Transceiver Interfacing

ELAD FDM DUO Transceiver

We have finally completed testing and production of the ELAD FDM DOU to Hardrock-50 interface kit. The unit can be plugged directly into either the radio or the amp and uses a cable (supplied with the kit) to connect to the amp or radio. The kit also includes a 'Y' cable so you can still connect other ELAD peripherals. The kit including the interface board and all of the cables is available here:

The must be set to FT-817 mode in the menu and no changes are needed to the ELAD's set up as long as you have the latest version of ELAD's firmware. I know that some older versions do not send the I2C band data but I'm not sure exactly where the break is. If your radio supports ELADs preselector, it will work with the Hardrock-50 interface.

HobbyPCB IQ32 and RS-HFIQ SDR Transceivers

Technical info about interfacing the Hardrock-50 to the HobbyPCB RS-HFIQ transceiver can be found here.


One of our esteemed Beta testers developed a cable that connects the Hardrock-50 ACC port to the Flex-1500's Flexwire I/O (see Hardrock-50 - Flex-1500 PTT canle.pdf below). We now support automatic band change with PowerSDR software. You will need firmware version 2.0B or higher running in the HR50 so upgrade the firmware if necessary. If you amp is S/N 1199 or lower you will need to modify the rear panel PCB as described in the Band Switching Modifications V2.pdf below. Leave the HR50 connected to the computer's USB port.

When you are updating the firmware, remember the Comm Port number that the HR50 enumerates as because we will need it in the next step. Start PowerSDR, select SETUP and click the CAT Control tab. On the CAT Control frame, select the port that the HR50 uses and if you haven't changed the HR50's USB Baud Rate in the menu, set the baud rate to 19200, then check the Allow Kenwood AI Command box, then the Enable CAT and click OK.

The HR50 will now follow the band selected by PowerSDr.

Starting in late 2017 we updated the rear panel to have an electrically isolated USB connection. This eliminates potential ground loops the cause problems with the Flex-1500 and other SDR's. If you have an older amp, we now provide a update kit to add isolated USB to any Hardrock-50.

Elecraft KX2/KX3

For amps with serial numbers 1200 and above, no modifications is necessary. For earlier amps, the instructions are in the Band Switching Modifications V2.pdf.

If you upgrade to HR50 to Version 3.0 which is available on the  Firmware Update Page, everything you'll need to setup is available via the new menu system.

If you use the PX3 pan adapter you must set the baud rate to 38400.

To enable automatic band switching you must change the following settings in the KX3’s menu:

    AUTO INF – Set for ANT CTRL (causes the KX3 to send frequency data)     
    RS232 – 19200 (could be set to other baud rates as long as the ACC Baud Rate in the HR50 is the same)
    ACCIO2 – ON (enables the PTT output)

On the KX2, the AUTO INF option is found under the TECH SUPPLEMENTAL MENU. To access it, you must set TECH MD prior to ON to be able to set AUTO INFO value to ANT CONTRL. In the spring of 2018, Elecraft released a FW update for the KX3 that put the AUTO INF menu under a TECH menu as well.

The HR50 menus also need to be setup:

    ACC Baud Rate – 19200 (must be the same as the KX3)
    KX3 Serial – Yes (inverts the data coming from the KX3)
    FT-817 Mode – No (FT-817 mode overrides the KX3 mode)

We make a small PCB that plugs into the HR50's ACC jack and provides connections for the KX2, KX3 and the KX-USB cable. The PCB can be found here:

The kit contains everything you need to connect a KX2 or KX3 to the Hardrock-50 amplifier.

Here is the pinout for the KX2's ACC jack:

The connector is a 4 conductor, 3.5mm phono plug.

If you want to make your own KX2 to  Hardrock-50 cable, connect ground to pin 5 on the HR50's DB9, PTT goes to pin 4 and TXD goes to pin 2.
You can find a commercially available cable with right-angle connectors and cut off one end.

Infinite Cables sells one here.

For connections to the HR50's ACC jack, Ground is pin 5, PTT is pin 4 and TXD goes to pin 2. 

For those who wish to roll their own, here is a diagram for wiring the PTT signal from the KX3 ACC2 port and the serial TX data from the KX3 ACC1 port to the HR50's ACC jack. You can also use a inline 3.5MM jack to replicate the KX3's ACC1 port and continue to use all of the computer apps used with the KX3. Down in the files section is a document called How to Build a JX3-HR50 cable which has step-by-step instructions on exactly how to make this cable.

Yeasu FT-817, FT-818

The Yaesu FT-817, 818 is a very popular QRP transceiver and interfaces with the HR50 amplifier for PTT keying and automatic band selection. The FT-817, 818 provides an analog voltage output the level of which indicates the transceivers band setting. The HR50 can read this voltage level and set the amplifier’s band accordingly. If the FT-817, 818 is operating on a band that is not supported but the HR50 (2m and 70cm) the amp will display UNK for the band and remain in bypass.

FT-817 Mode must be enabled in the HR50’s menu to support automatic band selection. HR50 amplifiers with serial numbers below 1200 do not support FT-817 band selection using this technique


The following drawing shows the required connection:

If you want to download the file DO NOT CLICK ON THE FILE NAME!!!

Click on the down-pointing blue arrow on the right side of the page!

Dec 3, 2013, 5:46 PM
Curtis Pope,
Dec 30, 2013, 5:48 PM
Aug 27, 2012, 7:33 PM
Sep 16, 2014, 5:58 AM
Dec 3, 2013, 6:03 PM