Cause of return loss in cat5e cable

One of our biggest suppliers asked us to test a sample of cat5e cable - we tried a couple of different RJ45 ends on the cable - a non-name one and Tyco. We ran the same 1000BaseT test on all six cores for both connector types and if you look you'll see that cores 2 & 4 consistently fail on return loss.
I initially thought it must be down to badly terminated ends but the DTX makes a distinction between return loss over the length of the cable and return loss at the remote end (how on earth it works that put is anyone's guess!) - generic RL is therefore all the reflections along the whole length of the cable that impede the transmitter's ability to send a strong signal.


Now then - it's the brown pair in every case - that suggests that the brown pair is sub spec. We didn't test to an ISO standard (because the cable isn't marked with one) so we used a generic gigabit Ethernet test which is a bit more tolerant.

I have to say I think the cable has a manufacturing fault in the brown pair.


With that in mind we stripped out some of the brown pair from core 2 (bad) and core 5 (good) and you can see the twist in the bad pair is much more variable than the twist ratio in the good pair.

So - it seems like the brown pair in cores 2 and 4 is inconsistently twisted compared to the brown in the other cores.

The great 3G cable shoot-out

Thanks to Simon Hillman for tabulating them in a way that makes trends clear. The link in the title is the directory with the A1 plots.

The tests based on a pathological signal are more extensive and test for six cable types - three HD and three SD. Since we were trying to spot trends due to cable length we feel this is the most informative of the sets of data. Simon re-did a subset using only the three HD types and 1080/50P colour bars to test for jitter which (as you'd expect) doesn't vary to any degree with length but you can see the relative damage barrels and U-Links do.

The conclusions that spring out are;

• At 3G using coax specified for HD 60m seems to be the workable cable length before attenuation becomes an issue and the eye closes below 400mV.
  
  
• SD coax goes about half the distance - this seems counter-intuitive as most SD coax has a notional analogue bandwidth (+/- 6dBs) of 360Mhz - three octave less than HD coax. Clearly the signal recovery in the WFM8300 is at play.
  
  
• The variation between the best (most expensive) and worst cable at HD before the signal becomes sub-optimal (i.e. worse than 3dBs attenuation) is less than 10m with Belden 1694 coming out on top.
  
  
• The 8300 was still able to recover a signal at 150m with Belden but only 120m with the Draka DC DVC13C. At these length the mean time between corrupt video frames would be unacceptable.
  
  
• The Condufil 1694-equivelent tracks the more expensive Belden cable very well.

As mentioned this was really a test of run-lengths for a practical guide to cabling TV facilities. In the bulk of the tests we used the correct BNC crimp connectors and the proper tools for the brands of BNCs (attached by an experienced wireman) - We did try and provoke jitter by mixing up connectors with cable but it seemed to make scant difference. It does seem for 3G HD video the newer style 4.5Ghz are to be preferred over the original HD-type cable.

In the end I suspect that these results will represent the best possible world as Tektronix gear is known to drive a coax line optimally and has excellent return loss on its inputs. Other manufactures are less so and if our experience with 1.48G 4:2:2 HD is anything to go by the massive variation in the quality of line-drivers and receivers will make these results meaningless. Nobody (particularly in these hard economic times) builds a facility with only Sony and Tektronix equipment.

Many thanks to Tom & Lee at Tek for the loan of the equipment and advice and Simon and Graham at Bryant for providing the various cable types, ends & tools. Please note all original information and test results are the property and copyright of root6

3G cable 'shoot-out'

Three gigabit HD-SDi video has been around for a couple of years now but I've yet to see a comprehensive review of different cable types and how they handle the newer 1080p50 signals. Bryant Broadcast contacted me a couple of months ago and asked if I could conduct a test of the six cable types they recommend for HD work. So, I've borrow a brand new Tek WFM8300 (launched at IBC, not that I'd have known!) and have six drums of cable and all the BNC ends and appropriate crimp tools at the ready! I'll be measuring jitter, noise and the overall state of the eye pattern at 10m intervals from 200m down to 10m and then when we have a good feel for the various cable types we'll turn our attention to the damage that jackfields, u-links and BNC couplers do to the signal.
The image above is a screen capture of the machine with 2m of Belden 1694 cable - rated at 4.5Ghz!

