Internal Jumper Settings 9
Figure 4 - INTERNAL JUMPER SETTINGS
FRONT PANEL
REAR PANEL
There are a number of internal jumpers that may be
programmed to change certain parameters from the factory
default settings. Some of these jumpers should not be
changed in the field. In most cases, the factory default
settings should prevail.
(1) - CHANNEL PLAN JUMPER - The factory setting for
this configuration is to have no jumper. This provides a
standard EIA CATV plan. If IRC frequencies are required,
add a shorting jumper across the two pins pointed out by
the IRC arrow in Figure 4. For HRC, use the two pins
indicated for HRC. If broadcast frequency assignments are
needed, jumper the two pins indicated by the BCTV arrow.
NOTE: Never install more than one shorting jumper at a
time at this block of headers.
(2) IF LOOP JUMPER - The factory setting is shown in
Figure 4. If this jumper is removed, the 44 MHz IF loop will
be opened and the modulator output will go away. This is
used for special applications and will not normally be
changed.
(3) AUDIO PRE-EMPHASIS JUMPER - This jumper should
normally be in the ON position to enable the 75
µ
Sec audio
pre-emphasis. ON is the correct setting for both the
VM2860 and VM2862 models. If the VM2860 model is
used with an external stereo encoder that provides the
(2) IF LOOP
(5) AUDIO LOOP
(6) VIDEO LED
(7) CLAMP
SLOW
NORM
ON
ON
(8) 4.5 MHz TRAP
(3) AUDIO PRE-EMPHASIS
OFF
OFF
(4) MODEL
SETTING
VM2860
VM2862
(1) CHANNEL PLAN
NO JUMPER = STD
BCTV
HRC
IRC
pre-emphasis, VM2860 pre-emphasis may be defeated by
moving this jumper to OFF. The VM2862 internal stereo
encoder requires this setting to be ON.
(4) MODEL SETTING - This jumper must be set to match
the model number of this modulator.
(5 & 6) AUDIO LOOP and VIDEO LED - These jumpers
must be present in the VM2860. They are not present in
the VM2862.
(7) CLAMP JUMPER - This jumper affects the time
constant of the video clamp. The factory setting is NORM.
(8) 4.5 MHz TRAP - The factory settings are OFF for the
VM2860 and ON for the VM2862. When set to ON, a
4.5 MHz notch filter is inserted in the video input path to
prevent any possible 4.5 MHz energy in the video from
interfering with the stereo or SAP performance. A slight
degradation in video response and LC delay is incurred.
The VM2862 thus requires an ON setting for the jumper.
Mono operation is less critical and the default setting for
the VM2860 is OFF. If audio interference from the video
source is observed on the VM2860, move this jumper to
the ON position. See the Specifications section for details
of the jumper's affect on performance.
