Potomac Instruments PI-4100 Field Strength Meter


The PI-4100 is Potomac’s third generation of precision survey instrumentation intended for the direct measurement of electromagnetic field strength in the 520 kHz to 5.1 MHz frequency spectrum. This instrument combines a laboratory quality radio frequency voltmeter, a calibrated, shielded loop antenna, an internal GPS receiver, an internal calibration source, and data acquisition hardware and software in a single rugged package weighing less than 3 kg.

This device is equipped with an embedded microcontroller engine that obtains measurement data from the various transducers within the instrument and formats that data for display and, at the option of the use, stores it to memory.


The PI-4100 was designed to become the successor to the industry standard FIM-41 and to provide the accuracy and reliability that has been depended upon by the international engineering community, government regulators, and broadcast licensees for more than a generation.

PI-4100 innovations include:

  • 116 dB dynamic range tuned RF voltmeter
  •  Digitally synthesized tuning in 1.0 kHz increments
  • Spectrum display to facilitate various compliance measurements (Field Strength, Harmonic level, and Spectrum Occupancy) in a single instrument
  • Provisions for third party calibration – using their laboratory standards – when it is impractical to return the instrument to the manufacturer for calibration
  • Data acquisition software and PC interface to enable the collection, analysis, and e-distribution of current field measurements. (This feature anticipates the future acceptance of data e-filing by federal regulatory agencies.)

Various I/O ports have been provided to enhance the versatility of the instrument and to perform certain operational tasks such as battery recharge and computer data exchange.

Technical Specification

Technical Specification

Field Strength Meter
Frequency Range 520 kHz to 5.1 MHz, calibrated
Field Strength Range 22 µV/M to 50 V/M (27 dBuV/m) to 154 dBuV/m)
Measurement Uncertainty 3.0% (±0.3 dB) referenced to NIST*, standard field
Measurement Bandwidth
Adjacent Channel Rejection
Image Rejection   Spurious Rejection
1.0 kHz>85 dB at ±9 kHz>60 dB>80 dB
Minimum Frequency Step 1.0 kHz
Self generated 2nd & 3rd harmonics <-85 dBc (carrier F/S <10 V/M, from 530 to 1700 kHz)
Antenna Type Balanced, multiturn Loop (removeable)
RF Voltmeter
Electrical specifications shown above RF Signal is applied directly to RF In BNC
Measurement Units µV-mV-V; mV only; dBuV/m
Spectrum Display
Center Frequency Range 520 kHz to 5.1 MHz
Frequency Span ±63 kHz, ±22 kHz
Resolution Bandwidth 1 kHz
Data Storage & Retrieval
Measurement Points 250 max.
Download Software PI Proprietary (Microsoft Excel® format compatible)
Download Format ASCII: Comma Delimited
I/O Ports
Headphone Jack 3.5 mm Stereo Audio Jack
Battery Charging Jack (12-15 Vdc) 2.1 mm Power Jack (Switchcraft 722A or equiv.)
Data output / Control Input Jack USB Type B (for bi-directional computer interface)
External RF Calibration Jack BNC (provides for calibration by a 3rd party cal. lab.)
External RF Input Jack BNC (input impedance 1890 ohm +12pF) provides for antenna signal injection
External RF Output Jack BNC (50 ohms) RF output is proportional to Field Strength
Batteries (AA cells, six required) Rechargeable; NiMH (supplied)(can also use 1.5V: Alkaline or Lithium)
Battery Life 5 Hrs. Minimum before Recharge (NiMH)
Battery Recharge Time 3 to 4 Hours
Operating Temperature Range °C(°F) -15°C to +50°C (+5°F to +130°F)
Dimensions cm (inches) 38x18x28 cm (15x7x11 in.)
Weight kg (lbs.) 2.5 (5.5)

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