RV-M7 Data Radio Modem Technical Manual

Tune-up and Alignment

    Do not key the transmitter for more than 30 seconds out of every 150 seconds if the RF power is set above 2 watts.

    Radio calibration and alignment is performed using the ATRx commands.  The M7 modem has been factory calibrated, in should not require any re-calibration when installed, or when changing frequency or channel.  Unless the user is trained in radio test and calibration, the values stored in the R registers should not be modified. 

    Improper adjustment of the radio calibration (R0-R9 and RA registers), can result in failure of the radio modem.  

    Calibration and alignment values are stored internal to the modem in the “R” registers.  (R0-R9 and RA).   For example, to read R5, issue the ATR8 command without any parameter.   To change the setting, issue the ATR8 nn command, where nn is the new value you would like to store.

    Once you read a register using an ATRx command, you may modify its value by entering a “U” for up or a “D” for down.  U or D will change the value by one.  Use this trick carefully, because it modifies the last R register that was read, and it is easy to unintentionally modify the wrong register.

    1. Periodic Calibration

    The only setting that may require adjustment is the center frequency.  After years of operation, all crystals will age and change frequency slightly.  The ATR8 command is used to adjust the center frequency.  Like all narrow-band radios, semi-annual checks and adjustment of frequency is recommended.

    1. Center Frequency
    1. Key the transmitter with CW output using this command: 
      ATTD 7
    2. The modem will now put out CW on the center of the channel.
    3. Read the frequency offset with the ATR8 command.
    4. Adjust the frequency to the center of the channel with the ATR8 command.  You can use the “U” key and the “D” key to change the settings up and down one value in real time. 
    1. TX Deviation
    1. Switch to channel 1.
    2. Key the transmitter into a 50 ohm load using the ATTD 3 command.  The unit will now transmit, and send a digital 0 continuously.  This should be +2.0kHz in frequency for narrow-band radios (12.5kHz spaced channels) and +4.0kHz for wide-band (25kHz channels). 
    3. Adjust the deviation register setting so that the frequency deviation is correct.  The deviation is set with a digital adjustment.   Use the ATR0 command to read or set the deviation level. 
    1. TX Modulation Balance

    (Note: This step is not performed on radios with Radio Type 5)

    1. Set-up a service monitor to monitor the FM deviation of the transmitted signal on an oscilloscope.   The frequency response of the demodulated FM signal must be greater than 10Hz to 5kHz without any de-emphasis.  
    2. Transmit random data with the M7, using the ATDT 1 command.  This command will cause the M7 to automatically key up, and send random data for one minute. 
    3. Verify the DC center of the demodulated data is stable. The random data should be randomly timed 1s and 0s, and have little to no AC component on them. See pictures below for details.
    4. If necessary, change the ATR9 setting so that the long data bit have the same amplitude and DC value as the shorter ones. 
    1. RX Carrier Detect

    The DCD signal from the modem may be generated by detection of RF, using an internal signal called RSSI (Receive Signal Strength Indication).  The RSSI signal is an analog signal representing the strength of the RF carrier.  It is compared with a pre-set value, and if it is above this value, Carrier Detect is asserted.  The pre-set value may be change with the ATRA command. 

    When the modem is used in the Streaming Mode (non-packetized operation, you may wish to configure the modem to require RF carrier detect to be active for the modem to receive data.  Use the ATRF command to enable/disable this feature.

    To set the RF carrier detect level, perform the following steps:

  1. Generate a test signal, 1kHz tone, 1.5kHz deviation, on the receive frequency. Connect the signal generator to the antenna input.  Turn the RF level off.
  2. Watch the RSSI DAC value by issuing the AT$5 command.  The current reading will be sent out the serial port. 
  3. Adjust the RF level to a point where you would like the RSSI to trigger the CD signal. This is factory-set to -110dBm.  
  4. Send the ATRA nnn command.  Set nnn to be equal to the RSSI setting you would like the CD signal to trip at.  The BUSY LED will also indicate an RF carrier when the RF carrier is above the threshold set with the ATRA command.
  5. Generate an RF  signal on-channel with a level of -110dBm.  Verify the Power/BUSY LED stays on. If it does not, repeat step 4, adjusting in increments of 10. 

 


     

     

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