Murraypro
Test Chest 3G
FAQ & User Notes
Iss:3 September 2011
Frequently Asked Questions:-
General Issues.
The Test Chest 3G is shipped with a partially charged Lithium Polymer Battery, and Murraypro recommend that your new Unit is given an initial charge prior to use. Therafter, you may expect the charge period to be around 2 hours for a discharged battery.
Q: Is the Test Chest 3G waterproof?
Q: Can I damage the LCD's touch screen?
Q: Is the Test Chest vulnerable to viruses such as the Stuxnet?
Q: What is the secret of the Test Chest 3G's amazing speed of operation?
Power Issues.
Q: Can I use the Test Chest 3G under external mains power whilst the battery is being charged?
Q: The Test Chest 3G appears to have no power switch, so how do I switch it on?
Q: How do I get the Test Chest 3G to stay switched on?
Q: Will I damage the battery if the Test Chest 3G battery runs 'flat'?
Q: Can I store the Test Chest 3G with a 'flat' battery?
Generation.
Q: How do I set TC3G to operate on a particular Video Standard?
Q: How do I select the required Video Test Signal?
Q: How do I configure the Audio?
Q: How do I set which Group the embedded Audio is inserted on?
Q: Can you explain, what is, and how to use, "Clapper Board"?
Q: I've set up the Generator as I want it, but there appears to be no_Output?
Q: Just how good are the output signals?
Q: Just how 'fine' are the Horizontal and Vertical lines on the Grill pattern?
Monitoring.
Q: I have heard a lot about your Murraypro “Which-Wire?”, what is it?
Q: OK, sounds great! So how do I initiate, and use, this “Which-Wire?” Mode?
Q: If I leave the Test Chest monitoring in “WW?” mode, will it detect a change of input?
Q: Termination of video lines is always important, do I need to terminate the “WW?” input?
Q: Does the Test Chest 3G have any “unterminated video inputs?
Q: How do I use the Oscilloscope mode?
Q: Can I use the Oscilloscope as an 'Audio Signal Tracer'?
Q: How do I mute the front speakers, when I am using the external headphone socket?
Q: How do I use the TDR/Cable Test?
Q: How can I use the TDR on long cables?
Q: How do I monitor an AES input'?
Q: How can I accurately match an XLR's 'Balanced 110 ohm AES input' to BNC #3's 75 ohm Port?
Q:Do the Balanced Audio inputs and outputs terminate in 600 ohms?
Q: Why doesn't Test Chest 3G offer an “Eye” display?
Q: Can I use the Test Chest 3G to show proximity to the 'Digital Cliff'?
Q: Do you have a list of the TV Standards covered?
Do you have a list of the Signals Test Chest 3G can generate?
General Issues.
Q: Is the Test Chest 3G waterproof?
A: NO. Whilst we have attempted to protect the Unit from day to day hazards such as shock, dust and an occasional moisture drip, the Unit is not sealed and operation in wet/damp conditions, or a determined attack by coffee or tea, are not permissible. Consequently damage caused by such activities would not be covered by Warranty.
Q: Can I damage the LCD's touch screen?
A: YES. Damage is possible, so use ONLY a 'soft touch' on the touch screen, please. Use of any sort of stylus or probe is strongly discouraged by the Manufacturer of the 'touch screen'. Damage to the panel's front surface, caused by inappropriate operation of this type, is specifically excluded from Warranty cover. Use of a screw driver, or any ball point pen, is highly likely to cause rapid and permanent damage to the front surface.
Q: Is the Test Chest vulnerable to viruses such as the Stuxnet?
A: No, certainly not. The Test Chest 3G uses FPGA logic that is configured from high speed look up tables, not by an on-board computer that can be accessed via a USB (or similar) Port. This not only eliminates the possibility of external contamination via a User access port, but vastly speeds internal configuration, making the Test Chest 3G impressively fast to operate.
