Order of the Bath

Cat5, Cat5e and Cat6 standards of network cabling are commonly used for computer networks but can also be used for other purposes such as telephone, and video. They were originally rated at 10Mb, 100Mb and 1Gb respectively but the limits have all been pushed.

The cable

The cable itself consists of four twisted pairs of wires. By convention these are numbered 1 = Blue (Bl), 2 = Orange (Or), 3 = Green (Gr) and 4 = Brown (Br). Each pair has one wire in a solid colour and one striped with white and the important feature is the twisting which gives it the high bandwidth and low cross talk characteristics. Normally this will be unshielded though shielded and individually screened are sometimes seen in hostile conditions. The difference for Cat6 is that the pairs are separated in the cable by a plastic cross partition, the wiring is the same. No connection should be more than 100m long with (ideally) no more than 10m of that being patch cables. There should be no kinks with bends with a radius of no less than 25mm. Use Velcro cable ties if possible as the normal ratchet ones squeeze the cables too tightly.

The connectors

The connectors are flat and latched on the wide face, called RJ45 (unlike UK telephone plugs which are latched on the short edge). There are variations for each Cat level so be sure to get the right type. Looking at the top (flat) face with the cable towards you, the pins are numbered 1 to 8 from the left. It is important that the twists in the pairs are maintained as close as possible to the connectors.

The T568B standard is the most common wiring pattern, and that is what I will assume for this article.The A version of the standard interchanges pairs 2 and 3 (orange and green). T568A can be used so long as you are consistent within any one installation and the standards people say that the A scheme should be used for all new installations but everyone seems to ignore them. Pre-made patch cables are invariably to the B scheme but, as I said before, it still doesn’t matter which you use so long as each run is the same both ends. See how your patch panels are wired before deciding.

The T568B pattern

pair 2    pair 3    pair 1    pair 4
W/Or Or   W/Gr Gr   W/Bl Bl   W/Br Br
1    2    3    6    5    4    7    8

Looking at the top of the plug, this comes out as

W/Or Or   W/Gr Bl   W/Bl Gr   W/Br Br
1    2    3    4    5    6    7    8

Sockets vary in how they are set up. many should be connected

Or   W/Or W/Gr W/Bl Bl   Gr   Br   W/Br
2    1    3    5    4    6    8    7

The reason for the difference is that there are internal twists inside to maintain the performance. Others use punch-down blocks like the patch panels below. For T568A conventions, interchange the orange and green pairs in all of the above.

Patch-panels often use a punch-down block with coloured markers. The striped wire goes first (on the left) when in the normal BLOG order (BLue, Orange, Green, brown). Again, the internal wiring sorts out the order on the pins.

pair 1    pair 2    pair 3    pair 4
W/Bl Bl   W/Or Or   W/Gr Gr   W/Br Br
5    4    1    2    3    6    7    8

Cross-over

Normal patch cables are wired straight through, pin 1 to pin1, pin 2 to pin 2 etc. For Ethernet, pair 2 is send and pair 3 receive and this allows computer to be connected to a hub or switch. A cross-over cable reverses the send and receive pairs so that connections computer to computer or switch to switch can be made directly. The plug on one end is wired as follows (coincidentally this is also the T568A pattern)

W/Gr Gr   W/Or Bl   W/Bl Or   W/Br Br
1    2    3    4    5    6    7    8

If you are using (or planning) Gb Ethernet then your cross-over cables will also need to reverse pairs 1 and 4. Cross-over cables are often not needed as much equipment has a cross-over button or a special uplink socket or, now auto-senses and changes over automatically.

W/Gr Gr   W/Or Br   W/Br Or   W/Bl Bl
1    2    3    4    5    6    7    8

Fixed wiring, sockets and patch-panels should never be wired cross-over fashion, it will only confuse people.

Some special use connection patterns

10Mb and 100Mb (fast) Ethernet only uses pairs 2 and 3 (orange and green). Power-over-Ethernet uses pair 1 (blue) as the +ve and pair 4 (brown) as the -ve up to about 13W in the standard wiring configuration. Gb Ethernet uses all four pairs so power-over-Ethernet is not possible with this. No special connections are required.

