CMX264 データシートの表示（PDF） - MX-COM Inc

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CMX264

Frequency Domain Split-Band Scrambler

MX-COM Inc  

Frequency Domain Split-Band Scrambler

8

CMX264 Advance Information

4.1.7 Tx Upperband Output Filter (TXUBOPF)

A lowpass filter whose input is the output signal from the upperband balanced modulator. Its function is to

select that part of the frequency inverted lower sideband which will form the upperband part of the transmitted

scrambled audio. This output is summed with the output of the lowerband Tx channel to form the complete

scrambled signal for transmission.

This filter's response, together with any external filtering e.g. a lowpass filter used to ensure compliance with

statutory transmission requirements, defines the upper frequency of the transmitted scrambled signal.

4.1.8 Tx Summer

This sums the lowerband and upperband to form the complete scrambled audio signal prior to transmission.

4.1.9 Tx Channel De-Emphasis

A de-emphasis circuit at the output of the Tx scramble block. It has a slope of -6dB per octave between

280Hz and 3140Hz. It may be used to compensate for pre-emphasis in the transmission channel.

4.2 Rx Channel

4.2.1 Rx Channel Pre-Emphasis

A pre-emphasis circuit at the input of the Rx descramble block. It has a slope of 6dB per octave between

280Hz and 3140Hz. In descramble mode, it may be selected to pre-emphasize the received audio signal

prior to signal recovery. It may, for example, be used to compensate for de-emphasis in the transmission

channel.

4.2.2 Rx Lowerband Input Filter (RXLBIPF)

A lowpass filter whose function is to select the lowerband part of the received scrambled signal. Its bandwidth

is controlled by the split point setting, which should be chosen to match the spectrum of the received

lowerband.

4.2.3 Rx Lowerband Balanced Modulator

This modulates the output of the preceding Rx Lowerband Input Filter (RXLBIPF). The carrier is identical to

that of the lowerband carrier in the transmitter section. The output consists of two sidebands.

The lower sideband is inverted with respect to the received lowerband, i.e. returned to its original frequency

with respect to the original baseband signal. If the Tx and Rx carriers are the same frequency, the lower

sideband is the desired recovered lowerband.

The upper sideband is not required in the final descrambled output. It is removed by the Rx Lowerband

Output Filter (RXLBOPF)

4.2.4 Rx Lowerband Output Filter (RXLBOPF)

A lowpass filter whose function is to select the lower sideband output of the preceding balanced modulator.

Its output is the lowerband part of the descrambled signal which is summed with the output of the upperband

Rx channel to form the complete descrambled signal.

4.2.5 Rx Upperband Input Filter (RXUBIPF)

A lowpass filter whose cutoff frequency is close to the upper corner frequency of the transmit channel. Its

function is to select the received scrambled signal and reject channel noise at frequencies above this signal.

It is assumed that any transmitted 4kHz SAT tone has been attenuated prior to the Rx channel input of the

CMX264.

4.2.6 Rx Upperband Balanced Modulator

This modulates the output of the preceding Rx Upperband Input Filter (RXUBIPF). The carrier is identical to

that of the upperband carrier in the transmitter section. The output consists of two sidebands.

The lower sideband is inverted with respect to the received lowerband, i.e. non-inverted with respect to the

original baseband signal. If the Tx and Rx carriers are the same frequency, the lower sideband is the desired

recovered upperband.

The upper sideband is a non-inverted, frequency shifted signal and is not required in the final descrambled

output. It is removed by the Rx Upperband Output Filter (RXUBOPF).

2000 MX-COM, Inc.

www.mxcom.com tel: 800 638 5577 336 744 5050 fax: 336 744 5054

Doc. # 20480210.002

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All Trademarks and service marks are held by their respective companies.

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