Q: What is the secret of the Test Chest 3G's amazing speed of operation?
A: Intuitive Touch screen configuration eliminates 'configurable keys', and subsequently high speed lookup tables blast configuration data into the FPGA without the requirement for a “PC type” interface, and it's inevitable turgid response.
When the legend changes on the bar at the top of the picture....that's it, the TC3G mode HAS changed, and normally this response is essentially instantaneous!
Power Issues.
The Test Chest 3G is shipped with a partially charged Lithium PolymerBattery, and Murraypro recommend that the Unit is given an initial charge prior to use. You may expect the charge period to be up to 2 hours or so for a discharged battery; and perhaps a little longer when 'running in' a new battery pack.
Q: Can I use the Test Chest 3G under external mains power whilst the battery is being charged?
A: Yes. Using the supplied PSU, Test Chest 3G may be used indefinitely under external mains power and without regard to battery charge condition. Intelligent battery charging and sophisticated power management ensure that the Battery can not be over-charged, even if external dc power is left permanently connected. Battery over-voltage/current and deep discharge protection are provided, whilst an on-screen bar icon provides an indication of remaining battery capacity.
Q: The Test Chest 3G appears to have no power switch, so how do I switch it on?
A: The Unit is controlled via the touch screen interface. Awakening upon just a single touch, the LCD displays a green icon in the bottom-right of the LCD panel. This green circle must be touched within 4 seconds of it's initial appearance to confirm the validity of the 'Wake Up' command; if not, the Test Chest will automatically resume it's hibernation mode and power-down to preserve battery power. This double selection requirement confirms that the power-up request was valid, and not the consequence of a 'nuisance' contact with the LCD panel. This feature is particularly valuable in preventing accidental discharge whilst in storage.
Q: How do I get the Test Chest 3G to stay switched on?
A: There are a number of separate, and different, power-down conditions to consider:-
The Test Chest 3G is in “Which-Wire?” mode (read more on this below), and the input video signal has been removed. A moment or two after the removal of the input video, TC3G will automatically resume hibernation mode, ready for it's next mystery video stimulus. This automatic power-on and power-off feature is one of the major features of our Murraypro “Which-Wire?” logic.
Approximately 10 minutes after the last touch-screen command, the Test Chest 3G Unit will power-down automatically as a battery power conservation measure. This automatic shut down may be over-ridden by selecting “Manual”, rather than “Auto” on the main Menu's power option. Be aware however, that you will now need to manually select “OFF” on the main Menu at the completion of a period of operation or the Test Chest 3G will continue to operate until the battery has completely discharged! (Take care to ensure that you do not store the Test Chest 3G with it's battery in a discharged state, as this will seriously jeopardise the battery life.)
During battery powered operation the battery voltage is continuously monitored, and when the low voltage cut-off point is reached Test Chest 3G will shut down automatically, preventing deep discharge of the battery. Prior to this cut off point, the on-screen 'battery bar' icon will have been warning of impending cut off.
Q: Will I damage the battery if the Test Chest 3G battery runs 'flat'?
A: NO, there is low voltage cut off protection to protect the battery from 'deep discharge', but read on about storage.
Q: Can I store the Test Chest 3G with a 'flat' battery?
A: NO, this would be most unwise, and will adversely affect subsequent battery life. A discharged Lithium Polymer battery should always be recharged as soon as practical. Remember that the Test Chest's intelligent battery charger circuitry will prevent overcharging, and low voltage power could be left permanently connected.
Generation.
Q: How do I set TC3G to operate on a particular video standard?
A: This is always at least a 2 command sequence, and one which may extend to several more menu selections. The current selection will always be displayed on the banner at the top of the LCD panel, and guided by this, progress through the set up process is highly intuitive.
On the main menu select, with a single tap, one from the following.... 'SD/HD/720/3G' as appropriate. This defines the Standard Group.
