Adjusting Modulation Balance. Overview. 2-Level verses 4-Level data. Technical Brief AN142 Rev A0

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Technical Brief AN142 Rev A0 Adjusting Modulation Balance By John Sonnenberg Raveon Technologies Corp Overview The M7 series of radio s from Raveon use a transmit modulation technique called

When Transmitting two-level data, the balance between VCO modulation and TCXO modulation is much less critical.

1 Technical Brief AN142 Rev A0 Adjusting Modulation Balance By John Sonnenberg Raveon Technologies Corp Overview The M7 series of radio s from Raveon use a transmit modulation technique called dual-port modulation. The transmitted signal is applied to both the VCO and to the VCTCXO in the radio s RF synthesizer. The modulation of these two circuits must be exactly the same. When Transmitting two-level data, the balance between VCO modulation and TCXO modulation is much less critical. When transmitting 4-level modulation, the balance between VCO and TCXO modulation must be precise. When sending 4-level data, it is highly recommended that the radio s modulation balance be adjusted on the desired operating frequency, before the radio is installed. Modulation balance tends to change across the radio s frequency band, so it is best to adjust it on the actual operating frequency. Raveon s design has built-in compensation for the balance of the modulation, to keep it relatively consistent across the band. 2-Level verses 4-Level data 2-level data, refers to a signal that digital 1s and 0s are represented by one of two different levels. On an FM radio, such as the Raveon s M7 series, 2-level data is sent as either a positive deviation from center, or a negative deviation. 2-Level Modulation

2 For high-speed data, the digital data is encoded into 4 levels, and sent over-the-air as one of 4 frequency deviations. The 4 different levels correspond to the 4 binary combinations of two bits (00, 01, 11, and 10). 4-Level Modulation It is obvious looking at the two pictures, that the difference between signals on a 2- level signal is much greater that the distance between levels with a 4-level signal. This is why 2-leve radio system have much better communication range than 4-level systems, although their data rate is ½. Modulation Balance Because of the dual-port modulation method used in the M7, there is an adjustment in the M7 that effects the fidelity of the modulation. This is called the Mod Balance setting, and it is stored in register R9 of the radio. If Mod Balance is too low, the rise-time of the leading edge of the signals is too slow. If Mod Balance is too high, then the waveform will overshoot. Both phenomena will degrade the performance of the radio. Modulation balance is set at the factory, and normally should not be adjusted in the field. Only in the case where the radio is changed from two-level to 4-level modulation, or if it is a 4-level radio is changed in operating frequency, should the balance be adjusted. Mod Balance must only be adjusted by trained technicians with appropriate RF communication test equipment.

Proper Balance The following screen captures illustrate properly

Well-balance 2-level signal Well-balance 4-level signal These

into an RF service monitor, and then viewing the recovered FM signal

To properly view this, it is vital that the FM service monitor, FM

Improper Balance The following screen captures illustrate what an

3 Proper Balance The following screen captures illustrate properly balance 2 and 4-level waveforms. Well-balance 2-level signal Well-balance 4-level signal These waveforms are created by causing the M7 to transmit a test pattern into an RF service monitor, and then viewing the recovered FM signal on an oscilloscope. To properly view this, it is vital that the FM service monitor, FM demodulator, and oscilloscope be DC coupled. Improper Balance The following screen captures illustrate what an improperly balance M7 will look like when viewing the recovered FM signal. Over-balance 4-level signal Under-balance 4-level signal Over-balance 2-level signal Under-balance 2-level signal

4 Test Equipment An Agilent HP8910 or HP8921 is the ideal service monitor for testing FM deviation, and looking at the Modulation Balance. The M7 modulation is FM, so a high-quality FM modulation analyzer, FM deviation meter, or FM service monitor is required. Whatever FM deviation monitor is used, it must meet as a minimum these specifications: RF Frequency: Audio Frequency: De-emphasis: Residual FM/noise: 500MHz DC to 10KHz None <50Hz An instrument with AC coupled audio cannot be used to adjust Modulation Balance. Only DC coupled instruments. It is easy to test if it is DC coupled. Simply change the frequency of the M7 by 1000Hz, and the audio output of the FM modulation analyzer should shift in DC voltage. Connect the audio-output of the FM modulation analyzer to an oscilloscope, preferably an old phosphor type, or a DSO will persistence. The oscilloscope must he DC coupled also. Setting the Balance This procedure is only to be used when adjusting the modulation for optimal performance on one specific frequency. After doing this procedure, the factory Modulation Balance settings are modified, and the radio should only be used on the one frequency it was compensated for. Setting the balance is done in the Configuration mode. See the user manual on how to enter the configuration mode. (+++ from a terminal) The balance setting is stored in register R9. Always record its setting before you begin balancing, so that you can revert back to the original setting if needed. Raveon calibrates the M7 s balance in the middle of the frequency band, using the R9 register. For the RV-M7-UC, the middle of the band is 460MHz. There are three test-patterns available to the technician to generate signals that are easy to see on an oscilloscope. The three test signals are generated with the following commands: ATTD 1 ATTD 3 ATTD 8 (send random data) (send pattern at ¼ the baud rate) (send pattern at the baud rate) You may want to turn the RF power down before adjusting the Modulation Balance. RF power may be set to 5 (ATPO 5), to reduce heat during this procedure. Remember after adjusting modulation, set the ATPO back to the setting as it was before turning it down.

Begin by transmitting the ATTD 3 pattern, and adjusting ATR9 for best balance. Once a properly balanced 2-level signal is achieved, verify it by sending random data with the ATDT 1 command.

5 Begin by transmitting the ATTD 3 pattern, and adjusting ATR9 for best balance. Once a properly balanced 2-level signal is achieved, verify it by sending random data with the ATDT 1 command. For M7 radios that use 4-level modulation, verify that the eye opening is wide open. The ATR9 setting will adjust this, and while sending random data, adjust ATR9 for best eye opening. The oscilloscope must be adjusted to trigger at the 50% point in the wavefom to get a good view of the eye opening. Raveon Technologies Corporation 2780 La Mirada Drive, C Vista, CA sales@raveontech.com

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Technical Brief AN139 Rev C22 2320 cousteau court 1-760-444-5995 sales@raveon.com www.raveon.com RV-M7 GX with TDMA Data By John Sonnenberg Raveon Technologies Corporation Overview The RV-M7 GX radio modem