![[SLAC Controls Department]](/grp/cd/soft/images/logo_cd.gif){kind=logo}
![[SLAC Home Page]](/grp/cd/soft/images/logo_slac.gif){kind=logo}
57.1 GENERAL DESCRIPTION . . . . . . . . . . . . . . 57-1
57.2 SPECIFICATIONS . . . . . . . . . . . . . . . . . 57-1
57.3 CONSTRUCTION . . . . . . . . . . . . . . . . . . 57-2
57.3.1 Double-Width CAMAC Module . . . . . . . . . . 57-2
57.3.2 Front Panel with the following items: . . . . 57-2
57.4 CAMAC COMMANDS . . . . . . . . . . . . . . . . . 57-2
57.5 SUPPLIER . . . . . . . . . . . . . . . . . . . . 57-3
57.6 DRAWING PACKAGE NUMBER . . . . . . . . . . . . . 57-3
57.7 RESPONSIBLE ENGINEER . . . . . . . . . . . . . . 57-3 CHAPTER 57 VIDEO CABLE ACCESS MODULE (VCAM)
57.1 GENERAL DESCRIPTION The VCAM module is designed to allow composite video signals to be fed into the CATV cable. It consists of a video multiplexor, allowing one out of eight input signals to be chosen, and a frequency-agile modem which allows the chosen signal to be inserted in a channel in the range T7 to T11 (Carrier frequencies between 7 and 31 MHz.) After up-conversion at the head-end, the signals lie in the range 168 to 192 MHz., in the VHF TV band, and so can be received on a "cable-ready" TV receiver connected to a tap, or by a normal TV receiver which is preceded by a block converter. The module has provision for a single audio input, but this is not used in the SLC application.
57.2 SPECIFICATIONS o Modulator R.F. carrier frequencies are T7 to T11 (7 MHz to 31 MHz). o Input levels should be video standard (1 volt, peak-to-peak) o The output level is +54 dBmv +0 -20, on a type F connector. o A CT126A SAW filter is provided to enable adjacent channel operation. o Video multiplexing is provided so that the module will select one of eight video inputs. Each video channel has a BNC connector and level adjustments. o Two front panel indicators allow the modulation to be set (over/ under modulation). o An audio modulator is provided with a single channel, not multiplexed. Input is from either of two jack sockets, one for 600 ohms balanced and the other for high-impedance input.
VIDEO CABLE ACCESS MODULE (VCAM) Page 57-2 Adjustment for the input level is provided. Standard input level is 0 dBmv. The carrier is enabled/disabled by an internal switch.57.3 CONSTRUCTION
57.3.1 Double-Width CAMAC Module
57.3.2 Front Panel with the following items: o 8 BNC for the video inputs o 1 F connector for RF output to the cable tap o 2 jack connectors for audio input - one for 600 ohm balanced - one for high impedance. o 3 LEDs indicating - overmodulation - undermodulation - absence of video o 8 screwdriver adjustments for input modulation levels o 1 screwdriver adjustment for RF output level o 1 screwdriver adjustment for audio input level
57.4 CAMAC COMMANDS o F16 A0 Write 8 bits to register. W1, W2, W3, select input channel Channel W3 W2 W1 ------- ---------- 1 0 0 0 2 0 0 1 3 0 1 0 4 0 1 1 5 1 0 0 6 1 0 1 7 1 1 0 8 1 1 1
VIDEO CABLE ACCESS MODULE (VCAM) Page 57-3 W4, W5, W6, select output channel CHANNEL W6 W5 W4 ------- ---------- T07 ( 7 MHz) 0 0 1 T08 (13 MHz) 0 1 0 T09 (19 MHz) 0 1 1 T10 (25 MHz) 1 0 0 T11 (31 MHz) 1 0 1 NOTE - The VCAM is not used on Channel T10 at the SLC. - with W4, W5, & W6 all set to zero, the module goes into a pathological state! - Camac address is higher of two slots used W7, Transmitter enable. 1 - enable 0 - disable W8, Local/remote 1 - CAMAC control 0 - channels set by internal DIP switch WARNING - DIP switch numbers do not correspond with bit numbers above. - Bit 5 on DIP switch sets audio carrier on or off. Not available through CAMAC. o F0 A0 Reads register - bit significance as for write. o X = Q = 1 for valid commands. o Z or C Disable transmitter (<1 second) NOTE - If the module is read immediately after a Z, the result will be R1 through R7 set, R8 clear.57.5 SUPPLIER Coherent Systems Inc. Model No. TX 76021.
57.6 DRAWING PACKAGE NUMBER 120-025
57.7 RESPONSIBLE ENGINEER W. Struven