On the main menu select 'Standard'. Multiple screen-taps will toggle Generation through the available options.
If appropriate to the chosen Standard, toggle through 'Interlace' or 'Progressive'.
If appropriate to the chosen Standard, toggle through 1.000 or 1.001 as required.
Confirm that the Banner display matches your requirements.
During our Test Chest 3G demonstrations, we always emphasise the impressively short reaction time between the intuitive touch-screen's command entry, and the execution of an instruction. When the legend changes on the bar at the top of the picture....that's it, the TC3G mode really HAS changed!
Q: How do I select the required video test signal?
A: Using the main menu navigate to, and select, the Colour Bar icon. Select the required waveform from the available options. You may subsequently wish to return to the main menu page to continue with other selections......
Q: How do I configure the audio?
A: Using the main menu, navigate to the 'Generate Audio' option. There are 3 options for the 'Source' of the Audio.
Internal Oscillator, which can be menu configured for Frequency and Amplitude. This generates a common signal that may be enabled (or not) on Channels 1, 2, 3, 4, independently.
AES: Unbalanced AES presented to BNC #3 will be processed and available for insertion as a stereo audio source. There is no facility for adjusting this level, which is set for 'Unity' dBFS-in/dBFS-out; ie -18dBFS-in = -18dBFS-out.
Balanced Analogue audio that is available externally as a stereo source is presented to the D-25 connector; most probably via the Audio POD's XLR3-F connectors, as this is usually highly convenient. Users may of course wish to construct their own D-25M to XLR3s, or custom pin multi-way connector, to interface with their own equipment if this if felt to be more convenient, or practical. There is no facility for adjusting level, which is 'Unity' dBU-in/dBFS-out; ie 0dBU-in = -18dBFS-out, ie matches EBU Scaling.
Q: How do I set which group the embedded Audio is inserted on?
A: On the Audio sub-menu select 'Group', and toggle through to the required Group, which will be displayed on the Banner at the top of the LCD.
Q: How can I tell if an AES input signal is synchronous with Video Clock, and consequently suitable for inserting on to the Test Chest 3G's audio output?
A: Select the Audio Monitor page via the Home Menu; apply the 'Video Reference' signal to BNC1 and the unbalanced AES input signal to BNC3 (remembering that the Utility AES Transformer will convert between Balanced and Unbalanced AES signals iif required). The difference in frequency (if any) between the AES 48KHz Word Clock & TV Vertical Clock will be presented on a flashing icon at the difference frequency. A 1Hz 'Beat' rate indicates an error of approximately 20ppm.
Of course, this Utility may be used to check whether ANY particular AES input applied via BNC3, is synchronous with the Reference input that you apply via BNC1.
Q: I've been told that the Test Chest 3G really can operate on two different TV Standards simultaneously; can this be true?
A: Yes, most certainly; simultaneous Dual-Standard operation is entirely practical. The Generation (Output) and Monitoring (Input) sections of the Test Chest 3 G ARE entirely independent, and share only the internal power supply rails. Generating 3G Colour Bars with embedded audio, whilst watching Composite Video and listening to balanced analogue stereo audio, for example, really is entirely practical!
Q: Can you explain, what is, and how to use, "clapper board"?
A: Clapper Board is a Test tool designed to check for, and evaluate, Programme Audio wrt ProgrammeVideo delay issues. In visual terms it consists of a simple horizontal Graticule with a Reference point (time 'zero') and a travelling Puck that repeatedly traverses from right to left; and in audio terms, an interrupted tone. When the travelling puck reaches time 'zero' the audio tone will be briefly interrupted, on each of the Embedded, AES and the Analogue OPs. This signal is offered on to a remote location, where it may be expected to have experienced a number of Video processing operations en-route, each of which may have involved Frame Storage; if the audio signal has not experienced an identical delay too, lip-sync problems are inevitable.
