AL-RS101-SET MIL-STD-461 RS101 Transmit/Receive Loop Antenna Set

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AL-RS101-SET Transmit/Receive Loop Antenna Set — Frequently Asked Questions

1. What is the Com-Power AL-RS101-SET and what is it primarily used for?
The AL-RS101-SET is a matched transmit/receive passive loop antenna pair purpose-built for MIL-STD-461 RS101 radiated susceptibility (magnetic field) testing from 30 Hz to 100 kHz. The set consists of the AL-RS101-TX transmit loop — which generates a known magnetic field to expose the EUT — and the AL-RS101-RX receive loop — which calibrates the generated field level before and during the test. Together they let a lab verify the magnetic-field immunity of military equipment against interference from magnetic sources such as onboard generators, propulsion systems, power converters, and transformers.

2. What are the key specifications of the AL-RS101-TX transmit loop?
Frequency: 30 Hz – 100 kHz. Mean loop diameter: 12 cm. Turns: 20. Wire: 12 AWG enamel-insulated copper — heavy gauge required to carry the test current continuously. Resistance: 40 mΩ nominal. Inductance: 60 µH nominal. Max continuous current: 15 A. EUT spacing: built-in 5 cm via elongated Teflon (PTFE) structure. Connectors: two banana jacks for amplifier drive. Weight: 2.2 lbs (1 kg). Construction: Teflon coil form (heat-resistant, low-loss dielectric) wound with enamel-insulated copper for handling sustained high current without insulation breakdown.

3. What are the key specifications of the AL-RS101-RX receive loop?
Frequency: 30 Hz – 100 kHz. Loop diameter: 4 cm. Turns: 51. Wire: 7-strand 41 AWG Litz wire (low AC resistance). Shielding: electrostatic shield with gap (E-field rejection, magnetic flux transparent). Resistance: 4 Ω nominal. Inductance: 180 µH nominal. Connector: BNC female. Weight: 0.26 lbs (0.12 kg). The RX loop is much smaller than the TX loop because it only needs to sample the field at a calibration point — the small size gives a sharper, more localized measurement.

4. What is MIL-STD-461 RS101 and why does it require a transmit/receive loop pair?
RS101 is the MIL-STD-461 requirement for radiated susceptibility to magnetic fields from 30 Hz to 100 kHz. Unlike E-field immunity tests that use horn or biconical antennas driven by power amplifiers, RS101 uses a driven current loop to generate a known magnetic field intensity at the EUT. A separate receive loop is mandatory because (a) driving current into the transmit loop does not directly tell you the field strength at the EUT — that depends on geometry and loop impedance; (b) pre-test and during-test verification of field level is required; and (c) the standard specifies a dedicated calibration procedure using the RX loop in a prescribed fixed position relative to the TX loop.

5. Which standards and agencies accept the AL-RS101-SET?
• MIL-STD-461 (all revisions C through G) RS101 radiated susceptibility magnetic field
• U.S. Navy shipboard platforms — the most common RS101 driver, where onboard propulsion motors, generators, and degaussing systems produce strong low-frequency H-fields
• U.S. Army ground vehicles and tactical platforms
• U.S. Air Force and NASA airborne and space-flight equipment where applicable
• DoD contractor requirements on military electronic equipment
• SAE ARP-958 calibration methodology (applied to the RX loop)
• Commercial magnetic-immunity pre-screening for products that must survive low-frequency magnetic environments (e.g., medical imaging systems, industrial motor-drive environments)

6. How does the RS101 test actually work, and where does each loop go?
The procedure has two phases:
• Phase 1 — Test-level calibration: The AL-RS101-RX receive loop is mounted in a fixed, standard-specified position relative to the AL-RS101-TX transmit loop using the supplied mounting arrangement. A power amplifier drives the TX loop with an increasing current until the RX loop’s output voltage corresponds to the required test field strength — this establishes the amplifier drive level for that frequency.
• Phase 2 — EUT exposure: The TX loop is positioned against the EUT with the built-in 5 cm Teflon spacer touching the EUT surface, the amplifier is set to the previously calibrated drive level, and the EUT is exposed to the generated H-field. Any malfunction, degradation, or anomaly during exposure is a susceptibility failure.
The calibration process uses the RX; the actual EUT test uses the TX. That is why the set includes both and why they must be a matched pair with known characteristics.

