Summary
Summary
The Model SD-31 Synthesizer-Detector is a high output crystal signal generator of precisely known frequency combined with a sensitive, selective detctor for RF bridge measurements of AM antenna impedance. Packaged in a single light-weight battery-powered unit, the SD031 complements bridges such as the General Radio 1606, 916, and the Delta OIB-1.
A frequency synthesizer determines the generator frequency, which can be adjusted in 0.5 KHz steps by means of a front-panel switch from 100.0 KHz to 1999.5 KHz. Frequency accuracy is the same as that of the internal reference oscillator. A front panel fine-frequency control varies the frequency up to ± .01 percent. The generator can drive a wide range ofload impedance at levels up to 20 volts RMS. It also has a variable low-level output suitable for driving a counter or for receiver frequency calibration.
The SD-31 uses for detection a coherent detector which rejects interfering signals picked up by the antenna. In this arrangement, the generator is mudulated at a low frequency, and the SD-31 detector circuit responds only to a signal having that particular modulation. A sensitive and selective receiver connected to the bridge detector output is required; this can be the Model RX-31 Receiver, available as an option with the SD-31, or an external receiver such as the Potomac Model FIM-21 Field Strength Meter. The optional RX-31 Receiver is designed to work witht eh SD-31 and is automatically tuned to the generator frequency. The SD-31 is powered by a rechargeable battery adequate for 4-8 hours of use between charges. Battery recharging is possible while the unit is operating.
Technical Specification
Technical Specification
OUTPUTS: VAR Output and Control – varies output level at VAR connector for low level applications
LO Z – high level output for connection to bridge for Z less than 180 ohms.
HI Z – high level output for connection to bridge for Z greater than 180 ohms.
METER FUNCTION SWITCH:
BATT – Indicates charge level of batter supply
LOCK – Provides positive indication that output frequency is locked to crystal reference oscillator frequency
OUTPUT – Indicates relative output of power amplifier
NULL SLOW – Provides highly damped indication of coherent detector output.
NULL FAST – Provides undamped indication of coherent detector output.
AM SWITCH: Selects internal (INT) or external (EXT) Amplitude Modulation of RF output
DET GAIN: Adjusts gain (sensitivity) of coherent detector
FREQ 100.0 – 1999.5 KHz: Sets synthesizer output frequency within indicated range with separate thumb sheel switches for each digit
F CONTROL: Enables operator to vary synthesizer output frequency slightly above or slightly below the nominal value
RX-31 Receiver option
The RX-31 is designed specifically as an RF interface between an impedance bridge and the SD-31 Coherent Detector.
SD-31 Specifications
Frequency: 100.00 – 1999.5 kHz switch selected, 500 Hz steps
Frequency Accuracy: ±005. +200°F to +1000°F
Frequency Vernier (AF) Adjustment Range: ±.01% of frequency approximately
Output Levels:
- HIZ: 20 V RMS with 1000 ohmload (use for Z>180 ohms)
- LOZ: 8 V RMS with50 ohm load (use for Z<180 ohms)
- (HIZ & LOZ: minimum levels with fully charged battery)
- VAR: 100 mV RMS approximately with 50 ohmload
AM Modulation
- Internal: 40 Hz (approximately) square wave
- External: 1.0 mV max. required to produce 50% modulation, 300 Hz – 3 kHz.
Detector Input Requirement (from external receiver)
1 V RMS approximately across 100 K ohms for 100% modulation of receiver RF input at 40 Hz.
Metering (Switch Selected)
- Battery voltage
- Phase loop locking
- Output monitor
- Detector null, fast or slow response
AC Power Unit
105-130 VAC, 50-60 Hz, 15 VA (when charging)
Dimensions
- Height – 9 1/2 inches
- Width – 11 1/2 inches
- Depth – 6 1/2 inches
- Weight – 12 lbs.
Battery Operation Time
- 8 hours approximately after full charge depending on frequency and load.
- 16 hours (unit not in operation)
Specifications subject to change without notice.
