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"Test Chest" is a deceptively powerful Product, so lets spend a few moments together getting to know it, and exploring it's features. In fact, most of the major features are immediately obvious as they are menu selected, but other more subtle features may be a key press or two away.

MOST functions are menu selected from the page presented after the Test Chest initially powers up (initiated by pressing the "Pwr" key of the lower key cluster) and by using the navigation keys and the centre "Select" key of the upper switch cluster. In a number of instances, Test Signal Generation and the Wave-Form display mode for example, selection of the required output Test Signal or WFM display mode, will require selection via a sub-menu.

Users should be aware that some Menu options, although subtle, will alter the mode of operation substantially. Turning off an unused SDI output to save power, for example when using the CVBS output, is a menu option; howeverthe functions actually enabled are clearly shown on the Menu page.

Which-Wire?    A powerful investigative mode in which Test Chest emulates the original Murraypro    Which-Wire? Unit, automatically awakening from slumber as soon as a signal is applied to the input BNC, and it is not necessary to manually power the Test Chest up in this mode.

Which-Wire? then not only automatically displays the TV signal present on the input BNC via the internal 16:9 LCD screen, but additionally identifies between 525/625 & SDI/CVBS signal types, by means of an on-screen banner.

Users should connect to the lowest BNC connector, designated "WW?" at the bottom right of the front panel, and be aware that this connector always correctly terminates an input with 75 ohms. A fundamental feature of the Which-Wire? mode is that both Analogue and SDI signals enter the Unit via the same connector, so it will never necessary to double guess what signal type may be present on a given cable as the Test Chest will auto-switch between SDI and CVBS inputs.

This is an important and vital difference between the Test Chest and some other products, which will require the User to consecutively offer the unknown signal to both of the separate SDI and CVBS inputs, in turn.

TSG. The Test Chest contains a very powerful, high quality Test Signal Generator that is eminently suitable for testing external equipment. Menu selection of the 15 different Test signals is easy, and the Generator can provide simultaneous SDI and CVBS output streams of the selected Test Signal. To increase battery endurance, the SDI OP may be disabled via the menu, reducing the power drain if only a CVBS OP is required.

It is possible to insert a local identification text string in to the output video, a particularly useful feature when feeding long lines. To conserve battery power the LCD panel may be turned off via the lower switch cluster, reducing the load substantially, once the TSG has been set up.

An audio oscillator with balanced OP is incorporated, providing a useful source of spot frequency audio for generic testing. This is described in more detail later.

Measurement.    Test Chest incorporates an internal TV Wave-Form Monitor function. TV signals may be displayed from either SDI or CVBS sources as either standard video signals, or in Parade mode (SDI only) where the colour information is sequentially switched between either the RGB or YUV channels.

Embedded audio level for any channel pair 1&2 through to 15&16 may be displayed on the LCD panel, whilst an indication of Stereo phase is also given. A Parade mode is available with SDI signals. The signal may be displayed in one of 3 menu selectable Parade modes: YUV, RGS or YRGB. To ease channel identification, the LCD display adopts the colour of the signal being instantaneously presented.

If desired, the CVBS and/or SDI OP of the Test Chest may be fed on to an external picture monitor in the event that a larger display is required. In the Composite video display mode, the HF response extends up to about
10MHz.

Test Chest provides a very useful high impedance feature that enables simple investigative maintenance procedures to be undertaken without loading the external circuitry significantly.

The second BNC up from the bottom on the right hand side is specially buffered and presents a 1 Megohm // 20pF input impedance, suitable for use with a conventional oscilloscope probe.

To maximise flexibility at remote locations, Murraypro include a switchable x1 & x10 probe with the Test Chest when the optional ever-ready "Pouch style" case is ordered. The HF response extends above 10MHz, so the 'scope function can provide a useful general maintenance tool, when more powerful oscilloscopes are not available. Menu selectable gain settings of 200, 100 & 50mV/div are available.

Although the internal audio amplifier is operational in WFM mode, it becomes a really useful high impedance tool foraudio investigation, when coupled through the high impedance port. Audio volume level is controlled by the "up"and "down" menu secection.

Using the Test Chest's 75 ohm WW? input port, set initially to WFM or LCD Monitor mode, Test Chest provides accurate audio level monitoring of embedded audio signals, via the sub-menu's "Audio" options. Audio levels are presented as numeric values in tabular form on the LCD screen. By eliminating bargraphs for level indication, it is immediately possible to unambiguously differentiate between an AES reference level at -20FS and an EBU reference at -18FS for example, with a high degree of accuracy, in fact to a fraction of a dB.

Using the Audio sub-menu, selection between A1 & A2 or A3 & A4 pairs are possible for each of the 4 audio groups.
Additionally, the internal Loud Speaker Amplifier may be menu selected between the Left or Right channel of any stereo pair.

Stereo phasing is indicated by the dynamic ratio of:
"Sum" to "Difference",     also known as       "Mix" to "Separation".

"L + R" = Sum (Mix)    "L - R" =   Difference (Separation)
M = 100%, S = 0%     would indicate two signals perfectly in phase,   whilst    
S = 100%, M = 0%     signifies stereo disaster, with a total inversion of one channel.

Test Chest offers a Time Domain Reflectrometry mode for the identification of cable problems. The system launches a pulse into the end of the problem cable, which is connected to the WW? BNC port.

With a correctly terminated cable, all the launch energy is absorbed by the terminating load at the far end of the cable; however should the load not correctly match the cable's iterative impedance, a percentage of the launch energy will be reflected back from the far end of the cable. It is this reflected energy which Test Chest detects and displays on the LCD's display.

The X axis (Time-Base) of the display is calibrated in Metres, with an unterminated cable showing a positive reflection, and a short circuit as a negative reflection at the indicated distance of the analomoly.

On a 75 ohm system, Test Chest is easily able to differentiate between a correctly terminated system and one which is:-
a) Open circuit (unterminated).
b) Incorrectly terminated in 110 ohms.
c) Incorrectly terminated in 50 ohms.
d) Double terminated with 2 separate 75 ohm loads.
e) Correctly terminated, but with an unterminated "stub".

Unless significant, mechanical damage or cable crushing is unlikely to be detectable.

Test Chest offers, via the menu's audio sub-page, an audio oscillator generating tone, available as either an analogue source, or as a 48KHz AES encoded stream.

Selection between the low impedance balanced baseband audio, or the 110 ohm AES bitstream, is made by the miniature toggle switch which is mounted in the centre of the left end-plate.

Oscillator spot frequency, 100Hz, 400Hz, 1 KHz & 10KHz, is set via the audio sub-menu.
Amplitude 0dBU, +2dBU & +4dBU is also set via the audio sub-menu.

Output loading: Test Chest follows current audio practice with a low output impedance, and does not anticipate a 600ohm load. Loading the XLR3-M balanced output with 600 ohms will cause the amplitude to drop by-0.3dB nominally.