7. Why does the AL-RS101-TX use 12 AWG solid copper while the AL-RS101-RX uses Litz wire?
The two loops have opposite requirements:
• TX loop must carry 15 A continuous to generate the required field strengths. Solid 12 AWG enamel-insulated copper has very low DC resistance (~1.6 mΩ/m) and high continuous current capacity; enamel insulation with a Teflon structure gives thermal safety margin. Litz wire would not handle this current for sustained dwell times — its many thin strands don’t collectively carry 15 A without overheating
• RX loop only carries receive-level signal currents (microamps), so current capacity is irrelevant. What matters is low AC resistance for low thermal noise and consistent response across 30 Hz–100 kHz. Litz wire mitigates skin and proximity effects to give flat, low-loss response. The 7-strand 41 AWG Litz is the same wire type used in the AL-RE101 receive loop for the same reasons

8. Why does the AL-RS101-TX include a built-in 5 cm Teflon (PTFE) spacing structure?
MIL-STD-461 RS101 requires the transmit loop to be placed with a specified 5 cm spacing between the loop plane and the EUT surface. The AL-RS101-TX is wound on a Teflon (PTFE) structure that is elongated — the coil form physically extends the loop plane outward from the base, so when the base is set flush against the EUT, the loop sits exactly 5 cm away. Teflon is chosen because it has (a) excellent high-temperature stability (important when the coil dissipates I²R heating at 15 A), (b) very low dielectric loss (doesn’t absorb RF energy), and (c) chemical inertness for long-term durability in lab environments.

9. What amplifier do I need to drive the AL-RS101-TX for RS101 testing?
RS101 requires a high-current, low-frequency power amplifier capable of delivering up to 15 A continuous into the low impedance of the TX loop (40 mΩ + jω·60 µH). Considerations:
• Frequency range: 30 Hz – 100 kHz — a specialized audio or LF power amplifier, often with current-mode operation
• Output: must deliver high current into a very low impedance load, which a standard 50 Ω RF amplifier cannot do without a matching transformer
• Continuous power: at 15 A through ~40 mΩ + series impedance, continuous dissipation in the loop is modest (~9 W), but the amplifier must sustain the current level throughout the test dwell
• Protection: amplifier should tolerate the inductive load without oscillation or shutdown
Com-Power and specialty EMC vendors offer amplifiers designed for RS101 drive; general-purpose audio amplifiers may work at the lower end of the band but often cannot sustain current at 100 kHz.

10. What real-world products and systems use AL-RS101-SET testing?
• Naval shipboard electronics — exposure from onboard propulsion motors (thousands of amps), generators, degaussing coils, and magnetic anomaly detection systems
• Submarine electronics — very strong magnetic environments from propulsion and ballast systems
• Military ground vehicles — electric drivetrain, battery management, motor controllers
• Aerospace platforms — verifying flight-critical electronics immunity to onboard magnetic sources (generators, actuators)
• Hall-effect sensors, magnetoresistive sensors, magnetometers — sensitive to low-frequency magnetic interference by design
• CRT displays and magnetic storage — where magnetic interference causes image distortion or data corruption
• Compass and navigation systems — immunity verification during qualification
• Medical imaging — pre-screening electronics for MRI-adjacent service environments
• Repair/requalification testing — verifying that repaired or upgraded military gear still passes RS101

11. How does the AL-RS101-SET compare with other Com-Power loop antennas?
• vs. AL-RE101 (30 Hz–100 kHz, single loop): AL-RE101 is receive-only for MIL-STD-461 RE101 emissions; AL-RS101-SET transmits and calibrates for MIL-STD-461 RS101 susceptibility. Opposite directions of the same test program — often owned together for a full MIL-STD-461 low-frequency magnetic suite
• vs. AL-130R (active loop, 9 kHz–30 MHz, CISPR): AL-130R is a commercial active loop for emissions site surveys; AL-RS101-SET is a military passive transmit/receive pair for susceptibility. Different standards, different functions entirely
• vs. ALT-930-2M (Van Veen triple loop, 9 kHz–30 MHz): ALT-930-2M is a large 2-m three-axis receive system for CISPR 15 lighting equipment emissions; AL-RS101-SET is a small close-proximity transmit/receive pair for MIL-STD-461 RS101 susceptibility. No application overlap
• vs. AM-741R (active monopole, 9 kHz–30 MHz): monopole measures E-field; AL-RS101-SET generates and measures H-field. Complementary for full MIL-STD-461 coverage

12. How is the receive loop (AL-RS101-RX) used for test-level calibration?
The AL-RS101-RX is mounted on the AL-RS101-TX in a fixed, prescribed position using the supplied mounting arrangement — this geometry is defined by MIL-STD-461 so that the RX loop samples a known fraction of the TX field. The RX loop’s BNC output connects to an EMI receiver or RF voltmeter. The amplifier drives the TX loop until the RX output voltage reaches the value that corresponds to the required field strength (e.g., for a 20-A/m test level, the RX voltage is read from the SAE ARP-958 calibration data for that frequency). This drive level is then noted and applied during EUT exposure. The RX loop is removed during actual EUT testing — it only participates in the calibration phase.

