H - Electricity – 04 – B
Patent
H - Electricity
04
B
325/53, 325/58
H04B 1/04 (2006.01) H03C 3/02 (2006.01) H04B 1/62 (2006.01)
Patent
CA 1212420
12 ABSTRACT: Generally in land mobile FM transmitters a speech signal is pre-emphasised between 300 Hz and 3 kHz where- after it is filtered to provide a sharp cut-off and in order to maintain channel integrity the maximum peak fre- quency deviation is limited. In consequence as the level of the pre-emphasised speech signal increases it is limited to a maximum peak output level which corresponds to the maximum peak frequency deviation. Heretofore the filters have had such a step response that overshoot and ringing is produced when filtering the amplitude limiter signals. As the peak of the overshoot is treated by the frequency modu- lator as the maximum peak output level then the level of undistorted speech for frequency modulation is typically 60% to 70% of the maximum peak output level. The level of undistorted speech can be raised to within 90% of the transmitter peak deviation by directly connecting the ampli- tude limiter to a filter amplifier which behaves as a level sensitive filter when the speech signal has been limited and prevents ringing and overshoot being produced. The output from the filter amplifier is coupled to a low pass filter, typically a fourth-order Butterworth filter, via an attenuator which reduces the amplitude of the signal to prevent the onset of further clipping.
423281
N.v.philips'gloeilampenfabrieken
Van Steinburg C.e.
LandOfFree
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