20-1000 pF 10kV 50A, Used $129.00
Vacuum Variable Capacitor 20-1000 pF 10 kV 50 A 30 Mhz $159.00 Russian Nos tube Gu43B 1600W, 100Mhz $69.00
Socket for Russian (Soviet) Tube Gu 73B / Gu73B $35.00 Silver plated soft copper wire 1mm x 2M $1.93
Repco 2Watt Vhf Transmitter Board Possible Military New $9.95 50'S~Swr Meter~ Transmitter~Dc Microamperes Triplett $2.99
(10) New Rf Chokes f/ Ham Radio Transmitter / Receiver $5.99 Ten Tec Model 960 Power Supply -- Very Nice! $25.00
Ef Johnson 250-37 Swr Meter and Probe 1 Kw rating $24.99 Wwii Military radio aircraft transmitter Ham? Bc-457-A $9.99
Old Wwii Military radio transmitter Ham? T-282D/Gr $99.99 Old Gonset Gsb-100 Ssb Ham Radio transmitter model 3233 $40.00
Old B&W 51Sb Single Sideband Generator ham radio thing $21.00 Old B&W 5100-B Ham radio Transmitter Am? Fm? $10.49
Homebrew Cw Xmtr $34.00 Dentron Jr. Monitor Like New $25.00
Stancor Hamanuals - Ham Transmitter Projects 1939 1940 $1.95 Mpx170S- 45dB Seperation Stereo Encoder $30.00
Tx175-450mW Stereo Fm broadcast transmitter Great Gift! $199.00 nautel broadcast fm transmitter $1,500.00
Interface cable for Yaesu Radio Vx-2R Vx-5R Vx-6R Vx-7R $18.56 Drake T4Xc Transmitter - Tech Special! Needs Work! $56.00
Complete 300W Lpfm Stereo Broadcast Radio Station $760.00 Heathkit Sb-221 2Kw Linear Amplifier Works $255.00
5W Fm broadcast transmitter $10.50 Collins 32S-1 Transmitter $304.99
Qrp Transmitter $5.95 Collins Ham Radio S-Line slug rack $9.95
25 Watt Pll Stereo Fm Broadcast Radio Transmitter $450.00 Vacuum Variable Capacitor 5-250/5kV-75A New and Sealed $59.95
Heathkit Sb-634 Station Console great condition $57.09 Lot Of 25 Wwii Cr-23/U 50.50000 Mc Crystals N.O.S. $4.99
Near Mint & Rare Ameco Tx 62 2M & 6M Transmitter Nr $15.50 Bud Isotex Coil Form $15.00
Car Fm Radio Boardcast Wireless Transmitter Mp3 Music $8.77 Lot of 6 Crystals Ham Radio Texas Crystals, Tru Lite $9.99
Electro-Voice 719 Ceramic Microphone Made in Usa $15.00 Bendix King Kx99 Handheld Vhf Aircraft Transceiver $20.00
Glenayre Two Way Paging System 940.3250 $475.00 E.F. Johnson Air Variable Capacitor 67 - 7uf 2000V Nib $7.99
High Power Choke Transformer Transmitter Cb Ham Radio $1.95 Large 560 pF/Section Variable Capacitor Ham Amplifier $15.00
Utc Model Cvm-0 Varimatch Modulation Transformer $72.00 New Unused High Voltage Supply Transformer & Chokes $72.00
Heathkit Cheyenne Hf Transmitter Mt-1 For Parts Repair $9.95 Vintage E.F. Johnson Viking 6N2 Transmitter $15.00
Vintage Bc 625 2 Meter Transmitter Bc-625 2-Meter 5017 $5.00 Heathkit Dx-20 Crystal Controlled Cw Transmitter $31.00
Russian Soviet Tube Gu-74B Tetrode 4Cx800A Ham used $19.99 Arc-5 Series Radios Rack Shock Mounts (4) $42.96
Arc-5 T-23 Vhf Transmitter Chassis Easy Repair $29.31 Vacuum Relay W2W. 5.0 kW Spst Relay New In Box! $24.95
High Power Ferrite Choke Transmitter Cb Ham Radio $1.95 U.S. Navy Flameproof Telegraph Key Morse Code Ham Radio $65.00
500+ Ham Radio Manuals on dvd in pdf swan drake hallic $9.95 Kenwood T599 to restore parts unit $2.25
Gu-84B/4Cx2500A Svetlana Tube. Nos. $139.50 Drake Tr-3 Transceiver $50.00
Yaesu Vx-6R Two way Handheld radio Vx6R Vertex $234.44 250W Stereo Fm Broadcast Radio Transmitter Var. output $1,550.00
25W Fm Broadcast Amplifier 1W input 87-108Mhz No-tune! $125.00 Wouxun Kg-669 Uhf400-470 Fm Radio Built In Kg669 Mint $47.87
Yaesu Vx-7R Triple band Handheld radio/scanner Vx7R $350.30 5W Fm Radio Station Broadcast Transmitter-Silver Color $58.61
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Prices current as of last update, 12/19/06 1:39am.