I want to like Blackmagic

If you’re tired of hard to use and ugly waveform monitoring, then you’ll love Blackmagic UltraScope. We have included all the features you need when editing or color correcting, and then, combined it with an elegant user interface that looks great when added to your studio!

The reason some things are hard to use is that they are complicated - like video test and measurement. The reason Fisher Price don't make television test gear is because it's not for children! Anyhow - I sat down to have a tinker with this new gadget (in fact it's a PCI-e card you put in a spare computer) - it then hijacks the Windows desktop and runs full-screen. I don't imagine anyone would be willing to sacrifice one of their Avid or FCP monitors (aside from the fact that you'd be taking at least a couple of lanes of PCI-e bandwidth and hence making a non-supported config).

It is surprisingly uninspiring - you get only what you see - you can't move anything around or zoom in either direction. You have no measurement graticules and non of the features that are necessary in a modern rasteriser. It really is just the facade of a waveform monitor but when you look harder it is kind of useless. Seriously - save your money because this is pretty pointless. It might make a nice display for reception.

Contemporary MPEG4-derived video codecs

For some applications, getting it wrong – or not fully optimal – the first time can be very expensive. For example, when making a semiconductor, it is very expensive to re-make masks. Plus, of course, if the semiconductor has already been put into another device, such as a camera, or mobile phone, or set-top box – it is too late (except perhaps for software workarounds). Also, in the field of semiconductors, there is a trade-off of extra silicon area for more advanced processing, versus the cost of designing and supplying a larger chip.

Another excellent primer from Tek - well worth reading if you're involved in digital video delivery.

Loudness Measurement

This how to guide highlights the benefits of the Loudness Measurements software on the WFM6000/7000 series and WVR6000/7000 series products.
Until NAB this year (when Tek introduced this update) the predominant way to measure perceived audio loudness was with some propriety instrument like the Chromatec (approved by Channel Four). Tek have done the right thing and not only followed Ofcomm's new guidelines but they've devised a scale that is as easy to read/understand as a PPM.

Hopefully they'll do the same thing with PSE measurement and put Harding out of business!

Tektronix - why they really are STILL the best! pt.1

I often say that customers only ever avoid buying Tek because they can't afford them - nobody ever says "...I need a Hamlet/VideoTek/Leader etc." because it's the best solution, rather it's cheaper than Tek. However - in the last year they've had the WVR/WFM 5000 range which puts pay to even that.

Anyway - last week I went to their Vision '09 day - a kind of pre-NAB training day for users and dealers. They ran four sessions.

Upgrades to WVR/WFM-series 'scopes

• ANC data - the HD-SDi ancilliary data stream can now encompass user-defined type. So, you could make a new ANC-type called whatever you like and as long as you know the pre-amble values you can have the Session Data page watch for those packets. Very useful if you wanted to individually mark the output of encoders and then check to see which machine made an HD-SDi stream. I suggested it to Root6's Dev team for Content Agent.
  
• Dolby information - On the Audio Session tile you can now see the values for the DolbyE metadata - Dialogue Normalisation, Dynamic range and Downmix. You can also check the the guardband figure to see if the embedded DolbyE data is locked to video.
  
• Black/Frozen - this is a new parameter in the video QC section - previously you could check for extended periods of silence on the audio but now the instrument can check for frozen or extended periods of black - it's window'able as well so you can check if the lower-third financial ticker (for example) has frozen despite the studio video continuing.
  
• Infinite Persistence - you can turn any display into a storage 'scope - useful for checking for those extreme events that occur rarely.
  
• AFD - a few more vertical-interval signals (although they're now rolled in with the ANC data) can be detected - widescreen flag, V-chip, etc.
  