At the final receive point, the Clapper Board signal may be evaluated for V/A delay errors with nothing more sophisticated than a picture monitor and a loudspeaker. Because of the repetitive nature of the signal, it is very easy to assess delay errors visually, and (possibly) a finger slid across the viewing screen to act as a cursor. Small timing errors are immediately apparent to the Observer. Naturally, neither Test Chest 3G nor the Clapper Board signal are able to correct such errors directly, but the need for correction becomes immediately apparent, and steps iniated to adjust existing equipment appropriately.
Q: I've set up the Generator as I want it, but there appears to be no_Output?
A1: This is usually 'finger trouble'. Ensure that you have not inadvertently selected the TG3G's output to be "LOOP". This would set the TC3G to 'Equalise & Reclock' the input signal on BNC1, and "LOOP" it on to the OP BNC, thereby effectively bypassing the internal Generator.
A2: Ensure that you do not have "CLAPPER Bd" selected. Since this is inserted at the end of the Generation chain, just before the OP BNC, it would bypass the TC3G' internal TSG.
Q: Just how good are the output signals?
A1: All the SDI output signals are generated with 10 bit precision
A2: The Composite video signals (which will only be present when generating the 'SD' Standards 525 or 625) are generated with 8 bit precision, so Differential Gain and Phase are in the region of 0.5% DG and 0.5' DP.
Q: Just how 'fine' are the Horizontal and Vertical lines on the Grill pattern?
A1: 'Horizontal' lines will be '1 line thick' on progressive Standards, and 2 lines thick (1 on each Field) with Interlaced Standards.
A2: 'Vertical' lines will have the finest possible width, consistent with the bandwidth limitations for the Standard being used.
So, does this 'A2' answer mean that I can't have a 1 pixel wide vertical line? Yes, I'm afraid so; whilst electronically the digital output circuitry might indeed permit such a signal to be generated, the implied bandwidth requirements would be far outside the practical response of a conventional display device, and the viewed image would be masked with unpleasant ringing artifacts caused by these ultra-fast edges.
Monitoring.
Q: I have heard a lot about your “which-wire?”, what is it?
A: “Which-Wire?” mode is a powerful hands free utility, exclusive to Murraypro (and presented first on an earlier Murraypro Product) which enables you to automatically determine vital information about an input signal, such as whether it is actually present (or not!) and it's TV format and Standard, without you having to make any configuration adjustments what-so-ever.
Q: OK, sounds great! So how do I initiate, and use, this “Which-wire?” Mode?
A: Simple; first turn the Test Chest 3G OFF, using the main menu's 'Power' icon!
Next, apply your mystery video source to Test Chest 3G's “WW?” input. This is will be BNC #1, situated on the bottom-right corner of the front panel.
When a TV input signal IS PRESENT, the Test Chest 3G will automatically awaken from hibernation, and display the input signal on the LCD panel. It matters not what standard the input signal is, 3G-SDI, HD-SDI, SD-SDI or even CVBS, the image will be displayed in less than one second, together with a banner declaring the detected input Format and Standard which will remain displayed for 5 seconds. Pretty cool, eh?
A moment or two after the input signal is removed, the Test Chest 3G will automatically power-down and resume hibernation mode; ready for your next mystery source.
Q: If I leave the Test Chest monitoring in “WW?” mode, will it detect a change of input?
A: Yes, most certainly. The Test Chest 3G is continuously monitoring the input Standard, and any change will be instantly detected and displayed on the LCD's Banner display for 5 seconds.
In fact whilst the Unit is powered and in 'TV Monitor' or WFM mode, the detection is even faster than it is in normal “WW?” mode, as Test Chest 3G has already completed it's “detection of an input” test, so this initialisation is already complete; subsequent Standards detection of an IP source is effectively instantaneous, with no perceptible delay at all!
Q: Termination of video lines is always important, do I need to terminate the “WW?” input?
