N1KDO IOT Band Selector for Elecraft K3 & K4

This project is intended to operate a remote antenna switch.

How is it different than commercial-off-the-shelf solutions?

• Direct interface with Elecraft 15-Pin interface.
• Wireless! It runs over Wifi, no wiring, no lightning arrestors.
• Automatic TX Inhibit prevents TX into wrong/no antenna.
• Cheap cheap compared to existing commercial solutions.
• Open Source Hardware and Software. Do what you will with attribution.

Band Selector

Interfaced with K3

The project is in two pieces:

• The Antenna Switch Controller provides a IOT endpoint for managing a 2x6 or 2x8 antenna switch: https://github.com/n1kdo/AntennaSwitchControl
• The Band Selector interfaces with a K3 or K4 radio, and provides the following functions:
  • Decodes selected bands from Elecraft radio AUX jack.
  • Requests antenna from the controller.
  • If the requested band antenna cannot be selected, activate the radios' TX INHIBIT logic to prevent transmit.
  • The Band Selector includes a 2nd circuit board for the display.

This repository contains the hardware and software for The Band Selector:

• kicad folder contains the electronic design.
• src folder contains the software.
• Bill of Materials

Setup

• Connect the BandSelector to the K3/K4 using the 15-pin "y" cable supplied by Elecraft. Band select data and power status will be communicated to the BandSelector.
• Connect the BandSelector to 10-15 volts DC via the rear panel power jack which accepts a 2.00mm ID, 5.50mm OD coaxial power plug, center positive.

Setup TX Inhibit

If the band selector cannot grant access to an appropriate antenna for the band selected on the radio, it can "inhibit" transmit on the radio, which is useful for protecting the transmitter and amplifier from damage due to antenna mismatch.

When the BandSelector inhibits transmit, the red LED on the lower left of the front panel will light.

The radios must be configured to accept the inhibit input from the Band Selector. Instructions for K3 and K4 are below. The electrical interface from the Band Selector is an "open drain" from a 2N7000 MOSFET

• On a K3, locate the "TX INH" option in the "CONFIG" menu.
  Set this option to "LO=Inh".
  When transmit is inhibited, the "TX" indicator (right side of display, between the A and B VFO labels) will blink.
• on a K4, locate the "TX Inhibit Mode" option in "MENU".
  Set this option to "LO=Inhibit".
  When transmit is inhibited, the TX label (top center of display) will display "TX Inh".

License

The software is licensed under BSD "2-Clause" license, except as where noted.

The hardware is licensed under terms of the Creative Commons Attribution-ShareAlike 4.0 International Public License.