I wanted to use a Retevis HK008 speaker mic with a (tr)uSDX, but without permanently modifying the microphone. The basic problem is simple: the HK008 uses a Kenwood/K1 dual plug — a 3.5 mm plug for speaker audio and a 2.5 mm plug for mic/PTT — while the (tr)uSDX uses two separate 3.5 mm jacks: one for Audio Out and one for Mic/Key.

I chose the external adapter route instead of cutting off the original plug. That way, the HK008 can still be used with other radios.

What I Used

My final adapter was built from:

• a Kenwood/K1 female cable end or extension lead

• one 3.5 mm TRS male pigtail for Mic/Key

• one 3.5 mm TRS male pigtail for Audio Out

• heat shrink tubing

If you want the most durable result, you can also build the adapter into a small rigid block or enclosure. That helps reduce strain on the radio’s PCB-mounted jacks.

The Big Trap: Manual Pinout vs. Real Hardware

This was the part that wasted the most time.

The current official (tr)uSDX documentation shows the Mic/Key jack as:

• Tip = Mic / Audio In

• Ring = PTT / DIT

• Sleeve = GND

And the Audio Out jack as a separate audio output.

However, on my specific unit, real-world testing showed the opposite behavior on the Mic/Key jack:

• Tip behaved as PTT

• Ring behaved as MIC

• Sleeve was GND

So before you build anything, do not assume the printed pinout matches your radio.

The Quick Test That Saves Hours of Frustration

Before wiring the adapter, verify your own radio.

1. Power the radio at low power.

2. With nothing connected to Mic/Key, briefly short:

   • Tip to Sleeve

   • then Ring to Sleeve

3. Watch which one keys the radio.

On my unit:

• Tip to Sleeve keyed TX

• Ring to Sleeve did not

That told me the Mic/Key jack on my unit behaved as:

• Tip = PTT

• Ring = MIC

• Sleeve = GND

If your unit behaves the way the manual says, then wire it that way instead.

What I Measured on the Kenwood Side

After a lot of meter testing, I found the functional pinout on my Kenwood/K1 female side was:

• White = GND

• Black = PTT

• Red = MIC

• Yellow = SPK

This matched what I saw electrically, even though some K1 extension cables use very unintuitive internal wiring.

How to Wire the Adapter

Audio Side

This part is easy.

For the cable going to Audio Out on the (tr)uSDX:

• K1 SPK → 3.5 mm Tip

• K1 GND → 3.5 mm Sleeve

• 3.5 mm Ring can be left unconnected

In my case:

• Yellow → Tip

• White → Sleeve

Mic/PTT Side

This is the part that depends on what your radio actually does.

If your radio matches the printed manual:

• MIC → Tip

• PTT → Ring

• GND → Sleeve

If your radio behaves like mine:

• PTT → Tip

• MIC → Ring

• GND → Sleeve

In my case, that meant:

• Black → Tip

• Red → Ring

• White → Sleeve

All Grounds Should Be Common

This was another important practical lesson.

In the finished adapter, all grounds should be tied together:

• audio ground

• mic ground

• PTT ground

In other words, all Sleeves/GND should be common.

This made the adapter behave much more consistently and helped avoid weird hum or unstable behavior.

Why the Radio Went Into TX by Itself

One of the classic symptoms I ran into was this: as soon as I plugged in the mic, the radio keyed up by itself.

The reason was simple: on my unit, MIC and PTT were effectively reversed from the printed pinout, so the electret mic element ended up sitting on the line the radio interpreted as PTT. The result was a kind of “ghost TX.”

If this happens to you, check these things in order:

1. Verify which contact actually keys TX on your radio.

2. Check for a short between PTT and GND.

3. Verify the 2.5 mm jack or K1 socket is not making bad internal contact.

4. Make sure all grounds are tied together.

Useful (tr)uSDX Settings

Once the adapter works electrically, it also helps to check a few radio settings:

• VOX off

• Keyer mode set correctly for what you are doing

• for SSB, TX Drive and Noise Gate can make a big difference in audio quality

Once the hardware is working, those settings matter a lot more than people realize.

Final Wiring Summary

If your unit behaves like mine

Mic/Key plug to radio:

• Tip = PTT

• Ring = MIC

• Sleeve = GND

Audio Out plug to radio:

• Tip = SPK

• Sleeve = GND

• Ring = not used

Kenwood/K1 side:

• Black = PTT

• Red = MIC

• White = GND

• Yellow = SPK

Actual wiring on my adapter

Mic/Key 3.5 mm TRS plug:

• Black (PTT) → Tip

• Red (MIC) → Ring

• White (GND) → Sleeve

Audio Out 3.5 mm TRS plug:

• Yellow (SPK) → Tip

• White (GND) → Sleeve

• Ring left open

Final Advice

If you want to use a Retevis HK008 with a (tr)uSDX, the adapter itself is not hard to build. The difficult part is not the soldering — it is avoiding the pinout trap.

My advice is simple:

• measure first

• verify the actual Mic/Key behavior on your unit

• then solder

• keep all grounds common

• test at low power first

For me, the working solution was to treat my unit as:

• Tip = PTT

• Ring = MIC

• Sleeve = GND

I would not assume that is universally true for every (tr)uSDX, but it was absolutely true for mine.

So the real takeaway is this:

Do not trust assumptions. Test your own radio first.