How to interface your Yaesu FT-817ND/FT-818 radio with a Hardrock-50 HF amplifier

Estimated reading time: 5 minutes

The Yaesu FT-817ND and its successor, the FT-818 is a versatile multi-mode radio covering the ham radio bands 160 – 10 m plus 6m, 2m and 70 cm. However, it’s also a QRP radio with maximum output power limited to 5W. If you want to increase your transmit power the Hardrock-50 HF amplifier (micro build report) is a perfect match, providing > 50W output power from 160 to 6 m. Additionally the Hardrock-50 HF amplifier has an external control port allowing automatic band switching controlled by the connected radio.

I’ve been wanting to control my Hardrock-50 HF amplifier via my Yaesu FT-817ND for quite some time. However, I did not want to build my own cable but insisted on a more professional solution. To accommodate me my friend and fellow ham radio operator Bernhard, DL1MAB designed a nifty FT-817ND hardrock interface adapter. This adapter allows to easily interface a FT-817ND/FT-818 with your Hardrock-50 HF amplifier.

Note: This requires your Hardrock-50 HF Amplifier serial number to be 1200 and higher.

About the Yaesu FT-817ND Accessory Interface

The Yaesu FT-817ND or FT-818 exposes an female Mini-DIN-8 accessory port (ACC) on the backside of the radio which allows to connect the radio to various accessories. For interfacing with the Hardrock-50 HF amplifier PTT (Push-To-Talk), BAND DATA and (obviously) GND need to be connected.

BAND DATA represents the currently selected ham radio band via a stepped voltage:

Connecting the FT-817ND with the Hardrock-50 HF amplifier

The Hardrock-50 HF amplifier exposes an accessory port (ACC) on its rear panel which provides an input pin for PTT (Push-To-Talk) as well as an analog input pin for reading the band information provided by BAND DATA.

After connecting the Yaesu FT-817ND or FT-818 with the Hardrock-50 HF amplifier „FT-817 Mode“ needs to be enabled in order to allow for automatic band switching. Enter the configuration menu by pressing and holding Key/Mode for 2 seconds. Navigate to menu entry #5 – FT-817 Mode – by repeatedly pressing +. Press Key/Mode once to enable adjustment of the parameter. Using +/- change the value from NO to YES. Save changes and exit the configuration menu for pressing and holding Key/Mode for 2 seconds.

Testing the FT-817ND Hardrock Interface

In order to verify the correct functionality of the FT-817ND hardrock interface I’ve created a small test setup in which my trusted Yaesu FT-817ND is connected to my Hardrock-50 HF amplifier (ANT -> IN, ACC -> ACC). A dummy load is connected to the amplifiers output. By going through the bands of the Yaesu FT-817ND as well as transmitting on each band I could verify that the amplifier is following the band changes imposed by the radio.

In the video below the bands of the Yaesu FT-817ND are switched from 160 to 6 m by repeatedly pressing DWN/UP on the transceiver. Due to automatic band switching the Hardrock-50 HF amplifier automatically follows the configuration of the Yaesu FT-817ND transceiver – there is no more need for manually configuring the desired band on the amplifier.

Get your FT-817ND Hardrock Interface

The KiCad files for the FT-817ND Hardrock transceiver interface adapter have been published on GitHub. Furthermore a Aisler project has been created from where you can directly order PCB + parts. There are still a couple of boards lying around from the prototyping phase. If you are interested just write a email or comment below.