Field · Build · LearnRadio brings people together
Amateur RadioCuriosity · Experimentation · Real connections
The same eight pins, wired six different ways A chart of microphone connector pin assignments. Five amateur radio families and the OHIS standard run down the left, pin numbers 1 to 8 across the top. The cells show which pin carries microphone audio, push to talk and ground. No two rows agree, and the two Yaesu rows differ from each other. THE SAME EIGHT PINS Microphone audio, push-to-talk and ground, as six different products place them on an eight-pin connector. 1 2 3 4 5 6 7 8 PIN 8-PIN ROUND ICOM IC-1201, IC-1271, IC-1275 MIC PTT GND GND KENWOOD TM-201, TM-221, TM-231 MIC PTT GND YAESU FT-840, FT-990, FT-2200 PTT GND MIC YAESU FT-2400, FT-2500 PTT MIC GND 8-POSITION MODULAR ICOM IC-706, IC-706MKII, IC-2000 PTT MIC GND OHIS v0.3 the proposed standard 5V PTT MIC G HP L HP G MIC PWR G HP R microphone audio push-to-talk ground accessory power headphone audio not used / not published Radio pin assignments from the Tigertronics radio wiring table. OHIS row from the Open Headset Interconnect Standard v0.3. The model families shown are examples, not every radio a manufacturer has shipped.
Six products, one eight-pin connector, six different arrangements. The two Yaesu rows are the argument in miniature: mic audio on pin 8 in one family and pin 4 in another, from the same manufacturer. Radio pin assignments from the Tigertronics wiring table; the OHIS row from the standard itself.

Articles Interfaces

Opinion

The plug fits.
The wiring does not.

Amateur radio needs a standard microphone and headset interface. QEX said so in 1999. Twenty-five years later we still cannot move a microphone between two radios without checking a chart.

By Tony Pelfanio, K4DIASeptember 2026About 6 minutes

Many amateur radios appear to use the same microphone connector. Some have an eight-pin round connector. Others use an eight-position modular connector, commonly called RJ-45. A good number of mobiles, including most of the current Yaesu FTM line, use a six-position modular plug instead, which looks like a telephone lead and is not interchangeable with either of the others.

The plugs may physically fit. The wiring can be completely different.

Depending on the manufacturer or the model, microphone audio may be on a different pin. PTT may operate differently. A pin may carry 5 or 8 volts. Grounds may be combined or separated. The radio may expect a dynamic or an electret element. Receive audio may be at speaker, headphone or line level. Control functions may share pins with audio or power.

Connect the wrong microphone and you can get distorted audio, an unwanted transmission, a shorted accessory supply, or a damaged radio.

Why are we still accepting this?

This problem is decades old

In the January and February 1999 issue of QEX, Lawrence G. Dobranski, VA3LGD, argued for standard application-programming interfaces in amateur radio. Making the case that manufacturers were unlikely to agree on anything, he reached for the most obvious example to hand: Given the ham-radio equipment manufacturers' inability to agree on the wiring of the microphone connector, the possibility of getting a standard command set developed…1

He used it as a throwaway line. Everybody already knew. That was more than twenty-five years ago.

Since then radios have gained spectrum displays, digital signal processing, USB, Ethernet, Bluetooth, Wi-Fi, remote operation and software-defined receivers. We still cannot safely move a microphone from one radio to another without checking a wiring diagram.

Tigertronics puts it plainly on its own wiring page: There seems to be a total lack of standardization for pin-outs on mobile and base station mic connectors. There is even a lack of consistency within the same manufactures models in some case.2 Their table backs it up. Look at the two Yaesu rows in the chart at the top of this page. The FT-840, FT-990 and FT-2200 put microphone audio on pin 8. The FT-2400 and FT-2500 put it on pin 4. Same manufacturer, same eight-pin shell, different wiring.

West Mountain Radio builds configurable jumpers into its RIGblaster interfaces for the same reason, and says so on its own support page: Other radios, such as Yaesu and Kenwood, with 8 pin round microphone connectors would have different jumpering diagrams because they use different pin numbers in the microphone cable assigned for these functions.3 That is a manufacturer designing around the problem rather than a customer complaining about it.

Heil Sound runs a compatibility finder where you pick your radio manufacturer, then your model, then whether you want a headset or a microphone, and it tells you which adapter cable you need.4 There are separate guides for Icom, Kenwood, Yaesu, Elecraft, Flex, Ten-Tec and the vintage Collins and Drake gear.

The adapter market is not a solution to the problem. It is the evidence of it.

I run into this constantly

I have several handsets and microphones I would like to use across different radios. Every time I connect one, I have to find the pinout, work out the element type, check for bias voltage, establish how PTT is switched, and then build or rewire another adapter.

Even when two radios use the same connector, I cannot assume the wiring matches. That defeats the entire purpose of a common connector.

The functions involved are not exotic:

  • Microphone audio
  • Speaker or headphone audio
  • Push-to-talk
  • Ground
  • Limited accessory power
  • Optional controls

The industry simply never agreed on where these signals go or how they should behave.

Adapters are a workaround

An adapter solves one radio and one microphone. It does not solve the problem.

An operator using one headset with Icom, Yaesu and Kenwood radios may need three different adapters. Add another headset, a digital interface or a fourth radio and the combinations multiply.

This gets expensive and fragile in exactly the places it matters most: club stations, Field Day, emergency operations centres, multi-operator contest stations, portable kits, and any shared radio room. Every adapter is another cost, another cable, another label and another thing to fail at two in the morning.

