User manual DRAKE DIGITAL TMQAM

[. . . ] This rate must be equal to or greater than the incoming data rate. The output rate will be maintained at the set rate and if the input rate is slower than this rate, the TMQAM and TMQAMasi will add null packets to make up for the slower input rate. The modulators have several test modes that can be selected. In these modes, a pseudo-random binary sequence stream is substituted for the input source. [. . . ] The ENTER button can be used after each parameter adjustment or, if desired, wait until all parameter adjustments are set and then "ENTER" adjustments all at once. The INPUT menu is used to select an inverted clock if this is required. Usually the NORM selection for normal clock will be required. Select INV if an inverted clock is used. The OUTPUT menu is used to select the output mode. The CW setting is for testing and should be selected to allow setting of the upconverter output level using a device such as a signal level meter or spectrum analyzer. For normal operation, one of the MOD settings is required. If the output upconverter uses high side local oscillator injection and inverts the output spectrum of the TMQAM (the Drake DUC upconverters do this), select the MOD-INV setting to provide a normal output from the upconverter. If the upconverter does not invert the spectrum or if you are use the 44 MHz IF output directly, you may need to select the MOD-NORM setting. SETUP PROCEDURES 6 The following chart shows all choices that are available for each parameter. Most CATV systems are using 64QAM or 256QAM for digital video. In the ITU-B mode, the only choices are 64QAM or 256QAM. The ALPHA menu displays the roll-off setting for the baseband filtering. ITU-A is 15% and ITU-B is 18% excess bandwidth. The INTERLV menu allows setting of the interleaver values. The ITU-A setting is fixed at I=12, J=17. The ITU-B mode allows many combinations. The required setting should be specified by the system designer. If the demodulating device must have a particular set of values, then select the appropriate matching setting. For ITU-B, many systems use I128, J4 or I128, J1. The CLOCK menu allows selection of the clock mode of operation. If AUTO is selected, the output baud or symbol rate will automatically track that of the input stream. If FIXED is selected, the output rate will remain fixed at this setting and the TMQAM will add null packets where required if the input rate is slower. If the input rate exceeds the fixed manual setting, an error will result. [. . . ] This warranty shall be construed under the laws of Ohio. The TMQAM and TMQAMasi modulator can operate in either of two clock modes: 1) It can automatically lock to the incoming bit rates producing an output rate determined by the input stream. Power should be supplied by the model PS8 power supply module which also mounts into the DRMM12. 2) It can be set, from front panel controls, to output a desired symbol rate using an internally generated clock. In this mode, when the input bit rate is less than that needed to produce the set output symbol rate, null packets are added by the modulator. [. . . ]