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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.

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Field Strength Meter FIM 72A UHF
enlarged view


KEY FEATURES
  • 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