Mocomtech CDM-QX operation manual Config„Ref Reference Oscillator, Config„Mask Mask, External MHz

CDM-Qx Satellite Modem	Revision 5
Front Panel Operation	MN/CDMQx.IOM

5.6.1.7(Config„Ref) - REFERENCE OSCILLATOR

The modem can accept an externally supplied frequency reference, using the BNC connector on the rear panel. However, rather than bypassing the internal reference, and substituting the external signal, the internal reference is used in a low-bandwidth (~ 2Hz) phase-locked loop (PLL), so the modem actually phase locks to the reference external signal. There are two distinct advantages to this scheme:

a.It permits hitless switching between the operation of internal and external reference. There are no sudden discontinuities of frequency and phase in the transmitted carrier.

b.Due to the very low bandwidth of the PLL, it permits the external reference to have an inferior phase noise characteristic than the internal reference of the modem. The narrow loop essentially ‘cleans up’ the external signal. This is particularly important if the modem is being used to supply a 10MHz reference to a BUC or LNB.

Edit the configuration and value of the frequency reference. The value is changed using the STarrow keys. The user should then press ENT. Values of Internal 10 MHz,

External 01 MHz, External 02 MHz, External 05 MHz, External 10 MHz, External 20 MHz, Out Int. 10 MHz, and Auto are possible.

The user should then press ENT. Two examples are shown below:

Frequency Reference:

Internal	10	MHz	(▲ ▼, ENT)
Frequency Reference:			(▲ ▼, ENT)
External	05	MHz

5.6.1.8(Config„Mask) - MASK

Select Transmit, Receive or Reference, using the ◄ ► arrow keys, then press ENT.

Alarm Mask: Transmit Receive

Reference BUC LNB (◄ ►,ENT)

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