|
GBC AVS8 AUDIO/VIDEO SWITCHER
INTRO
Audio is becoming an increasingly important
component in video surveillance, but relatively few multi-camera switching systems
are equipped to handle a second signal path. The GBC AVS8 switcher is one of
the exceptions, we’ve been looking at this compact, easy to use 8-channel audio
video switcher
COPY
Before we go any further let’s get the bad
news out of the way. Final assembly and quality control procedures at GBC appears
to have some serious problems! Our sample AVS8 emitted a high pitched alarm
signal the first time it was switched on. Despite re-initialising the unit
several times the tone persisted. There was clearly a fault so we opened up the
casing, to see if there was anything obvious, that could be put right.
The cause of the fault was immediately
obvious. The wedge-shaped steel console is in two parts, on the bottom panel
there’s a threaded stud set into the panel, for securing the mains earth wire.
The stud is immediately adjacent to a small PCB, for alarm switching functions,
the end of the stud was in contact with one of the tracks on the PCB, causing a
short-circuit. Indeed the thread was so long that it had scratched the surface
of the PCB. Fortunately this occurred on the low voltage DC side of the
circuit, but the stud was only around 1 cm from the mains transformer. The consequences
of such sloppy design are obvious!
Fortunately this was the only serious lapse
in what is otherwise a generally well thought out product, though, as we shall
see in a moment, the case design leaves a lot to be desired. The AVS8 is an 8
channel video and audio switcher, with several unusual features, apart from the
audio switching facility. The first has to be simplicity of use. Instead of using
on-screen displays or additional controls, all programming functions are carried
out using just the 8 selector and two mode buttons, and their associated LED
indicators. It has dual monitor outputs, each of which can be independently
switched. Video switching employs a vertical interval delay, so that there’s
negligible disturbance at the switching point when using phase line-locked
cameras. It has an alarm input interface, associated with each camera input,
that enables a number of programmed responses, and all settings are protected
by a non-volatile memory.
The design is remarkably straightforward. On the
top of the panel there are just ten buttons, each with a red LED indicator. On
the far left is the monitor selector button. Next to that are the 8 camera
selectors, and on the far right is the auto/manual sequence button. On the side
of the console are two presets, one for setting the volume of the internal
speaker, the second for adjusting the audio output level. On the back panel
there are 10 BNC sockets, 8 for the camera inputs, and two for the monitor
outputs. There’s a matching set of audio connections, and three multi-pin
connectors. The 25-pin D connector is for the alarm inputs and outputs. The
other two are marked ‘Auxiliary Connections’, and ‘Slave P1+3’ but no mention
of them could be found in the instruction manual. They are connected to the
main PCB, presumably they’re for future upgrades, but some indication of their
purpose would have been helpful.
Normally we avoid delving too deeply into
case design, except when there’s an obvious flaw, such as the earthing stud
already discussed. However, the case on this product deserves further scrutiny
as important adjustments can only be accessed from inside the box. In order to
change the video connections -- factory set with 75 ohm termination’s -- it is
necessary to open the case and remove resistors, soldered to the PCB. The
manual broadly outlines the procedure, but do not give specific instructions, or
identify the particular components. It does say that that; ‘it should only be
carried out by staff qualified to, or experienced in, modifying mains-powered
equipment’ but that’s not a sufficient warning, and would do little to deter a
rookie installer, determined to ‘have a go’. Removing the case lid is easy
enough, there are only two screws, but separating the two halves is quite
tricky, and putting them back together again, without damaging the PCB, requires
practice.
The external adjustments are a lot easier to
carry out. The dwell time for the sequence can be altered from 2 to 60 seconds,
in 15 steps. To do this the auto button has to be held down, with camera
buttons 1 and 2 increasing or decreasing the dwell time. The approximate setting
is shown by the blink rate of camera 1 and 2 LED indicators. This method is simple
enough, and very economical in the use of controls, but it’s not very precise,
and some trial and error may be needed to get the exact timing. It’s worth
pointing out that this is a global adjustment, and it’s not possible to alter
the dwell times of individual cameras.
Camera inputs can be enabled or disabled
using a similar technique. Holding down the auto button, (in the manual select
mode), illuminates all 8 camera indicators; these can be individually included
or excluded from the sequence by pressing the appropriate camera buttons.
There are various alarm options. Upon receipt
of a trigger the switcher selects the relevant camera input, which can be
routed to monitor output A or A and B. The display will remain on that camera
for a pre-set period, from 4 to 120 seconds, the delay is set in a similar way
to adjusting camera dwell time. After the alarm timer expires the sequence can be
set to return to one of three states: back to auto sequence; remain on the
alarmed camera, providing it was not in audio sequence prior to the alarm
event; or return to the originally selected camera. The alarm interface is
factory-set for normally open contacts, if it is necessary to have NC contacts
then a link has to be soldered onto the back of the D-socket (supplied with the
unit). Switched audio is routed through small built-in monitor loudspeaker,
mounted on the right side of the case, and the audio outputs (one for each
monitor) on the back panel.
All programmed settings can be protected
against accidental or deliberate tampering by a simple security feature.
Holding down the ‘auto’ button at switch on displays the state of the
programmed adjustments, which includes camera dwell and skip, action after
alarm, alarm event display, auto sequence following an alarm and monitor access.
These can be alternately enabled or disabled.
PERFORMANCE
Video signals pass cleanly through the
switcher, with no significant increase in noise, reduction in stability,
bandwidth or colour fidelity. Camera switching is fast and on-screen disturbance
at the switching points is minimal, even on non line-locked sources.
Needless to say audio quality from the 40mm on-board
speaker is not that wonderful, though in most installations the output will
normally be routed through to the video monitor.
CONCLUSION
The design of the case, and in particular the
short-circuiting earthing stud is a cause for concern. We’re also unhappy about
the method used to change video termination’s, some form of external switching
would be preferable, and far more flexible, to removing resistors on a PCB
panel.
Operationally, however, the AVS8 works well,
the video and audio circuitry is largely transparent to the input signals, and
the clever utilisation of the front panel controls contributes to ease of use.
PRODUCT SPECIFICATION
Video inputs 8 x 1v p-p CCIR/PAL composite,
terminated 75 ohms
Video outputs 2 x 1v p-p CCIR/PAL composite, terminated 75 ohms
Video bandwidth more than 6Mz
Video crosstalk less than -48dB
Sequence timing 2-60 seconds in 15 steps (2/3/4/5/6/8/10/12/15/20/25/30/40/50/60
seconds)
Alarm timer 4-120 seconds in 15 steps (4/6/8/10/12/16/20/24/30/40/50/60/80/100/120
seconds)
Alarm inputs 8 x N/O, via 25-pin D-Sub connector
Alarm output N/O for VCR triggering (rated 28V DC
0.5A max)
Audio inputs 1v p-p 600 ohms
Audio bandwidth 100Hz to 10kHz
Power supply 230 VAC 50Hz
Weight 0.7kg
Dimensions 153 x 62 x 284mm
PSI RATINGS
GBC AVS8
Product 7
Product design 5
Build quality 5
Ruggedness 7
Operation 7
General functions 7
CCTV functions 8
Ease of use 8
Instructions 6
Manuf. support ?
Performance
Video quality 9
Switching 9
Audio 8
---end---
Ó R. Maybury 1996 2511
| 
