The magnetron and other microwave components of an early <a href="https://en.wikipedia.org/wiki/X_band" class="extiw" title="w:X band">X band</a> commercial airport <a href="https://en.wikipedia.org/wiki/radar" class="extiw" title="w:radar">radar</a> transmitter, the De Mornay-Budd No. 412 RF unit, from an advert in a 1947 electronics magazine.  It consists of a 9.375 GHz 20 kW peak power <a href="https://en.wikipedia.org/wiki/cavity_magnetron" class="extiw" title="w:cavity magnetron">cavity magnetron</a> tube <i>(right)</i> mounted between the poles of two <a href="https://en.wikipedia.org/wiki/alnico" class="extiw" title="w:alnico">alnico</a> horseshoe magnets, its output feeding into a <a href="https://en.wikipedia.org/wiki/waveguide" class="extiw" title="w:waveguide">waveguide</a> with a TR (transmit/receive) switch, connected to the receiver portion of the radar <i>(upper waveguide)</i>.  The waveguide aperture <i>(left)</i> is connected to the waveguide going to the dish antenna <a href="https://en.wikipedia.org/wiki/feed_horn" class="extiw" title="w:feed horn">feed horn</a>.<br><br>
In operation, the magnetron emits brief pulses of microwaves.  During each pulse the 1B35 ATR and 1B24 TR tubes making up the TR switch is set to "transmit" to protect the sensitive receiver from the powerful output.   Each pulse passes through the TR switch and waveguide to the antenna.  Then the TR switch is set to "receive".  The weak return pulse of microwaves reflected by the aircraft is received by the antenna and passes back down the waveguide to the TR switch, which routes it to the <a href="https://en.wikipedia.org/wiki/superheterodyne" class="extiw" title="w:superheterodyne">superheterodyne</a> receiving components in the upper waveguide section.  Here a 2K25 <a href="https://en.wikipedia.org/wiki/reflex_klystron" class="extiw" title="w:reflex klystron">reflex klystron</a> tube generates a <a href="https://en.wikipedia.org/wiki/local_oscillator" class="extiw" title="w:local oscillator">W:local oscillator</a> signal.  This is mixed with the return signal in a 1N21 point-contact <a href="https://en.wikipedia.org/wiki/germanium_diode" class="extiw" title="w:germanium diode">germanium diode</a> mixer.  The <a href="https://en.wikipedia.org/wiki/intermediate_frequency" class="extiw" title="w:intermediate frequency">intermediate frequency</a> (IF) is filtered from the output of the diode by a vacuum tube IF amplifier section and creates the display on the radar screen <i>(not shown)</i>.  The capped coaxial connecter <i>(lower left)</i> is a <a href="https://en.wikipedia.org/wiki/directional_coupler" class="extiw" title="w:directional coupler">directional coupler</a> which allows the output to be conveniently sampled.
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Retrieved June 18, 2014 from <a rel="nofollow" class="external text" href="http://www.americanradiohistory.com/Archive-Tele-Tech/Tele-Tech-1947-01.pdf"><i>Tele-Tech</i> magazine, Caldwell-Clements Inc., New York, Vol. 6, No. 1, January 1947, p. 99</a> on <a rel="nofollow" class="external free" href="http://www.americanradiohistory.com">http://www.americanradiohistory.com</a>