13. Why is SAE ARP-958 calibration critical, and what does NIST-traceable mean?
SAE ARP-958 is the aerospace industry’s recognized method for calibrating magnetic-field loop antennas — it defines how to derive transfer factors (A/m per volt or similar) from measurement of loop response. Every AL-RS101-TX and AL-RS101-RX is individually calibrated per SAE ARP-958 using NIST-traceable equipment. Without accurate calibration, you cannot know the actual field strength the EUT sees — and the RS101 test becomes meaningless for compliance evidence. NIST traceability is an unbroken documented chain of calibrations back to the U.S. National Institute of Standards and Technology primary standards. ISO 17025 accredited calibration is available on request when your lab’s accreditation body requires an externally audited certificate.

14. What are common measurement pitfalls with the AL-RS101-SET and how do I avoid them?
• Incorrect amplifier — a 50-Ω RF amp will not deliver 15 A into a low-impedance loop; use a purpose-built LF current amplifier or specialty RS101 driver
• Insufficient amplifier headroom at the upper band — 100 kHz into a 60 µH inductance is jωL = j37.7 Ω, raising the drive voltage requirement significantly at high frequency
• Ambient ground loops — the low-frequency measurement is sensitive to ground-loop hum; use a well-bonded single ground reference
• TX and RX loop separation errors — use the supplied fixed mounting arrangement; do not improvise geometry
• EUT positioning — flush 5 cm contact with the Teflon spacer must be maintained during exposure; any gap changes the actual field strength
• Thermal drift — at 15 A continuous, the TX loop warms slightly; factor a brief thermal stabilization before calibration readings
• Connector torque and cleanliness — verify banana-jack connections are tight and oxide-free; high-current joints must be low-resistance

15. What are the AL-RS101-SET’s key design advantages?
• Purpose-built for MIL-STD-461 RS101 — exact geometry and construction per the standard’s requirements
• Matched transmit/receive pair with fixed mounting arrangement for accurate test-level calibration
• AL-RS101-TX: 12 cm mean diameter, 20 turns, 12 AWG copper, 15 A continuous, built-in 5 cm PTFE spacer
• AL-RS101-RX: 4 cm diameter, 51 turns, 7-strand 41 AWG Litz wire, electrostatic shield, BNC female
• Teflon coil form on TX — high-temperature stable, low-loss, chemically inert
• Banana-jack TX connectors — simple, low-resistance interface for high-current amplifier connections
• Electrostatic shield on RX — rejects E-field so only magnetic field is measured
• Individual SAE ARP-958 NIST-traceable calibration for both loops; ISO 17025 available
• Lightweight: TX 2.2 lbs, RX 0.26 lbs — easy to move and position
• Passive (no preamplifier, no battery) — unlimited dynamic range, no maintenance
• 3-year standard warranty

16. When should engineers select the AL-RS101-SET over other Com-Power antennas?
Select the AL-RS101-SET when any of the following applies:
• You are performing MIL-STD-461 RS101 radiated susceptibility (magnetic field) testing at any revision
• Your program is Navy shipboard, where magnetic immunity is especially critical due to strong onboard H-fields
• Your program is Army ground vehicle, Air Force airborne, or aerospace with RS101 flowdown requirements
• You are a defense contractor delivering equipment to DoD or prime contractors
• You are verifying Hall sensor, magnetoresistive sensor, magnetometer, or CRT display immunity to magnetic interference
• You need to requalify repaired or upgraded military equipment against RS101
• You are performing design-phase immunity debug of electronic systems intended for magnetic-heavy environments
Choose the AL-RE101 if you need to measure magnetic emissions per RE101 (emissions testing, not susceptibility). Choose the AL-130R for active-loop commercial CISPR H-field site surveys. Choose the ALT-930-2M for CISPR 15 lighting-equipment three-axis magnetic emissions.