US-1

US-1 matching unit in the GSSH-A-18E headset set

The US-1 is a matching unit used with the GSSH-A-18E aviation headset when the headset must be connected to older aircraft communication equipment with a high-impedance audio output. Its main job is to match the receiving audio circuit of the aircraft intercom or radio system with the low-impedance earphones of the headset. In simple terms, without this unit the headset may physically connect to the aircraft, but the sound level in the earphones can be very low. The US-1 corrects this mismatch and allows the headset to work with legacy onboard communication systems.

US-1 with older aircraft intercom systems

The US-1 is especially relevant for aircraft equipped with older communication and intercom systems, including systems such as SPU-7 or similar equipment with high-impedance audio outputs. These systems were designed for a different type of audio load, so direct connection of modern or low-impedance headset phones may not give normal loudness. The matching unit adapts the signal path and helps maintain usable audio volume in the headset. This makes it useful for legacy aircraft, helicopters and training or service environments where older onboard communication equipment is still installed.

Transformer matching inside the US-1 unit

Inside the US-1 there is a matching transformer, commonly identified as TOT-83 in technical descriptions of this device. The transformer changes the impedance relationship between the aircraft audio output and the headset earphones. At the reference frequency, the transformation ratio is specified as 6. This is a passive electrical matching solution, not a digital audio processor or active intercom adapter. The housing is normally treated as non-disassemblable, so repair or modification of the internal transformer circuit is not usually considered a standard line-maintenance operation.

Cable-mounted design of the US-1

The US-1 is made as a compact cable-mounted capsule installed between the aircraft communication socket and the headset cable. One side is fitted with a socket for connecting the headset plug, while the other side has a multi-pin aircraft plug for connection to the onboard communication system. This layout allows the matching unit to remain part of the headset connection harness without changing the headset itself. In supply and replacement, the connector type matters as much as the unit designation, because the same functional adapter may not fit the aircraft if the plug version differs.

US-1 connector arrangement and executions

The standard US-1 arrangement includes a socket such as RVN1-5-2G for connection with the headset cable plug and a four-pin aircraft plug such as ZhF3.645.008-01 for connection to the aircraft side, depending on execution. Several decimal-number versions exist. Some executions include an electrostatic shield, while others do not. Export versions may also be encountered. When ordering, it is better to specify the exact decimal number, required plug type and whether shielding is required. This avoids confusion between visually similar units with different wiring or protection features.

When the US-1 should not be used

The US-1 is not always needed. It is mainly intended for older high-impedance aircraft audio circuits. If the GSSH-A-18E headset is connected to modern civil radios or newer communication systems designed for low-impedance headsets, the US-1 can make the audio worse rather than better. In that case, the matching transformer may reduce volume and introduce an unnecessary interface stage. For radios such as modern Icom, Becker, FL-760 type installations or newer low-impedance aircraft audio systems, compatibility should be checked before using the US-1 in the line.

Identification and supply of the US-1 matching unit

For procurement or replacement, the unit should be identified as US-1 and checked by its decimal number, connector layout and shielding execution. It may be supplied as part of a GSSH-A-18E headset set or as a separate aircraft technical item. Before use, the cable, socket, plug, strain relief, housing condition and continuity should be checked. Since the unit is part of the headset audio path, poor contact or incorrect wiring can cause weak sound, intermittent audio or complete loss of reception in the headset, even when the headset earphones themselves are serviceable.

Product Type: Headset audio matching unit
Designation: US-1
Full Name: Matching Unit No. 1 / First Matching Unit
Associated Headset: GSSH-A-18E aviation headset
Function: Matching of high-impedance aircraft audio outputs with low-impedance headset earphones
Application / Where Used: Aircraft intercom and radio communication circuits using legacy high-impedance audio outputs
Typical Associated Equipment: SPU-7 and similar older onboard intercom / communication systems
Audio Path Function: Reception audio matching for headset earphones
Internal Component: TOT-83 matching transformer
Transformation Ratio: 6 at 1000 Hz
Housing: Compact non-disassemblable cable-mounted capsule
Shielding: Depending on execution; versions with and without electrostatic shield exist
Headset-Side Connector: RVN1-5-2G socket, depending on execution
Aircraft-Side Connector: Four-pin aircraft plug, for example ZhF3.645.008-01, depending on execution
Basic Decimal Number: RX3.849.036, with electrostatic shield
Version Without Electrostatic Shield: RX3.849.036-01
Export Versions: RX3.849.036-02 / RX3.849.036-03
Use with Modern Low-Impedance Radios: Usually not required; may reduce headset volume if used unnecessarily
Technical Documentation: Product passport, headset documentation and aircraft communication system wiring documentation as applicable

All shipments are carried out from our international warehouse in Dubai (UAE), as well as from our partners’ remote warehouses.

In Stock — items available in stock at the Dubai warehouse are dispatched within 5–10 business days after receiving 100% prepayment.

Remote Stock — items available at our partners’ remote warehouses are supplied within an average of 30–45 business days after receiving 100% prepayment.

Pre-Order — made-to-order products are manufactured and delivered within an average of 45–60 business days. Payment terms: 50% advance payment to start production, with the remaining 50% paid before dispatch from the Dubai warehouse after full readiness for shipment.

Returns & Changes (Restocking Fee)
For selected items, a RESTOCKING FEE of 10% may apply in case of return, order cancellation, or changes to the order specifications. This condition applies only to certain products and is confirmed at the order approval stage.

Warranty
All products are covered by a standard 6-month warranty.
Extended warranty is available upon request and is agreed individually; it may affect the final product price.