A volunteer arriving at an emergency communications station should be able to plug in a headset. Not dig through a box of adapters, and not wonder whether this particular radio puts 8 volts on the pin their microphone uses for audio.

Interoperability should be built into the equipment.

One standard does not mean one connector

Standardising does not mean bolting the same full-size connector onto every radio. Handhelds, compact SDRs, mobiles and base stations have genuinely different constraints.

A workable system would define connectors by equipment class:

  • Handhelds. A standard 3.5 mm TRRS, or the Kenwood K1-style two-plug arrangement, carrying microphone audio, speaker audio and PTT.
  • Compact SDR and QRP radios. The same small connector standard where panel space is tight.
  • Mobiles. A shielded eight-position modular connection carrying audio, PTT, accessory power and basic controls.
  • Base stations. The same shielded eight-position modular connection as the operator interface, on the front panel and the rear.
  • Field equipment. A ruggedised locking shell such as etherCON, carrying the identical electrical arrangement.

The physical connector changes with the size and purpose of the radio. The electrical behaviour stays the same. An adapter between two approved connector sizes should then be a straight one-to-one connection, not a different wiring diagram with a resistor and a voltage conversion for every radio.

An open standard already exists

We do not have to start from nothing. The Open Headset Interconnect Standard, OHIS, is a community-developed specification from Mark Smith, N6MTS, and Tom Tengdin, WB9VXY. Version 0.3 is dated 16 May 2023.5

It defines all eight positions on a shielded modular connector, shown in the bottom row of the chart above: accessory power on 1, PTT on 2, microphone ground on 3, headphone left on 4, headphone ground on 5, microphone audio on 6, power and PTT ground on 7, headphone right on 8, with the shield tied to power ground.

More importantly, it specifies behaviour rather than just pin positions. The microphone is an electret at roughly −45 dBV into 600 to 1000 ohms, biased at about half a milliamp. Accessory power is a regulated 5 volts at 200 milliamps. Neutrik's etherCON is named as the rugged option, and it stays compatible with ordinary RJ-45 leads.

Under this approach each older radio gets one adapter that lives with the radio, and each headset gets one adapter that lives with the headset. After that, any compliant headset works with any compliant radio. Ham Radio Workbench covered OHIS with N6MTS in episode 167 in November 2022.6

OHIS may not turn out to be the final answer. It is a serious starting point, and it is further along than anything the manufacturers have offered.

Keep the advanced controls separate

Modern hand microphones carry frequency controls, DTMF keypads, programmable buttons, displays and digital signalling. None of that prevents basic standardisation.

A common interface has to guarantee four things: safe and dependable audio, PTT, grounding, and accessory power. Manufacturer-specific functions can live on a separate digital extension, or stay on the original factory microphone connector where they already work.

A universal headset does not need every button on a factory hand microphone. It needs to pass audio and key the transmitter without putting the radio at risk.

What needs to happen

  1. Agree standard microphone levels and bias voltage.
  2. Define one safe method of activating PTT.
  3. Set voltage and current limits for accessory power.
  4. Define grounding, shielding and equipment protection.
  5. Adopt practical connectors for handheld, mobile, base and field equipment.
  6. Publish complete specifications and open adapter designs.
  7. Fit a standard rear-panel connection to new radios.
  8. Offer adapters for existing equipment.

The standard should stay open, so anyone can build a compatible microphone, headset, foot switch, interface or adapter.

It is time to fix it

Nobody is suggesting we throw away working radios. Older equipment can stay in service with an adapter. The question is why a radio designed today should repeat the same incompatibility.

A modern transceiver can work satellites, display an entire band, decode digital modes, join a network and update its own firmware. Its microphone should not need a wiring chart because the operator changed brands.

The plug should fit. The wiring should match. The equipment should be safe. It is time amateur radio adopted a real microphone and headset standard.

References

  1. Lawrence G. Dobranski, VA3LGD, The Need for Standard Application-Programming Interfaces (APIs) in Amateur Radio, QEX, January and February 1999. Source of the quotation on microphone connector wiring. arrl.org (PDF)
  2. Tigertronics, Radio Wiring Information. Source of the quotation on the lack of standardisation, and of the Icom, Kenwood and Yaesu pin assignments shown in the chart above. tigertronics.com
  3. West Mountain Radio, Why we use jumpers inside RIGblasters. Source of the quotation on Yaesu and Kenwood eight-pin round connectors using different pin numbers. westmountainradio.com
  4. Heil Ham Radio, Product Compatibility Guide. Adapter cable and headset finders selected by radio manufacturer and model, with per-manufacturer guides for Icom, Kenwood, Yaesu, Elecraft, Flex, Ten-Tec and vintage equipment. heilhamradio.com
  5. Open Headset Interconnect Standard, version 0.3, 16 May 2023, by Mark Smith, N6MTS, and Tom T. Tengdin, WB9VXY. Source of the pin assignments, the electret and bias figures, the 5 volt 200 milliamp accessory supply and the etherCON reference. ohis specification (PDF) · ohis.org
  6. Ham Radio Workbench, episode 167, Open Headset Standard Interface with Mark N6MTS, November 2022. hamradioworkbench.com

The chart at the top of this page is drawn from the sources named in it and covers the model families listed, not every radio a manufacturer has shipped. Check the manual for your own radio before wiring anything.