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Improving Streaming Mode Communication Range

For most applications, Raveon suggests operating the M7 VHF/UHF data radio modems in the “Packet Mode”.  In packet Mode, the radios verify the data is error-free using a 16-bit CRC.  They can be over-the-air Pinged.  The packets IDs and can be repeated.   But, in certain circumstances, such as when low-latency is required between transmit data and receive data, the streaming mode in the M7 data radios can be enabled.

In streaming mode, there are many configuration options that will affect the performance of the system.  Following is a list of some things to consider when using Streaming Mode in the radio modem.

  1. In streaming mode, the M7 data radio modems will very often output an extra few byte of random data noise at the end of a packet. The weaker the signal, the more likely the extra noise bytes are appended.
  2. On a polled radio system, consider the time-out-delays carefully. To account for serial port delay, T/R turn around, and a few noise bytes you may want to add a little extra to the time-out.
  3. As always, use the best antennas possible, and get them as high as practical. This may be a huge improvement to the link margin.
  4. Make sure all the antennas physically tuned to the right frequency.
  5. The DC power supplies must be electrically clean and able to supply enough power?  12V at32 amps is the minimum, we recommend 60 watt power cubes.
  6. To help measure link-margin, the ATRS command tells you the signal strength in dBm of the last packet received.
  7. To improve reception reliability with weak signals, configure the data radio modems to send longer pre-amble patterns.  If you have them send a 1-3 extra bytes of preamble, it will increase the reliability of the link, especially in the fringe areas.  ATR5 command sets the number of bytes of preamble transmitted before each transmission.  Normally they are set to 5 bytes, and you could try 7 or 8 and see if it helps.
  8. Some systems will work better if the Carrier Detect signal is used in streaming mode.  If ATRF is set to 1, then the modem will only try to decode over-the-air messages if the RF signal strength is above a fixed level set by ATCD.  When you have good link-margin (strong signals) this works great, and will allow a streaming mode radio to pick-up 100/100 messages.
    But… if the signal is weak, or below the carrier detect threshold, then it makes the modem miss data that it could have decoded because the modem is capable of demodulating data over-the—air on very weak signals.

Filed under: Programming and Configuring, System Design | Posted on August 31st, 2013 by John Sonnenberg

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