Elecraft KX3 + fldigi Setup Guide

KXUSB-A Cable (CAT Control)

• Connectors: 3.5mm plug (ACC1 port on KX3) + Standard USB-A
• Interface Chip: FTDI FT232 USB-to-Serial converter
• Baud Rate: 38400 bps
• PTT Control: Via FTDI handshake (RTS/CTS pins)

Key Connection: Plug 3.5mm connector into ACC1 jack on rear of KX3.

Audio Routing (External Interface)

KX3 Headphone (3.5mm) -> Sound Card Line-In
Sound Card Line-Out -> KX3 Mic Input (3.5mm)

Windows 11/10

Most modern Windows installations automatically install FTDI drivers when you plug in the KXUSB cable.

If manual installation needed: Download from Elecraft Firmware & Software

Critical Issue - COM Port Limitation: Hamlib cannot reliably control the radio if COM port > COM9. Change in Device Manager → Properties → Advanced.

macOS 10.9+

Built-in partial FTDI support. Plug in KXUSB cable and let macOS auto-detect. For advanced features, download from FTDI website.

Linux

Modern kernels include built-in FTDI support via ftdi_sio module.

Verify: lsusb | grep FTDI and ls -la /dev/ttyUSB*

Permissions: sudo usermod -a -G dialout $USER

Start rigctld: rigctld -m 229 -r /dev/ttyUSB0 -s 38400 -v

Rig Control Setup (Hamlib)

1. File → Configure → Rig
2. Check: "Use Hamlib"
3. Rig Selection: Elecraft KX3 (Hamlib model 229)
4. Serial Device:
   • Windows: COM2-9 (NOT higher than COM9)
   • macOS/Linux: /dev/ttyUSB0 or /dev/ttyUSB1
5. Baud Rate: 38400
6. Handshake: RTS/CTS
7. Command Interval: 50-100ms
8. Retries: 2-3 attempts
9. Click "Initialize" - should display KX3 frequency

Audio Configuration

1. File → Configure → Sound Card
2. Capture Device (RX): Select your USB sound card input
3. Playback Device (TX): Select your USB sound card output
4. Sample Rate: 44100 Hz
5. Channels: Mono

Level Setting:

• RX: Adjust so S-meter deflects appropriately
• TX: KX3 ALC meter should show one bar flickering (not constant)

PTT Configuration

Recommended: Use Hamlib for PTT control

1. File → Configure → Modems → Transmit tab
2. Select: "Use Hamlib" for PTT control
3. Keys radio through serial connection (KXUSB cable)

Alternative: VOX - Set fldigi PTT to "VOX" and configure KX3 VOX GAIN menu.

Menu Configuration

Operating Mode

1. Press MODE until "SSB" or "USB" displays
2. Digital modes use SSB as the RF transmission method
3. Do NOT select "PSK-D", "FSK-D", or "RTTY" (radio's internal modes interfere)

Power Settings

Thermal note: KX3 max is 10W. Use 5W for high-duty-cycle digital modes. Monitor temperature during long QSOs.

TX LED Stays On Continuously

• Disconnect all cables from left panel (except power)
• Reduce VOX GAIN menu setting
• Ensure "Mic Button PTT" is OFF
• Restart fldigi and verify serial connection

Hamlib Won't Connect / "Failed to initialize"

• Windows: Verify COM port < 10 in Device Manager
• Verify KXUSB cable firmly seated in ACC1 jack
• Try different USB port on computer
• Restart fldigi after changing settings

TX Audio Too Weak

• Increase Mic Gain dial on KX3 (slowly)
• Increase fldigi TX audio slider
• Check external sound card output level
• ALC meter should show 1-2 bars, not maxed or zero

RF Interference / Erratic Behavior

• Use common-mode choke on antenna coax
• Use shielded audio cables
• Ensure computer and KX3 share common ground
• Use ferrite clamps on USB cables