An automated station control system must be able to route the station antenna to the selected radio. This is the job of the Radio Antenna Switch Controller (RASC). This controller requires an external antenna switch such as a DX Engineering RR8B-HP to switch the RF circuit.


The schematic of the RASC is shown below. Schematic files can be downloaded here.

Radio Antenna Switch Controller Schematic


The RASC is based on the same control logic that is used in the RJ45 Switch and Antenna Switch Controller. Connector J1 connects to the Antenna Switch Control connector on the HMI via a 10-conductor ribbon cable. This cable supplies the address and control lines to select a relay on the RASC. The ASC uses the same connector on the HMI so if you use both the RASC and ASC you’ll need to use a multi-tap ribbon cable (a cable with three connectors installed on it).

IC1 is a CD4514 4-to-16 decoding IC. It decodes a four-bit address to a single output. The address is applied to DATA_1 through DATA_4 then the STROBE pin is pulled HIGH then back LOW to latch the address. The INHIBIT input is then pulled low to enable the output pins. At this point, the addressed output goes HIGH while the other 15 pins remain LOW. The HIGH output is inverted by one of the ULN2803A Darlington drivers to turn on one of the output relays. The INHIBIT pin remains LOW during normal operation keeping the selected relay energized.

This board can control two 8-port remote antenna switches. TB1 (pins 10 to 3) provides connections for ports 1 to 8 on the first switch and TB2 (pins 10 to 3) provides connections for ports 9 to 16 on the second switch.

Ground is provided on pin 2 of both terminal blocks. Pin 1 of both terminal blocks connects to JP4-2. When this jumper is installed an external voltage can be supplied to pin 1 to power the relays on the remote switch.

There are several strapping options on this board. They will be described next.


Strapping options on this board determine both the power source for the internal 12 volt relays and the output of the controller. Which options you choose are determined by the power supplies you are using and the design of your remote antenna switch.

Option 1 – Internal Power

JP1 is installed and JP2 is open if you want to power the internal relays from the HMI‘s primary power or from external power applied to the ASC. To power the RASC from the HMI, install JP4 on the HMI board to provide power to this board. This source is reverse diode protected current from this board can’t flow back to the HMI board.

NOTE: The HMI can be powered from any voltage from 9 to 72 volts (depending on the DC-DC converter installed) so this option should only be used when powering the HMI from a 12 volt nominal power supply.

Option 2 – External Power

The RASC can be powered from an external +12 VDC power source. To enable this option, remove JP1, install JP2, and install a 2.1mm x 5mm coaxial power jack at J4. You can also power the RASC from an externally mounted power jack by soldering a jumper from pin 1 of J4 to pin 2 or 3 (i.e. make pin 1 of JP2 ground) then connecting the external power jack to JP2 with (-) on pin 1 and (+) on pin 2 of JP2.

NOTE: When using both the RASC and the ASC, you only need to install the coaxial power jack on one of the boards. Set that board for external power (JP2 installed) and both boards for internal power (JP1 installed). Do not install JP4 on the HMI.

Option 3 – Output

The RASC is designed to accommodate different remote antenna switch configurations. Some require (+) voltage on their input to pull in their antenna relays while others require a ground on their input to pull in their antenna relays. Consult your switch’s documentation to determine which method they use.

Source (+12 VDC)

To source a (+12 VDC) voltage to your remote antenna switch, install a jumper between pins 1 and 2 on JP3 and use either the Internal or External Power options above to provide the +12 VDC power. Connect the return (ground) on your remote antenna switch to pin 2 of the terminal block so both systems have a common ground.

Sink (Ground)

To sink the external antenna relay’s inputs to ground, install a jumper between pins 2 and 3 on JP3. Connect the return (ground) on your remote antenna switch to pin 2 of the terminal block so both systems have a common ground.

External Power

Some remote antenna switches may require +12 VDC on a common pin and a ground to be applied on an input to pull in a relay. In this case, install a jumper between pins 1 and 2 on JP3 and a jumper on JP4. In this configuration, +12 VDC will appear on pin 2 of both TB1 and TB2.

Another option is to provide external voltage for the remote antenna switch. This would be desirable if your remote antenna switch requires a voltage other than +12 VDC. To do this, remove all jumpers on JP3 and install a jumper on JP4. Connect the external voltage to pin 2 of TB1 or TB2.

NOTE: If the external voltage is +12 VDC (nominal) you can use it to power the the internal relays on the RASC too. Just install a jumper between pins 1 and 2 on JP3.

Please feel free to contact me if you have questions about configuring the RASC or ASC for your remote antenna switch.

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