on the modulation depth selected. While the unit is in USG mode, all other measurement functions are disabled.
Note:
In digital communications, the symbol rate is the gross bit rate, inclusive of channel coding overhead,
divided by the number of bits transmitted in each symbol. Symbol rate is measured in symbols-per-second,
hertz (Hz), or baud (Bd).
In digital television, the symbol rate is calculated as follows;
Symbol rate in symbols per second = (Data rate in bits per second x 204) (188 x bits per symbol)
where;
The 204 is the number of bytes in a packet including the 16 Reed-Solomon error checking and correction bytes
The 188 is the number of data bytes (187 bytes) plus the leading packet sync byte (0x47)
The bits per symbol is the (modulation's power of 2) x (Forward Error Correction). For example in 64-QAM
modulation 64 = 2^6 so the bits per symbol is 6. The Forward Error Correction (FEC) is usually expressed as a
fraction, i.e., 1/2, 3/4, etc. In the case of 3/4 FEC, for every 3 bits of data, you are sending out 4 bits, one of which is
for error correction.
Once the parameters are properly configured, pressing start automatically generates the signal. To stop the transmit, press the stop
key. The signal is generated on the DOCSIS modem port.
Note:
The USG function is a powerful application to check and validate the reverse path for DOCSIS cable
modem operation. The USG is used in conjunction with the QAM analyzer option available on the CX180
series. Refer to the application diagram below.
CX100/110/120/150/180 series e-Manual D07-00-002 Rev B01
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