Overall a superb set of features which come for free (just download the updater) - WFMs can do it off the USB socket on the front, WVR machines over the network. This will all be available after NAB.

Ofcom and PSE - there is no secret sauce Mr Harding!

The issue of Photosensitive Epilepsy comes up often in television - back in the late nineties there was an episode of Pokemon that featured flashing images that provoked kids in Japan to have seizures. Since then Ofcom have been very keen to avoid this on British television and since 2003 have produced the following guidelines;

OFCOM Guidance(extract).pdf

This is an extract from the document but it does include the important details which hinge around the following;

3. A potentially harmful flash occurs when there is a pair of opposing changes in luminance (i.e., an increase in luminance followed by a decrease, or a decrease followed by an increase) of 20 candelas per square metre (cd.m-2) or more (see
notes 1 and 2). This applies only when the screen luminance of the darker image is below 160 cd.m-2. Irrespective of luminance, a transition to or from a saturated red is also potentially harmful.

3.1.1. Isolated single, double, or triple flashes are acceptable, but a sequence of flashes is not permitted when both the following occur:
i. the combined area of flashes occurring concurrently occupies more than one quarter of the displayed (see note 3) screen area; and
ii. there are more than three flashes within any one-second period. For clarification, successive flashes for which the leading edges are separated by 9 frames or more are acceptable, irrespective of their brightness or screen area.

These parameters are well defined and so anyone who can understand them can build a PSE detector that will with certainty detect when a violation occurs. This is how the situation should be as it avoids any one manufacturer of test equipment having a monopoly. Unfortunately this is just the situation that has nearly developed with the Harding FPA detector. Their machine is a PC with SDi capture card that you digitise the video sequence to be checked into and it runs an analysis. The other popular unit is the GordonHD which is more like a traditional piece of equipment in that it sits in the signal chain and gives an alert when it sees a violating sequence go past.

We have a couple of customers who like the idea of realtime performance that the Gordon gives and don't like having to capture (the Harding doesn't support standard codecs so no Quicktime reference export from Avid!), analyse (in slower-than-realtime) and then get a report - only to repeat it all after you've corrected the offending clips (because the broadcaster likes to see a full 10:00:00:00 - 10:54:00:00 report!). The Gordon on the other hand is cheap (£3k against £13k) and just sits there taking a feed of HD/SDi video and Timecode and firing a GPI when a violation is detected (and even entering the TC into a file) which means you can have it hanging off the Avid (or whatever) and the editor can rock'n'roll over a piece of footage adjusting his edit point over the flash frames (it's mostly paparazzi footage with all those camera flashes that cause it) until he gets a sequence that doesn't cause a problem.

Anyhow - you can tell which machine I think is best. Harding is a great self-publiciser who gives you the idea that he alone knows the secret-sauce of PSE. The guys at Tektronix tell me it's on the way as an upgrade for their WVR-series 'scopes but they are worried that Harding has all the patents stitched up.

Anyway - a quick once around pals revealed the following;
Ascent Media check all of five's output (including the two daughter channels) on a GordonHD, ITV's QC department at Upper Ground use a Gordon as their first-pass analyser and Channel Four specify it as well. However, talking to everyone in facilities reveals that they (almost) universally believe the Harding to be the only machine capable of doing the job.
I had several earlier-model Gordon's at Resolution and they were superbly fitted to the job (and cheap enough to have one in every suite). We never had a tape sent back that had gone through it and that included many more hours of terrestrial television than most facilities ever turn out (including quick turn-around stuff with lots of potential trouble - think the Friday night eviction show for Big Brother).

John Emmett of BPR is a gentleman of the old school (they make the Gordon) and you can find an interesting paper on the subject of PSE he co-authored here.

WFM7100 screen grabs

I'm currently prep'ing some training notes for video, audio & QC test and measurement. I've often said it, but Tektronix really are the best-of-breed for television signal monitoring. People only buy Hamlet, Harris, Videotek etc. because they won't stretch to a Tek.
So, here are some screen grabs - handsome!

