Note
QST, Dec 1966, p. 161.
QST, Jun 1973, p. 167.
The Comdel CSP-11 is an all-solid-state, distortion-free speech processor designed to increase the average "talk power" (by over 10 dB) of voice communications systems—particularly Single Sideband (SSB) radio transmitters and public address setups—without introducing the heavy harmonic distortion typical of standard audio clippers.
Standard audio clippers create square waves that produce harsh odd harmonics. When fed into an SSB transmitter, the phase relationships break down, recreating high peak amplitudes and defeating the clipper's purpose. By converting audio to a higher IF frequency before limiting and using a bandpass filter to eliminate the harmonic components prior to audio demodulation, the CSP-11 yields a peak-limited audio waveform free of harmonic distortion.
– Balanced Mixer & Local Oscillator: Translates speech to high-frequency IF.
– Limiting IF Amplifier & Filter: Limits peaks and filters out spurious harmonics.
– Product Detector / Mixer & Low-Pass Filter: Demodulates the signal back down to clean, processed baseband audio.
Specifications
– Processing Architecture: RF envelope limiting / SSB processing. The incoming audio signal (centered around 1.5 kHz) is up-converted to a higher IF, peak-limited, filtered to remove out-of-band harmonics, and then demodulated back to audio.
– Talk Power Gain: 10 dB.
– Frequency Response: Tailored for voice intelligibility, rated at -3 dB at 500 Hz and 2500 Hz.
– Input / Output Levels:
Input level at limiting point: 10 mV peak.
Output level at limiting point: 40 mv peak.
– Designed for high-impedance (0.5 M ohms) microphones with voice peaks of at least 25–35 mV.
Power Requirements: 9 VDC at 18 mA.
Can be powered internally using six 1.5V "D" cells (giving 300 to 500 hours of battery life, or double with PTT wiring).
Can run externally off 9 VDC, 12 VDC automotive power, or higher DC voltages using a series dropping resistor.
References
Review. 73, Nov 1967, p. 94.
