MOAS

My home station is fairly small. There is one tower, a couple tribanders, a forty meter beam, and wires for 80 and 160. As part of being able to operate SO2R from this station I designed and built an automated antenna control system.

Some of the ideas came from things K1GQ had done at his station, but the implementation was my own. There are two boxes - a controller which sits on the table and a switch which is elsewhere. They are connected through a four conductor cable. The controller has knobs and buttons to select antennas and an LCD display which shows which antennas are in use for both stations. The switch has lots of connectors so it can drive the relays in the 2x10 switch, the bandpass filters, and the tribander stack switching.

It has been installed and working for several years now and has all the features I want and is trouble-free.

I did not design this project to be easily duplicated it could be done. The only power tool I used was a drill press. The non-round holes were made with a drill, nibbler, and file. The plastic bezel on the front hides a lot of mistakes.

The firmware is written in assembly language. The development tools are free from Atmel, the company which makes the microprocessors. I can provide the source or object code.

The code is loaded into the controller by connecting it to a PC using a serial connection. The station information - antennas, relays, etc is a simple text file. The program which loads the firmware reads this file and also loads it into the microprocessor.

This is an example of an entry in the file. It is for my 40 meter beam which also works on 30 and general coverage (SWL):

Antenna:2    "40 Beam"
Bands:2      3 4 14
Conflicts:2  2
Relays1:2    7
Relays2:2    15
Alternate:2

Project Documents

MOAS Features

This describes the goals and non-goals for this antenna switch.

MOAS Controller Schematic

This is the schematic of the controller. It isnít very complicated. The bunch of diodes are there to decode the Ten Tec Orion band output, which has ten leads.  The Yaesu and Icom are much simpler. The Elecraft K3 did not exist when I built this controller but it works correctly.

MOAS Controller Parts List

This is the parts list. I believe it is up to date but double-check it against the schematic before ordering lots of stuff.

MOAS Controller Front Panel

This is the template I used to drill the front panel. The parts are in the correct locations, although I ended up rotating the two encoders 90 degrees because it was easier to wire them.

MOAS Controller Rear Panel

This is the template for the rear panel. This shows a DIN connector but I used a microphone connector instead - one hole instead of three. Note that the labeling has stations 1 and 2 reversed - station 2 should be on the left.  Oops.

MOAS Switch Schematic

This is the schematic for the switch portion. I built it in a box and mounted eight DB-25 connectors on it. It connects to the amplifier key line of the transmitters so it knows when a station is transmitting. You will notice that it has the capacity for six transmitters, enough for a modest multi-multi. The controller can only handle two radios, but the switch could be connected to a PC and control a much larger installation.

If I were to do this again I would change the microprocessor to a newer one and use serial shift registers for the high side switching. I have a design for that which I have put on another page.

MOAS Switch Parts List

This is the switch parts list.