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Direct Digital Synthesis of Precision Test Signals
Delta Electronics, Inc. is a licensed manufacturer of C-QUAM® Exciters and Monitors for compatible AM Stereo transmission by AM broadcast stations. Delta engineers found that no primary reference generator of satisfactory accuracy was available for the development, calibration and testing of this equipment. The CQS series of synthesizers uses direct digital synthesis to produce the precision test signals required. The Model CQS-4 incorporates a high output amplifier and 63 dB programmable attenuator to increase the capabilities over earlier versions. The CQS-4 and earlier models are currently used in testing stereo decoder integrated circuits, calibrating modulation monitors, production testing of C-QUAM receivers and as a primary reference for the manufacture of C-QUAM stereo exciters. The synthesizer is manufactured under U.S. Patent Number 4,758,971.
Typical Performance Characteristics
Pattern Accuracy:
The synthesizer is intended as a primary reference for testing C-QUAM circuitry and components. To our knowledge, there is no equipment capable of resolving the accuracy of the patterns. Particular attention to the design of the synthesizer circuitry has minimized known sources of error: quantizing error, D/A settling time error, strobe phase jitter, etc. The following data are believed to reasonably represent the pattern accuracy for modulation frequencies of 500, 1000, and 2000 Hz.
L+R High Order Sidebands: -65 dB
L, R THD: .2% or less
L+R THD: .1% or less
L/R, R/L Separation: 50 dB
L+R IPM: -50 dB
Pattern Stability:
As opposed to an analog circuitry, the digital synthesis approach used in the synthesizer has very high long term stability and repeatability. There are no critical circuit adjustments to vary.
Technical Specifications:
Front Panel Components
BNC Output Connector:
RF output, 50 Ohm source, 500 mVrms Max. (carrier level) into 50 Ohms; adjustable in 1 dB steps.
Output Attenuator:
Adjustable in 1 dB steps from 0 dB to 63 dB attenuation.
BNC SYNC Connector:
TTL level sync. Negative transition synchronous with start of pattern.
f0, +-f1, --f1, +-f2, --f2
Select Switch:
Selects carrier frequency:
f0 = 450 kHz +5 Hz
+-f1 = f0 + 250 Hz
--f1 = f0 - 250 Hz
Optional +-f2 = f0 + 2 kHz
Optional --f2 = f0 - 2 kHz
(Other -f values available on special order)
Pattern Select Switch: Selects one of 15 modulation patterns. Standard patterns (Pattern Bank 1):
(1) L+R 25% (9) L-R 100%
(2) L+R 50% (10) L 25%
(3) L+R 75% (11) L 50%
(4) L+R 100% (12) L 75%
(5) L+R 95% (13) R 25%
(6) L+R +125%, -100% (14) R 50%
(7) L-R 50% (15) R 75%
(8) L-R 90% (16) 7 TONES
(Customer specified patterns on special order)
Pattern Bank Switch:
Enables optional second memory board with 16 additional modulation patterns.
Modulation Frequency Switch:
Selects modulation frequencies of 62.5, 125, 250, 500 Hz, 1, 2, 4, 8 kHz. (C-QUAM spectra most accurate .5-2 kHz.)
Pilot Select Switch:
This four position rotary switch selects no pilot (O position) or a 25 Hz pilot tone with one of the following levels:
4% pilot(x ±2.29º), 5% pilot (x ±2.86º), or 6% pilot (x ±3.43º)
Pulse/Carrier Switch:
This is a three position toggle switch. Switch "down" selects the unmodulated carrier. Switch at "center" selects the modulation pattern in accordance with the Pattern Select Switch setting. Switch "up" selects pulse pattern at 64 cycles of selected modulation and approximately one second unmodulated carrier.
Co-Channel Switch:
This is a two position toggle switch. Switch "up" phase modulates ±5º at 6 Hz the carrier or the pattern established by the Pattern Select Switch setting. Switch "down" turns off the phase modulation.
Power Switch:
This alternate action pushbutton switch controls the application of AC power. When AC power is applied, the switch is illuminated.
Rear Panel Components
AC Cord Connector:
120/240 VAC, 50/60 Hz.
Local/Remote Jumper:
When jumper is in place, front panel controls function as described. When jumper is removed, front panel controls are not functional and remote connector is enabled.
Remote Connector:
37 pin "D" connector (mating connector supplied) for TTL compatible, transistor pulldown, or dry contact remote control of all functions described above except AC power.
Note: Specifications are subject to change without notice
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