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TRANSMITTER
TEST EQUIPMENT

TM-55-1930-209-14P-12 Water Purification Barges (NSN 1930-01-234-2165) Lighting System Manual
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TM 55-1930-209-14&P-12 filter which employs aluminum slugs for insuring high Q.  It is then amplified by a J-FET common gate amplifier (QlO1) and again filtered through a high Q bandpass filter. 2. First Mixer After the initial amplification and filtering, the signal is applied to the gate of the first mixer transistor (Q102) while the first local signal is injected into the source of the mixer transistor.  This permits the mixer stage to have a wide dynamic range.  The first local frequency is obtained by the following formula. First Local Frequency = Receive Frequency - 21.40 MHz 3. First And Second IF The  heterodyning  action  of  the  first  mixer  produces  a  21.4  MHz  intermediate  frequency,  which  is  filtered  by  a crystal filter (F201), then passed to the second mixer (Q201).  The first IF signal is mixed with a 21.855 MHz signal at this stage to produce a 455 kHz intermediate frequency (second IF). The 455 kHz signal obtained at Q201 is fed through the second IF filters (F202 and F203), then amplified by limiting amplifiers Q203 and Q251. 4. Discriminator A  conventional  FM  discriminator  (L251,  L252,  Q252,  and  Q253)  is  placed  after  the  above  stages  to  recover  the audio signal from the modulated RF signal.  The audio signal is amplified by Q351 to obtain the power to drive the speaker. 5. Noise Squelch A  noise-actuated  squelch  circuit  consisting  of  a  noise  amplifier/limiter  (Q301),  noise  detector  (Q302  and  Q303), and a DC control circuit (Q304 and Q305) is included in the receiver to cut off the audio amplifier.  This eliminates static which would otherwise be heard at the speaker during intervals between received messages. MAINTENANCE GENERAL The  inherent  quality  of  the  solid-state  components  used  in  the  transceiver  will  provide  many  years  of  continuous  use without failure, assuming the unit is treated with care.  The following precautions should always be observed to pre- vent damage to the radio. 1. Never key the transmitter unless an antenna or suitable dummy load is connected to the antenna receptacle of the radio. 2. Avoid excessive supply voltage.  The voltage should not exceed 16 VDC, nor should it fall below 11 VDC. 11







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