MIL-STD-188-243 Tactical Single Channel Ultra High Frequency UHF Radio CommunicationsThe purpose of this document is to establish the minimum essential interoperability and performance requirements necessary for tactical single channel UHF radio communications equipment. This standard addresses ground-to-air, air-to-air, ship-to-shore and ship-to-ship tactical single channel UHF radio communications equipment. The requirements established by this document may be exceeded in order to satisfy specific operational requirements or to incorporate technological improvements, provided that interoperability be maintained.

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MIL-STD-188-243A

5.2.2.3 Transmitter Interfaces.

5.2.2.3.1  Local  Audio  Input  Impedance.  All  transmit  radio  equipment  shall  have  one  local microphone or handset input with an impedance of 150 ohms unbalanced. This input shall have a minimum return loss of 26 dll against a 150-ohm resistance over the frequency range from 300

Hz to 3500 Hz. Additional balanced or unbalanced local audio inputs and strap options shall be optional.

5.2.2.3.2   Local   Audio   Input   Signal   Level.   The   transmit   radio   equipment   shall   process microphone/handset inputs between -35 dBm and +10 dBm.

5.2.2.3.3  Line  Audio  Input  Impedance.  Transmit  radio  equipment  requiring  a  line  audio  input shall have at least one line input with an impedance of 600 ohms balanced, with a' minimum return loss of 26 dB against a 600-ohm resistance over the frequency bandwidth from 300 Hz to

3500 Hz. The electrical symmetry should be sufficient to suppress longitudinal currents to a level which is at least 40 dB below reference level (-40 dBm0).   Additional balanced or unbalanced local audio inputs and strap options shall be optional.

5.2.2.3.4 Line Audio Input Signal Level. The transmit radio equipment with line inputs installed shall process line audio input signals bet we en -15 d13m and +1O dB m. The nominal audio input level shall be 0 dBm.

5.2.2.3.5   RF   Output   Impedance.   The   nominal   RF   output   impedance   shall   be   50   ohms, unbalanced to  ground. The transmitter shall deliver full rated output power over the operating range  to  a  nominal  50-ohm  unbalanced  line  with  a  maximum  voltage  standing  wave  ratio (VSWR) of 2.0:1 (DO 3.0:1). The transmitter shall not be damaged by operation into a load with a VSWR greater than 3.0:1, including circuit.

5.2.2.4 Transmitter Noise and Distortion.

5.2.2.4.1 Carrier Noise Level. The AM carrier noise level shall be at least 50 dB (DO 60 dB) below the unmodulated carrier level at full rated RF output power, The FM carrier noise level shall  be  at  least  40  dB  (DO  50  dB)  below  the  carrier  level  at  full  rated  RF  output  power. Measurements shall be taken with the  audio input terminated into its characteristic impedance with no audio drive applied. The measuring device shall have the same bandwidth as the radio equipment, reference paragraph 5.2.1.7.

5.2.2.4.2 Harmonic Distortion. Any in-band harmonic distortion product produced by any single test signal within the operating audio input frequency range sha13 be a maximum of -33 dBm0 (DO -43 dBm0) at full rated RF output power.   In the AM mode measurements shall be taken with  the  audio  input  signal  adjusted  to  produce  90  percent  modulation.    Narrowband  FM measurements shall be made with the audio input signal adjusted to produce a peak deviation of

5  kHz.  Wideband  FM  measurements  shall  be  made  with  the  audio  input  signal  adjusted  to produce a peak deviation of 20 kHz.

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