Motorola GI/ Jerrold ADU-445.25 (Motorola Automatic Drive Unit)
New old stock. Boxes may be dirty from storage.
automatic gain control (AGC) devices. Cable system signal levels vary as cable attenuation and hybrid output vary over temperature. The function of the ADU is to monitor the output level of a selected pilot signal at the output of the host amplifier, and send any detected changes in amplitude back to the Bode equalizer. The Bode then makes appropriate corrections in order to adjust the gain of the amplifier to maintain a constant output level for a range of input levels. The ADU/QADU is a plug-in accessory that may be configured into the amplifier (depending on model), or ordered as a separate item for field installation. Use of the ADU/QADU does not reduce station gain. The current ADUs and QADUs use surface acoustic wave (SAW) filters to select the pilot frequency. There are several frequency values available. For the traditional analog ADUs, the pilot frequency is a continuous wave (CW) signal or an available NTSC television signal not scrambled by the sync suppression method. Motorola also offers the QAM ADU, which uses a QAM-modulated digital channel for a pilot signal. This is ideal for cable operators wishing to expand their digital channels below 550 MHz, thereby encroaching into traditional analog space. There is then no need to hold an analog channel. There are two pilot frequency choices available for the QADU, 609 MHz or 711 MHz, both of which are above 550 MHz meaning most cable
operators carry digital channels at these frequencies. The QAM ADU also offers a gain-hold feature. If the pilot level drops by 20 dB or more, the gain is set to mid-range.
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