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When first setting up if you are not using the full handshaking on the interface, in particular using a 3 wire system (transmit, receive and ground) it is essential to strap DTR high on the 15 way D type connector ( see diagram on 3AS page).

If you are having trouble with the system, leave everything connected but stop transmitting - if you can see the LEDs flashing you have interference!

If you checked points 1 and 2, but the LEDs seem fine. Connect the modems to 2 PCs with the antennas at least 2m apart and at least 1m away from all other electronic equipment, install SATERM and try a test transmission between the PC’s - this will determine whether it is the modems or other equipment that is at fault

Check surrounding environment, radio waves can be affected by, trees, hills or large mounds of earth, a very large quantity of paper (i.e a warehouse full!), a large amount of metal (Faraday cage).

Some buildings have metal within the walls or windows that can be of sufficient quantity to cause problems in this instance mount the antenna on an external wall

If the modem is not provided with sufficient voltage or power it will not perform to specification, resulting in spurious loss of transmission or data corruption. From our experience, industrial vehicle’s are notorious for having unstable power supplies!


If your CD light flashes Amber you probably have interference! Change frequencies.

When you first power up the units without initiating transmission - CTS should be on (Red) and steady, RTS comes from your equipment may be either on (Red) or off. The other LEDs should only light when there is transmission

On the 3AS CD off = no signal, green = incoming signal, red = xmit, amber = foreign signal

Antenna Location

Ideally the antenna should be at least 2 m away from any other antenna or electronic equipment and mounted as high as possible.

If you need to have more than one antenna, mount them one above the other - not on the same plane

When mounting an antenna against a wall or potentially reflective surface, the following formula should be applied to calculate how far away from the wall the antenna should be mounted: 300 divided by the frequency = 1 wave length therefore 458Mhz equals a wavelength 655mm add to this at least half a wave length giving a total of 982.50mm


In order to change the settings - it is better to use the program cable, unless you are familiar with the SL commands or have a unit with an LCD display.

Don’t forget you if you get in a muddle, “return to factory settings” and start again!

Saterm is the most reliable program to use. Always come out of the program properly by typing E to exit


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