PDF Brochure - Potomac Instruments

PDF Brochure - Potomac Instruments
SD-31
Frequency Snythesizer
and Coherent Detector
Description
The Model SD-31
Synthesizer-Detector is a highoutput crystal signal generator
of precisely known frequency
combined with a sensitive,
selective detector for RF bridge
measurements of AM antenna
impedance. Packaged in a single
light-weight battery-powered
unit, the SD-31 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 of load 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 modulated 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 with the SD-31 and is automatically tuned to the generator frequency. The SD31 is powered by a rechargeable battery adequate for 4-8 hours of use between charges. Battery recharging is possible while the unit is operating.
Design Features
PI
•
DESIGNED FOR ANTENNA IMPEDANCE MEASUREMENTS WITH RF BRIDGES IN THE PRESENCE OF
STRONG INTERFERENCE
•
HIGH-LEVEL OSCILLATOR COMPATIBLE WITH GENERAL RADIO 1888 SERIES. 818 SERIES, AND DELTA
OIB-1 IMPEDANCE BRIDGES
•
FREQUENCY CRYSTAL CONTROLLED, VARIABLE IN 500 Hz STEPS FROM 100.0 kHz TO 1999.5kHz
•
VERSATILE - CAN BE USED AS AN RF SIGNAL GENERATOR FOR TROUBLE-SHOOTING ANTENNA
SYSTEMS; AS A VARIABLE FREQUENCY OSCILLATOR FOR ANTENNA SITE SURVEY; OR OTHER
APPLICATIONS REQUIRING A PRECISE FREQUENCY SOURCE
•
SPECIAL COHERENT DETECTOR CIRCUIT REJECTS INTERFERING SIGNALS EXPERIENCED DURING
ANTENNA MEASUREMENTS
•
RECEIVER FOR DETECTOR CAN BE EXTERNAL OR OPTIONAL BUILT-IN RX-31 RECEIVER
•
POWERED BY RECHARGEABLE BATTERIES
•
SELF-CONTAINED PORTABLE PACKAGE
Potomac Instruments, inc.
932 Philadelphia Ave./ Silver Spring, MD 20910-4912 / Voice: 1 301.589.2662 / Fax: 1 301.589.2665 / web: www.pi-usa.com
o
METER FUNCTION SWITCH
BATT – indicates charge level of battery supply.
n
p
o
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.
s
q
r
p AM SWITCH
Selects internal (INT) or external (EXT) Amplitude Modulation of
RF output.
q
DET GAIN
Adjusts gain (sensitivity) of coherent detector.
n
OUTPUTS
r
FREQ 100.0 - 1999.5 KHz
VAR Output and Control – varies output level at VAR connector
for low level applications
Sets synthesizer output frequency within indicated range with
separate thumb wheel switches for each digit.
LO Z – high level output for connection to bridge
sUF CONTROL
for ZL less than 180 ohms.
HI Z – high level output for connection to bridge
for ZL greater than 180 ohms
Enables operator to vary synthesizer output frequency slightly
above or slightly below the nominal value.
Instruments, inc.
PI 932 Philadelphia Ave./ Silver Spring, MD 20910-4912 / Voice: 1Potomac
301.589.2662 / Fax: 1 301.589.2665 / web: www.pi-usa.com
Specifications
FREQUENCY
100.00 -1999.5 kHz switch selected, 500 Hz steps
FREQUENCY ACCURACY
±.005, +200oF to +1000oF
FREQUENCY VERNIER (AF)
ADJUSTMENT RANGE
±.01% of frequency approximately
HI Z: 20 V RMS with 1000 ohm load (use for ZL> 180 ohms)
LOZ: 8 V R MS with 50 ohm load (use for ZL< 180 ohms)
OUTPUT LEVELS
}
minimum levels with
fully charged battery
VAR: 100 mV RMS approximately with 50 ohm load
Internal: 40 Hz (approximately) square wave
External: 1.0 mV max. required to produce 50% modulation, 300 Hz - 3 kHz.
Input impedance, 1 Megohm
AM MODULATION
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 INPUT
105-130 VAC, 50-60 Hz, 15 VA (when charging)
DIMENSIONS
Height - 9½ inches
Width -11½ inches
Depth - 6½ inches
WEIGHT
12 lbs.
BATTERY OPERATION TIME
8 hours approximately after full charge depending on frequency and load.
BATTERY RECHARGE TIME
16 hours (unit not in operation)
Specifications subject to change without notice.
RX-31 Receiver Option
The RX-31 is designed specifically as an RF interface
between an impedance bridge and the SD-31 Coherent
Detector. Conveniently mounted in the protective cover of
the SD-31, the RX-31 is a single conversion super
heterodyne receiver which derives its local oscillator signal
and power supply voltage from the SD-31. Receiver
circuitry is packaged in an aperature-free, drawn aluminum
enclosure which provides excellent RF shielding. IF
selectivity is provided by active bandpass filters which limit
receiver bandwidth to 100 Hz.
n
o p
n
RF FILTER
Manually tuned in 3 bands:
o
0.1-0.3 MHz
0.3-0.8 MHz
0.8-2.0 MHz
GAIN CONTROL
Manual with overload indicator.
p
BRIDGE INPUT
100 kHz-1.9995 MHz, automatically set by SD-31.
PI
Potomac Instruments, inc.
932 Philadelphia Ave./ Silver Spring, MD 20910-4912 / Voice: 1 301.589.2662 / Fax: 1 301.589.2665 / web: www.pi-usa.com
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