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FCS Software

FCS User Guide

Free Channel Scan (FCS) is designed for one-way transmission between one transmitter and one or more receivers when there are at least two different transmission frequencies available. The transmitter monitors the noise level of the channels between the transmissions and finds the best transmission channel. Software supports maximum of 16 channels. This feature is beneficial especially when license free channels are used and there could be other transmitters using the same channels.

For older SATELLINE 3AS and Epic radio modems without E2 marking , the Free Channel Scan function requires the loading of the special FCS Modem Software. Required software is Satelline_3AS_and_Epic_FCS_sw_0_93.sff or greater) to SATELLINE-3AS/(d) radio modem. Compared to the standard software of the SATELLINE-3AS/(d), this software does not have the Message Routing functions and repeater functionality is neither supported when FCS is activated.

For new SATELLINE 3AS and Epic radio modems with E2 marking, Software version 3.07 or greater is required. This adds support FCS, and no special software is needed. When FCS is activated Message Routing and repeater functionality cannot activated.

To make the usage easier there is a FCS terminal software program for persons with access to a PC. With this program it is easy to configure the modems to use the FCS function. The FCS Terminal Software reserves the data port of the radio modem so it is not possible to transmit user data at the same time.


Below is a quick note to describe the mechanism and time to switch channels the process and roughly how it works 

  • Each transmission from the master is prefixed by a short data packet containing reference information for the slaves. This is called a Beacon”
  • The parameter “Beacon Interval” is used by the master to transmit additional Beacons when the gap since the last user transmission exceeds this time interval.
  • The recommended minimum setting for Beacon Interval” is 250ms.
  • In between user data and beacon transmissions the master transmitter monitors all the channels listed within its internal FCS table (which is soft programmable)
  • When the Master detects foreign transmissions on the current channel (exceeding a programmable threshold) it will initiate a change of channel
  • First the Master sends a beacon containing the instruction to change channel, and then it switches all subsequent transmissions to this channel
  • If the Slaves receive this change channel” beacon they will automatically and immediately switch to the new channel.
  • If a Slave loses communication with the Master I.e. it doesn’t see a beacon for a period in excess of the “RX listening time” parameter it will initiate a search
  • A search consists of stepping through the channels within the FCS table (which should be set the same in all Salves as well as the Master)
  • Each channel will be monitored for the RX listening time” trying to detect a beacon. If one is not detected we switch to the next channel
  • Thus the maximum time to complete a full search is the RX listening time” multiplied by the number of channels
  • The recommended setting for RX listening time” is at least twice the “Beacon Interval”.
  • This ensures that the receiver should see at least one Beacon when it scans the correct channel.
  • The FCS table supports a maximum of 16 channels - There are 15 usable licence exempt 25kHz channels in the UK
  • Using the minimum recommended RX listening time” (500ms) it will take approximately 8 seconds to scan 15 channels.
  • Assuming clear communications on the new channel, this is the maximum time it will take a receiver to switch over
  • Statistically the average time to search and find the new channel will be half this figure
  • In practice the receivers tend to see the change channel” beacon so there is no loss of data

UK Frequency list (25Khz channel separation) If you are in the UK and are looking to save some time, you can cheat and cut & paste the list below!