Eyeheight legalisers parameter bugs

I came across this a couple of years ago - if you recall the Rec103 preset the ringing perfromace is wrong!
Here is the email I got from their tech support back in September 2006 and the one I installed a couple of days ago is still suffering!

...this is a software bug which we have just noticed and are now working on. We should have a fix within the next few weeks.

In the interim you could enter the values for the EBU settings you require manually. You could even store these values into memories and label them as explained in....

http://www.eyeheight.com/manuals/systemHardware/evolutionDT_platform_user_manual.pdf

Here are the values for the various presets....

Memory 1 Legaliser On 0% - 100%

Memory 2 1. Set High Clip = 105%

EBU 103, 2. Set Low Clip = -5%

Tight 3. Set Ring Suppression to "MANUAL"

4. Set High Ring Threshold = 103%

5. Set Low Ring Threshold = -1%

Memory 3 1. Set High Clip = 103%

EBU 103, 2. Set Low Clip = -3%

Optim' 3. Set Ring Suspression to "MANUAL"

4. Set High Ring Threshold = 101%

5. Set Low Ring Threshold = 0

Memory 4 Bypass / Legaliser Off.

....hope this helps and we will contact you with the software up-date files which you can flash into your legaliser using the RS232 port of a PC.

BBC64 camera line-up 'chip-chart'

I'm at the studio build today setting up camera channels and doing general line-up. We've supplied the good-old BBC64 camera chart which I used to spend many happy hours staring at whilst lining-up cameras for studio/OB shoots. When I die (and they lay me to rest....) I want this and Test Card F on my gravestone!
The info sheet has all the reflectance figures and frequency gratings for when you have the camera focused full-frame on the chart.
Oh, does anyone know why the light-trap in the middle of the chart is called a Gregory Hole?
Also - ex-BBC type, can you still get hold of Cardboard Kate?

Tektronix WVR7120 audio pinouts

Why do Tek lock their PDFs?!

Tektronix WVR7100 & NTSC gamut in HD

Talking about NTSC colour gamut on an HD recording seems a nonsense (how could something in 709 colour space have any relation to composite legality?) - however, since Sky take delivery on HD-Cam (and increasingly SR) they insist that all recordings also conform to a composite colour space. For those recordings in 29.97 and 59.94 it's an NTSC colour space they need to also conform to. This seems a bit daft to me - knobble your nice HD production so we don't have to worry about it. Surely the best way would be to transmit the HD and then stick a legaliser across the down-converted output rather than making the HD master conform to a small colour space so that down-conversion is easier. Talk about casting your pearls before swine!

Anyhow - one of our customers uses Tektronix WVR7100 rasteriser waveform monitors and has been QC'ing for delivery to Sky and noticed that with an NTSC master (either SD or HD) the Tek consistently throws composite gamut errors. The second screen-grab shows that the legaliser feeding the Tek has had the colour gamut wound right down (see how cropped the two diagonals on the arrow-head are) yet the 'scope continues to flag errors. It even does this with monochrome material!
So - I have to get on to Tek. The problem isn't there on 24, 25 or 50i material, just NTSC-derived stuff.

Upgrading a Tek WFM7100

I demo Tektronix monitoring products and today I had to upgrade our loaner WFM7100. I'd done software on these chaps before and you can either do it over the web interface or via a USB stick on the front panel. In the case of this version 3.0 update (from the previous v1.25) you have to replace the front control panel, update the boot loader over the network and then use the USB stick to upgrade the instrement.

It's quite a change - it's made it into a WVR7100!
It seems a lot more stable and quicker. Also - it's not a touch-screen any more - it has the same front panel button set as a WVR (but arranged around the display). Using the Java app to control it you can't tell it apart from a WVR. Amazingly Tek ship this upgrade kit for free - given how well made the new front panel is I imagine they are taking a hit of hundreds of pounds per customer update.