A: NO! The Test Chest 3G's BNC #1 is ALWAYS terminated in 75 ohms, and no external termination will be required. The BNC #1 has been configured by careful design to present a 75 ohm resistive port, with low return loss up to 3G clock frequencies. In fact, ONLY a precision BNC connector correctly fitted to an appropriate high grade coaxial cable such as Belden 1694A, or a direct equivalent, will return adequate performance at 3G frequencies; lower performance connectors/cable are very unlikely to remain acceptable and return satisfactory performance with the passage of time.
Q: Does the Test Chest 3G have any “unterminated video inputs?
A: YES, there is a high impedance input port (1M ohm + 20pF, nominal) associated with the Oscilloscope, using BNC #2.
Q: How do I align the trace with a graticule point for measurement, as Test Chest 3G does not appear to have any 'Shift' controls?
A: Simple really, just use the touch screen and your finger to 'drag' the trace to the desired screen location!
Q: How do I use the oscilloscope mode?
A: Be aware that the Oscilloscope Utility has a frequency response suitable for baseband audio & video extending to a high of about 10MHz (-1dB); SDI signals @ 270MHz and higher, are not suitable therefore for direct examination, but can produce a useful indication of their presence, due to the ADC's high speed sampling of the source.
The Oscilloscope input is BNC #2, and this presents an input impedance of 1M ohm in parallel with approximately 20pF. This represents a typical 'Scope input', and has been designed to interface directly with a 10X high impedance scope probe. Use of the 'Scope feature with a switchable 10X/1X probe will extend the amplitude range over which it is possible to obtain useful results.
Oscilloscope mode is selected via the “SCOPE” icon on the main menu.
Most of the input signals to be examined are likely to be audio or video related, so it is practical to use the Test Chest 3G's WFM 2V, V, 2H & H timebase ranges to cover low and higher sweep speeds.
Q: Can I use the Oscilloscope as an 'Audio Signal tracer'?
A: Yes, this is entirely practical using the Test Chest 3G's internal loudspeakers, or headphone socket.
After setting the Test Chest 3G to 'SCOPE' mode as described above, navigate away to the main menu and select the “Audio Mon” icon. Using the 'loudspeaker source selector' icon in the lower-left of the screen, toggle the icon until the LCD's top Banner declares "BNC IP”. This has forced the audio monitoring to monitor the WFM display, and the audio component of any waveform shown on the 'Scope display will now also be audible via the internal audio monitoring speakers subject to their intrinsic audio response, but use of the 3.5mm jack enables use of Hi-Fi headphones. Navigate back to the 'SCOPE' mode on the main menu, and use the Oscilloscope Utility as described previously. The main menu's increase/decrease icons may be used to control volume.
Q: How do I mute the front speakers, when I am using the external headphone socket?
A: Simple, Test Chest 3G detects to use of low resistance external headphones (30R – 600R), and automatically mutes the stereo speaker drive stage when you jack in. Be aware that this muting does not occur as a direct result of the insertion of a 3.5mm Jack, and a disconnected 3.5mm jack, or very high impedance headphones, will not initiate muting if they are inserted alone.
Q: How do I use the TDR/Cable test?
A: The 'Cable Test' feature employs Time Domain Reflectometry, launching a short duration pulse from a 75 ohm source impedance into the cable to be tested, and detecting reflections caused by impedance matching errors along the coaxial cable. Ideally, with perfectly matched and terminated cable on the TDR port, BNC #3, there should be no reflected energy at all to view.
The 30nS TDR pulse contains frequency components up to about 130MHz, and iterative impedance errors will be visible as a modulation of the steady state value of the trace following the launch of the TDR pulse which is always displayed on the left side of the trace, at time-value 'zero'. A subsequent positive excursion indicates the presence of an impedance higher than 75ohms, whilst a negative excursion indicates a lower impedance. The timebase of this display is calibrated in metres for Belden 1694A cable, so the distance down the cable to any iterative impedance error may be determined by direct examination of the glitch's position on the X trace.
