Switch Hardware
The hardware was designed to do antenna switching. It handles all of the time critical functions.
There are several versions of the hardware available from different sources. Some of them use different connectors, different USB chips, and may have simultaneous high and low side outputs.
This documentation describes the M1DST hardware.
The switch receives power through an Anderson PowerPole™ connector.
The board is intended to run from 13.8 volts, but will run on other voltages if desired. It is designed be run from a voltage as high as 30 volts if higher voltage high side switching is needed. If the voltage is raised the value of R13 may need to be increased. If raising the voltage causes the voltage regulator, U3 to run warm a resistor can be added at R14 to drop the voltage.
Relay Outputs
Section titled “Relay Outputs”The switch can operate up to 64 independent relays. The relays may be switched on the high side or the low side. Which side is switched is determined at construction time.
The relays are connected to screw terminals although it is also possible to install pluggable block (Phoenix) connectors. Each connector supports eight relays. The connectors also have two pins which are connected to either +V or ground, determined at construction time.
The low side outputs are rated at 50 volts and 350 milliamps maximum. If the relays are supplied from an external voltage source their operating voltage is independent of the power supply voltage.
The high side outputs are rated at 50 volts and 500 milliamps maximum. The supplied voltage is the voltage supplied to the switch minus the drop in the output devices. The input voltage can be increased to accommodate high side switching of 28V relays.
If several relays within a group of eight draw current near the maximum the output device may overheat. In this case it is recommended that such loads be split among several groups. If the loads are high current, power transistors or FETs could be used as current buffers. Relays could also be used as buffers but this adds to the time required to switch the antennas and may preclude using separate transmit and receive antennas.
Amplifier Keying
Section titled “Amplifier Keying”The switch connects to the amplifier keying line of up to six radios. It can be connected in parallel with the amplifiers. It is designed to handle high voltage keying such as is used on the Heathkit SB-220 or Drake L4B.
Radio Inhibits
Section titled “Radio Inhibits”The switch connects to the inhibit inputs of up to six radios. The switch can be set up to pull the inhibit outputs down to inhibit transmission or to pull the outputs down to enable transmission. This can be set per-radio.
The inhibits can be set to only activate when a radio tries to transmit. This allows a relay to be used in the antenna line to connect the radio to a dummy load if it tries to transmit when it is inhibited. It allows the full use of a radio which does not have an inhibit input. There are limits to the configurations where this is useful and where it cannot hot switch the relay.
Some Icom radios which do not have an inhibit capability can be inhibited by the MOAS if it is set to inhibit only during transmit.
If a radio does not have an inhibit input or it cannot be connected to the switch and an outboard relay is not used then the switch will work but some capabilities must not be configured.
Switching Speed
Section titled “Switching Speed”At worst case the time between when an amplifier keying line is opened or closed and when the relay outputs change is less than 200 microseconds. This is insignificant compared to the speed of a mechanical relay.
The switch connects to a computer through a standard USB port. It uses a USB C connector. It does not draw any power from the USB connector. The switch requires an FTDI Virtual Com Port driver. Most versions of Windows will install this automatically. It can also be obtained from www.ftdichip.com. The port number can be viewed and changed using the Windows device manager.
It is possible to configure the switch to connect to a wireless network and perform all the functions identically to the USB connection. You can perform firmware updates remotely.
Ethernet
Section titled “Ethernet”If there is interest in an Ethernet version of the board, I will look to make this available. This version will not have a USB port and will only support WIFI and Ethernet.