I was tickled to see the attached label on the USB stick - you might kill your machine by doing the upgrade and if you do we'll bill you to fix it! I can report the update was entirely successful!
Actually - Tek upgrade procedures are always entirely straighforward and the instructions never leave anything to chance.

Another cool feature is that (being a dual-link HD-SDi machine) it now supports dual live inputs (at YUV 4:2:2, not RGB 4:4:4!) so you can be monitoring two video signals at once!

Tektronix WFM7100

I've just my hands our new Tek WFM7100 demo unit and after one quick firmware update (to v. 1.23, fact fans!) I've been monkeying about with it ('cause I'll be demo'ing it post IBC). First thoughts are that it's very sluggish - screen update on waveforms is fine but navigation is slow. It feels like i's running on top of something (Windows Embedded?!) and that seems to be born out by the fact that when you hit it over the Java interface the menu on the front panel screen remains with the last selection you made and the remote display changes as per selections you make on the browser - almost like a remote desktop.
Anyhow - feature wise it is pretty much a WVR7100 with some nice extras. The biggest step is the screen grab facilities. In the same way that video or audio 'events' (gamut, level etc.) can be placed in the log, close the GPI, honk an SNMP alarm or just indicate on the front panel you can now have an error condition dump a screen-grab to a USB thumb drive. Now you can imagine exporting the XML log with still-frames of the offending video - excellent for monitoring the state of a cable head-end (for example). Another addition is having a picture o/p SVGA as well as the instrement's display out. We often install the WVR series rasterisers into machines rooms and DA the feed to several places (including for the operator in the machine area) - but since this has a built-in insterment display it would be advantageous to have just the picture (on a 15¨ TFT panel) thus avoiding the cost of an HD monitor.
Unlike glass-tubed traditional 'scopes (and even some other rasterised models - specifically the Videoteks) the 7100 generates the graticules in the same digital space where the HD/SDi stream is demultiplex'ed - the upshot of this is that they are ultimately accurate - something no other 'scope can lay claim to (unless they've just been calibrated!). Having spent time doing a head-to-head with the other manufacturers (Videotek, Omnitek and Hamlet) I conclude that the only reason folks don't buy Tek is the price. In terms of accuracy, ease of use and feature set the Tectonix are way out in front. Their automated QC features are pretty impressive and make delivery reports very easy to prepare.

Tektronics HD measurement book

Engineers like me who grew up in the eighties/nineties will remember with great fondness the two Tektronics books "Solving the component puzzle" and the "Guide to Digital Video" - at the BBC they were included as part of the standard training syllabus. Anyhow - this is the HiDef one which ain't freely available, but as a Tek reseller we get it.

Decklink video cards and the online community they run at Creative Cow. I have been caught out several times by their so called "Pro" products - see a previous post here. Anyhow, I posted the following;

Does anyone have any advice on phasing the active picture to sync timing on the output of a Pro card under V4.7 of the driver on a G5?
I've recently put in a couple of suites running FCP 4.5 and the output of both cards shows a consistent error in their picture sync timing. It's so bad that some outboard devices (typ. those that don't have a separate genlock - a legaliser in this case) aren't happy with the SDi out.



Internal bars on a DVW A500P and the o/p of the Decklink Pro card
click the image for full size screen-grab from a WVR610.

You'll see the difference between the output of a DigiBeta (I'm assuming that is correct!) and the Decklink. What the Tek610 waveform monitor is showing is the difference between start of the data interval in the back porch and the start of active video. Although this isn't well specified in REC601 it is related to the 10.4uS interval that engineers measure to get the start of active picture placed correctly (dropping edge of sync to start of active line). In each of these screen-shots the Tek is free-running (so as to remove the effect of a card whose output isn't genlocked to station black). To make it a fair comparison I also pulled the reference from the VTR's input. There is about a micro-second of discrepancy.
It's wrong - measurably so - and is problematic if you want to integrate your FCP into a broadcast setup.