Q: How can I use the TDR on long cables?
A: The TDR display page offers three pulse width options, a narrow pulses for shorter cables (16 & 32nS), and a significantly wider (64nS) pulse for use with longer cables.
The TDR feature detects and displays energy reflected from iterative impedance errors, and in most case the amplitude of a reflection will be rather small. Any reflection(s) will always result from energy that has travelled along the cable twice, ie there and back,so it will always become increasingly attenuated as the cable length increases.
For longer cables a compromise is necessary between fault resolution and the ability to detect errors at all, due to the significant cable losses. The wide pulse option launches significantly more energy, but with a lower frequency spectrum that extends up to around 25MHz into the coaxial cable, but at the expense of the ability to resolve fine detail. Be aware that for any reflection shown at 600 metres on the Test Chest 3G's TDR display, the energy will have travelled nearly 1.25KM, and will have become significantly attenuated!
Q: Sometimes some picture lines appear to be 'missing' when I look at very fine detail, such as the Grill Test Signal, why is this?
A: Essentially the Test Chest 3G's native TV display is 800 x 480 pixels, and all the input signals to be displayed must be 'processed' to fit this format. If this were not done, a very significant amount of a 1280 x 768 picture would be outside the scanned area, and most of a 1920 x 1080 Format picture would be lost! Design decisions have been made, consistent with the minimum processing overhead, image latency and power consumption, which produce acceptable SD, HD-720, HD-1080 & 3G images without the overhead of digital multipliers; and inevitably this results in slightly compromised interpolation.
Q: How do I monitor an AES input'?
A: The TDR feature and AES input signals share BNC #3, which is always terminated in 75 ohms.
Navigate via the main menu's 'Audio Monitor' icon to that page, and then select the 'AES' icon which presets the Test Chest 3G to expect an AES audio source for monitoring. Note that the AES BNC #3 input port is optimised for use with a 1V pp signal (nominal) on coaxial cable with a 75 ohm iterative impedance; see below for use with 110 ohm balanced sources on XLR3.
Q: How can I accurately match an XLR's 'Balanced 110 ohm AES input' to BNC #3's 75 ohm Port?
A: Simple! The Test Chest 3G's Audio-POD (and the Rack-mounted “Test Chest 3G-R”) contains a Utility AES matching transformer which is designed for this application.
Connect the Audio-POD to the Test Chest 3G, and lock it firmly in position using the 'over centre' toggle latch to securely clamp on to the TC3G case just behind BNC #2. Feed the Balanced AES into the XLR3-F of the matching transformer, and route the BNC output to the Test Chest 3G's BNC #3.
This transformer is reversible, and can also be used to match the TC3G's balanced 110R OP for 75R unbalanced operation.
Q: Do the balanced audio inputs and outputs terminate in 600 ohms?
A: NO, most certainly not! The audio inputs on Test Chest 3G are always high impedance. Terminating audio equipment in 600 ohms is not current audio practice, and is very seldom required these days. The output impedance of the Test Chest 3G audio ports are low, about 30 ohms, and these should NOT be terminated in 600 ohms either, or subsequent amplitude loading errors will occur.
This 'low impedance out' & 'high impedance in' concept is used on all Murraypro Equipment, and enables several high impedance loads to be satisfactorily fed from a single output port without any amplitude issues occurring due to loading. Termination loading errors in a 600 ohm environment can easily result in a line amplitude being either 6dB high, or 3dB low, an amplitude swing of 9dB!
Q: Why doesn't Test Chest 3G offer an “Eye” display?
A: Currently, we do not intend to offer an “Eye” feature, and there are several important reasons for this:-
All an "Eye diagram" actually shows is the HF loss/distance on a coax cable, and this after all is basic physics, nothing more. In order to function practically, ALL SDI systems have to incorporate an 'input equaliser', so the input signal is always used post-equalisation, and ONLY correctly equalised signals are ever processed in TV's 'real world'.
