Embedded Files
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.
If you are running the latest FW or a HR50+, select KX2/3 in the transceiver menu and set the ACC baud rate the same as the KX3. If you are using the PX3 the baud rate must be 38400. If you have older FW, 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/Xiegu Mode – No (FT-817 and Xiegu modes overrides the KX3 mode)
In the latest firmware, V4 and later, there is a transceiver selection menu item so you won't need to find the FT817 or Xiegu entries, just select KX2/3 in the menu.
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:
https://www.hobbypcb.com/products/hf-radio/kx2-kx3-hardrock-50-interface
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.
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