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Field Strength Meter
FIM-72A UHF
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DESCRIPTION
The Model FIM-72A is a portable, laboratory quality Field Strength
Meter designed for rigorous field applications. Combining a calibrated
half-wave dipole antenna and a highly accurate tuned voltmeter with
a range of 140 dB, the FIM-72A is suitable for practically all types
of RF emission measurements in the 450 MHz to 960 MHz spectrum. The
operator can switch select wide or narrow bandwidth, peak or average
value of TV or pulse modulated signals, AM or FM demodulation, and
meter dynamic range of either 20 dB or 60 dB. A dc analog voltage,
proportional to meter indication, is provided for driving a chart
recorder or similar device. A leveled output from the calibrating
generator is available for measuring cable insertion loss, filter
response, amplifier gain, VSWR, and other signal ratio measurements.
The 4-1/2 inch, taut band, mirrored scale meter is calibrated in volts
and dB for precise measurements in field or laboratory environments.
The tuned voltmeter is a double conversion, super-heterodyne receiver
with carefully tailored sensitivity, selectivity, gain, and linearity
characteristics. The RF input includes preselection designed for minimum
VSWR and maximum out-of-band signal rejection. Uniform gain, independent
of IF bandwidth, is provided by temperature compensated RF & IF amplifiers
utilizing a combination of MOSFET, bipolar, and monolythic integrated
circuit devices. The linear detector is followed by a logarithmic
shaping circuit which drives the meter in the LIN (20 dB) mode. In
the LOG mode DC feedback is applied to the receiver in such a manner
that the meter indication (in dB) varies linearly over a one-thousand-to-one
range of input levels. |
| FIM-72A
SPECIFICATIONS |
| Frequency Range |
450 MHz - 960 MHz; continuous |
| RF Input Impedance/VSWR |
50 ohms
VSWR/1.2:1 max, 100µV full scale and greater;
VSWR 2.0:1 max, 10µV full scale; BNC connector |
| Voltage Measurement |
1µV to 10 V rms in seven switch-selected
ranges |
Metering
Indication Modes
Scales |
4-1/2 inch meter, mirror-backed scale
LIN (linear) and LOG (with receiver dc feedback), switch selected
LIN Scales: 1-10 logarithmic and 0-20 dB linear;
LOG Scale: -20 to +40 dB linear (60 dB range)
Battery voltage/external supply voltage scale |
| Metering Detectors |
Average responding and Peak-responding
(for television sync pulse), switch selected |
| Receiver Bandwidths |
AM/FM 190 kHz at -3 dB, and
TV, 450 kHz at -3 dB, switch selected |
| Absolute Accuracy |
Voltage: ±1.5 dB (LIN),
±2.0 dB (LOG), for voltage >1.5µV (AM/FM) or >3µV
(TV)
Field Strength: ±3.0 dB (LIN), ±3.5 (LOG) for
field strengths>19µV/M (AM/FM) or >38µV/M (TV) at 450
MHz; >39µV/M (AM/FM) or >77µV/M (TV) at 960 MHz; using
the ANT-72 Antenna |
| Note: These figures apply when
using the Average Detector; for the Peak Detector, noise correction
factors (supplied) are required below 10 mV |
| Relative Accuracy |
±1 dB at one frequency, for
voltage or field strength, LIN mode, for voltage>10µV, with
noise correction factors |
Calibrating Oscillator
Output Level & Accuracy |
Output switched to receiver for internal
calibration (CAL Mode), or to external BNC connector (GEN OUT Mode).
Generator frequency tracks receiver frequency.
100mV±0.3 dB across 50.0 ohms |
Frequency Dial
Accuracy |
Six-turn spiral, continuous tuning,
movable cursor (45 MHz to 225 MHz)
±0.5% of indicated frequency without cursor correction |
| Automatic Frequency Control |
Switch selected; frequency-locks receiver
to received signal; Lock Range ±5MHz min. (internally adjustable)
|
| RCVR Spurious Response |
Image Rejection, 55 dB typical;
IF Rejection, 100 dB typical |
| Local OSC Radiation |
45 MHz, 2µV; 225 MHz, 35µV;
typical values across 50 ohm load at RF input connector |
Demodulators
Video Frequency Response
Output Level |
AM and FM; switch selected, phone
jack (0.25") output connector
50 Hz - 100 kHz, 3 dB max. variation
4.5V p-p max. across 75-ohm load, variable by AUDIO control |
| Audio Monitoring |
Internal loudspeaker; headphones plug
into demodulator output jack (disconnecting speaker);
AM or FM selected by DEMOD switch; level control with disabling switch |
Record Output
Tip Contact
Ring Contact |
Two-circuit phone jack (0.25")
output,
DC analog of meter indication 0.8V - 8V open circuit, 2000 ohm source
resistance
DC output from FM discriminator, @ -5 ±3V, 10,000 ohm source
resistance,
(Single circuit phone plug provides tip contact output only.) |
Power Supply:
Internal Batteries
Battery Life
External Supply |
1.5 volt size "D" batteries, ten required
800 readings or 18 hours continuous operation using Eveready No. E95
(alkaline) batteries at 70°F
11.5 volts to 16 volts DC, positive ground, 360 mA, Switchcraft No.
760 Connector (or equivalent) |
| Temperature Range |
+15°F to +105°F (-10°C
to +40°C) |
| Dimensions, Inches (CM) |
Without Antenna: 9.5 (24) high, 12.25
(31) wide, 7.25 (18.4) deep
With Antenna attached and retracted, 9.9 (25) high, 13.5 (34.3) wide,
7.25 (18.4) deep |
| Weight, Pounds (KG) |
20 (9.1) with batteries, antenna,
cover, cables and softcase |
| Note: Values without limits are typical only.
Field strength data with ANT-71 Antenna. |
| Antenna Ant-71 |
| Type: |
Tunable half-wave dipole with continuously
adjustable telescoping elements with balun |
| Frequency Range:
|
450 - 960 MHz |
| Calibration: |
Antenna Factor data supplied based
on NIST calibration; overall error including NIST calibration uncertainty,
±1.5 dB max |
| Load Impedance: |
50 ohms |
| Mounting: |
Mounts on FIM-72A case for hand-held
measurements at an antenna height of approx 7 ft.; has 1/4-20 threaded
hole for mounting to other masts |
Specifications subject to change without notice.
|
- Direct Reading - Volts or dB
- 450 MHz to 960 MHz, Continuous Tuning
- Peak or Averaging Detector
- Wide or Narrow IF Bandwidth
- 20 dB or 60 dB Meter Range
- AM or FM Demodulator
- Calibrated Dipole Antenna, Case Mount or Removable
- 140 dB Measurement Range
(1 uB to 10 V)
- 4-1/2 inch, Mirrored Scale, Taut-Band Meter
- Front Panel Speaker
- Rugged, Portable
- Calibrated Signal Generator
OPTIONS
- AC Power Adapter
- Unipod
- Carrying Case
- Antenna Elements and Balun
- Headset
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