The ONLY thing that matters therefore is the quality of the signal after equalisation, not before; and this will be a direct function of the performance of the input equaliser stage used in any particular SDI equipment, ...so why attempt to examine such a soggy, tatty and unequalised signal?
It is by no means certain that the equaliser performance in the measuring instrument would be identical with that used in Proprietary Broadcast equipment such as that from JVC, Panasonic or Sony for example, in fact it is highly probable that they are NOT identical. It is no use the Measuring Device using very latest IC which equalises (perhaps) 250M cable, if the Equipment in general use on the Station uses earlier generation devices which might only compensate for perhaps 100M of your chosen Reference Coax!
The “Eye's” input PCB layout and Analogue Digital Convertor need to have a exceptionally wide bandwidth with high phase linearity if the display is to be accurate; and figures of 10GHz have been suggested for realistic fidelity. How much of a perceived rise/fall time inequality, or a displayed ringing problem are actually due to the input stages of the measurement device? At Murraypro we are well aware of the technical difficulties involved with producing an acceptably low return loss at 'only' 2.8GHz; and even this can only be achieved through the use of the very highest quality BNC connectors. The compromised performance of the Bayonet-Neill-Concelman connector (BNC) is a serious issue at only 2 or 3 GHz, and why high frequency Spectrum Analysers have shun this 60 year old design in favour of 'N' Series connectors; and that the performance of the optional "Eye" feature offered by at least one of the Test Chest 3G's competitors is highly dubious.
The Test Chest 3G's TDR cable test has the fundamental advantage of using the Installation's actual equipment and it's input coax cable together with their own BNC connectors as the actual terminating load, rather than the temporary imposition of the input of a measurement device, which is quite alien to the normal configuration of circuit under test. Consider the 'Real World' case reported below where investigation of a problem, using the TDR's 32nS pulse, instantly revealed the imperfect mating of a poor quality BNC connection at the end of a 100M run of high quality coaxial cable. It is most unlikely that an "Eye"waveform could have localised this problem in this way, or indeed even being capable of showing it at all; let alone, as the Test Chest 3G did, localising the fault precisely, and in a matter of seconds!
The ultra fast ADC devices that are required to produce any sort of realistic “Eye” display are power hungry, and their use has an adverse effect on battery duration. Additionally these ADC may require a dedicated input port, and with some implementations these are offered as a separate module Option, which is always available at significant extra cost. Not so with Test Chest 3G, where our TDR feature is complementary and is included in the standard Unit!
Q: Can I use the Test Chest 3G to show proximity to the 'digital cliff'?
A: Yes, by using the “SDI CAL” feature on the Set Up sub-menu page, which is accessed via the 'Spanner' icon of the main menu. Different TV Standards will have differing Clock frequencies, 270MB/S, 1.4GB/S or 2.8GB/S, and different Installations will have been installed with differing types of coaxial cable. Cable losses at System Clock Rate may therefore vary considerably from Installation to Installation in absolute terms, whilst remaining entirely satisfactory in their own right for that particular Installation.
i) Set the Test Chest 3G to Generate a Colour Bar signal on the TV Standard appropriate to the Installation under evaluation.
ii) Select coaxial cable of the type in use on that Installation being tested, and of a length that your local tests have shown are approaching the “Cliff”. Conventionally this is usually determined by evaluating performance of a piece of equipment down a nominal length of the cable selected, and then experimentally extending the cable, in increments of perhaps 10Metres (using a BNC Barrel), and then evaluating for deteriorated performance, as an increased 'Bit Error Rate' (BER).
iii) This process is repeated until the system fails to operate normally. This is the so-called digital “Cliff” and, at this point, performance deterioration will be very rapid with only small increases of total cable length.
iv) Ensure that this test is always performed with samples of the Equipment in use in the Installation under test, rather than the Test Chest 3G's own Which-Wire? SDI input, for reasons explained earlier.
v) Murraypro recommend that the 'SDI Cal' length is set conservatively, rather than at maximum length achievable, so that it acts as an “EARLY WARNING” rather than an “UNDER ATTACK” alarm! Be aware that the Test Chest 3G's own Equaliser uses the latest high performance '3G' device type, which offers significantly enhanced performance over earlier devices, and consequently could suggest unrealistically optimistic cable lengths, compared with your own existing equipment's performance.