Now the moderator didn't put the post up but I was tickled by the following thread:

Subject: 4:3 to 16:9 (Letterboxing) Without Image Degradation

This may not be the right forum for this question, but thought I'd pose the question just the same: Does anyone out there know of an app that transforms non-anamorphic DV material shot at 4:3 to 16:9 WITHOUT just cutting off the top and bottom of the frame and losing all those valuable, indispensable little pixels in the process? Since I believe the Pana DVX100a does this digitally, perhaps there's some software that does it after the fact.

Thanks,

What you describe is impossible. To get from 4:3 to 16:9 you must lose part of the picture. The Panasonic camera just crops the picture, unlike other anamorphic systems.

In any event After Effects will do a better job than FCP, picture-quality-wise

I was afraid it was, but thought I'd ask anyway, since what might be impossible today, might not tomorrow. Thanks for the response.

Not a matter of possible/impossible, just a matter of simple geometry. Think about it: How can you change the aspect ratio to a wider ratio without cropping or stretching the picture?

Maybe they're not ready for measurements that mention microseconds!

TV Gamut - here is a bit I wrote for our work email newletter that we send to clients periodically.

A lot of the standards we adhere to in television today have their origins in the methods established in the dark days of early colour in the sixties. Back then there were no digital pictures, all images were sourced through analogue tubed cameras, telecine and slide scanners. Our world was either RGB (the red, green and blue colour component signals that came out of a camera) or composite (typically the output of VTRs and studios and what was sent to the viewer at home). The relationships were well defined and the graceful behaviour of analogue electronics meant that keeping pictures within the range that the VTR (and hence the transmission chain) could handle wasn't hard.
In the mid seventies the digital framestore started to make an appearance making possible digital video effects (DVE), electronic caption generators and painting systems (Paintbox, Matisse etc.). By the late eighties Silicon Graphics et al ensured that a lot of what we saw on screen was digitally originated rather than coming from 'real world' pictures. Now - properly designed digital systems are more than able to capture the full range of analogue colours (the gamut of the system) but a lot of strange un-analogue things can go on in the digital domain if care isn't taken. A digital signal can go from zero to full level in the space of a single pixel which could never happen in the analogue domain - the size of the scanning spot on an analogue telecine or the spot aperture in a studio camera ensure a more graceful response. You can also get very bizarre combinations of colours in the digital domain that would not equate to colours that came out of a camera. If you consider that the majority of the permutations of the ten-bit digital Y, Cr, Cb colour component signals that most contemporary TV systems store give rise to illegal colours then the pervasive nature of the problem becomes apparent. Add into the mix prosumer DV cameras where the pictures haven't had the caring eyes of a racks engineer looking at them as the were acquired and you'd be forgiven for thinking that getting your master tape past the broadcaster's QC department was well nigh impossible. Well there are two kinds of gadgets that allow us to avoid the pitfalls of bad gamut - waveform monitors and legalisers. With a waveform monitor you can keep an eye on the various parameters that make up a video signal. The best of breed come from Tektronics who have devised various display modes that make gamut errors very clear. The Diamond and Arrowhead modes are only found on Tek units and show clearly when pictures are getting near to gamut limits. The newer rasterised models allow several displays to be shown on screen simultaneously. They will also keep an automated eye on dozens of aspects of your video (and audio) and record them to a log file for later reference. Go for lunch and glance through the tape log when you get back!
If you mention legalisers to those online editors who remember the early models from fifteen years ago you'd be forgiven for imagining such devices only exist to make pictures look bad! It is true that initially they dealt with gamut errors in a very brutal 'digital' style but the last decade has seen much more subtle methods and now a lot of broadcast television (particularly fast-turnaround shows with lots of DV or other domestic content) goes via a legaliser before transmission. They hardly ever effect the looks of pictures (so long as you don't go for particularly garish red captions!) but your pictures are now guaranteed to be 'street legal'. The models we've found to be most effective are from Eyeheight whom we sell for.
Root6 has spent time researching both legalisers and waveform monitors and we believe we offer best-of-breed examples of both at standard and high definition. Please call for details, a demo or advice on both of these.