Knowing the maximum cable length, before compromised performance is likely to occur, enables the User to pre-load and calibrate the Test Chest 3G's “SDI CAL” feature realistically to warn Users of cable lengths that are likely to be approaching this critical length.
To align the “SDI CAL” feature for your particular Reference Cable as selected in paragraph 3, simply loop the Colour Bar SDI OP (BNC #5) as set for earlier in paragraph 2 of this topic, back to the Which-Wire? Input (BNC #1) using the Reference length of coaxial cable and tap the “SDI CAL” icon on the setup sub-menu. This will memorise the current SDI Input Equaliser's AGC voltage, enabling direct comparison with other cable lengths in the future. These comparisons are indicated as “Short” when shorter than your Reference Cable; and “Long” when the local input cable exceeds that Reference Length.
Q: Do you have a list of the TV Standards covered?
Standards available:-
3G 1920x1080: 50Hz Progressive (A)
3G 1920x1080: 59.94Hz Progressive (A)
3G 1920x1080: 60Hz Progressive (A)
HD 1920x1080: 23.97Hz Progressive
24Hz Progressive
25Hz Progressive
29.97Hz Progressive
30Hz Progressive
47.95Hz Interlace
50Hz Interlace
59.94Hz Interlace
60Hz Interlace
HD 1280x768: 50Hz Progressive
59.94Hz Progressive
60Hz Progressive
SD 625: 50Hz Interlace SDI
50Hz Interlace CVBS
SD 525: 59.94Hz Interlace SDI
59.94Hz Interlace CVBS
Q: Do you have a list of the Signals Test Chest 3G can generate?
A: The Test Chest 3G is intended for use in the Field, rather than use for Product Development in a Lab, and consequently it offers a range of popular Test Signals. All the signals are available virtually instantly, and on all supported TV Standards, and either the 'Y', 'Ch', or Both components may be independently disabled.
100.0.100.0 Colour Bars
100.0.100.0 Red patch Colour Bars
100.0.75.0 Colour Bars
100.0.100.0 Red Field
100.0.0.0 White Field
Grill
Multi-burst
Augmented Pulse and Bar
Bow-Tie
Stair Case, 5 step.
Limit Ramp
Limit Ramp + modulation.
Pathological Test Signal.
Pluge
SMPTE Colour Test field
It must be appreciated that Multiburst (etc) envelope specification will vary appropriately with the set Standard. When set for operation on "SD" Standards, a CVBS OP is available in parallel with the SDI OP.
All Signals may have either 16:9 or 4:3 circle added, and a moving Puck to check for frozen (MPEG) processing elsewhere.
A Clapper Board signal is generated to check for downstream video/audio processing delay inequality.
Although not a Test Signal in the same TV sense, the Test Chest 3G also offers three test pulse widths for TDR testing, via the BNC3 port.
Please feel free to ask further questions, if the above response is insufficient for your requirement. E: tech@murraypro.com
The Test Chest 3G is a developing Product and we are anxious to enhance it in line with User's requirements, therefore we are always pleased to receive feedback regarding 'Requirements' or 'Wish List'. Whilst we can not undertake to incorporate specific requests, we always consider Client feedback very carefully. All constructive feedback is extremely valuable, whether it is favourable to us, or otherwise.
E & OE
Tony Drummond-Murray
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©Murraypro November 2011