Analogue telephone over Cat5 uses pairs 1 and 2. I have seen it suggested that a single cable can be split to use two pairs for Ethernet and the other two (pairs 1 and 4) for telephone but I wouldn’t recommend it. Use RJ45 throughout with standard connections and adapters for phone use if required. Pins 2 and 5 (on the telephone plug) are the signal, pin 3 is the bell and pin 4 ground. Pins 1 and 6 exist but are only used for PBX digital lines.

1    2    3    4    5    6    7    8 RJ45
|    |    |    |    |    |    x    x
4    3    6    2    5    1           BT type socket

If you are short of cable outlets then you can get special adaptors to run Ethernet and telephone over the same wire – but they are expensive! Note that, for some unaccountable reason, BT plugs number in reverse order to the sockets.

ISDN connections are the same as for Ethernet but I don’t know what pairs they use.

VGA and Video over Cat5 is now cost effective for those longer runs and requires a matched pair of adapters, often powered at at least one end. Standard wiring connections are used.

Finally one that you won’t come across, but I happen to need—Sun Netra and Cisco Serial console connection (plug), the other end of the patch lead being standard order.

Br   W/Gr Gr   Bl   W/Or W/Bl Or   W/Br
1    2    3    4    5    6    7    8

When you buy equipment these days you can never be sure what power connectors you will need. Disregarding the wall outlet types, which vary in different countries and also bypassing the seemingly hundreds of low voltage connectors designed so that the wart from one supplier won’t fit equipment from another, we still have a problem with AC mains connectors.

Starting at the domestic end of the market, power inlets can be flat two pin with a notch on each side (Figure-of-Eight) rated at 2.5A. These are IEC-60320 type C7/C8. If the equipment is earthed then it will be an Ace-of-Clubs type plug called type C5/C6.

By far the majority of pro-audio and computer equipment has a three pin type commonly called a Euro plug rated at 10A, properly known as type C13/C14. They are common, probably because they are cheap, but do have a habit of falling out if knocked. This is sometimes incorrectly called a kettle plug but that one should have a side notch making it type C15/C16 for high temperature use. They are interchangeable one way round and I have also seen them used in 13A applications (like kettles!).

When you get to the big stuff then there is the similar Euro style plug but with horizontal pins rated at 16A called type C19/C20 (or C21/C22 if bevelled). A more recent addition to the choice is the Neutrik NAC3 Powercon for up to 20A. This is a lovely compact design based on their earlier loudspeaker plugs (which we called hose connectors) with a bayonet fit and latch. Grey ones are outlets, blue ones are inlets and they are not interchangeable.

At the top end, often seen on lighting gear and main power feeds, are what are known as Commando, Caravan or BS4343 plugs, huge blue things with caps on the sockets. The correct name is IEC-60309 and if they are 43mm diameter then they are 16A, if bigger still then they are 32A. These are industrial specification, water resistant and virtually indestructible. They come in other colours and pin numbers for different voltage, frequency and phases but there is no risk of connecting them up wrongly as they don’t mate.

Individual lighting units normally come with the old UK 15A BS 546 round pin plug (you may find some low power ones that have the smaller 5A plug) and it is best to stick with them rather than change them all to the newer 13A square pin because you will find it easier to hire lamps.

Another variety, for which I can’t find a picture, is the Wago plug, used on some UPS and power distribution systems. They have three pins in a line and a latch.

There are a lot of others, for example US two blade plugs and the old Bulgin plugs which, fortunately, are not used on new equipment but you may find them on antique devices.

When you include the panel and inline, male and female, angled and straight and whatever, this is far too many different types. I just wish they could standardise.

An induction loop is a system that allows hearing aid users to receive a signal directly from microphones placed close to the users rather than rely on transmitted sound. It is of considerable benefit to them because it separates out just the sound required and removes other distracting noises and reverberation.

The building regulations (1992) require that new buildings open to the public and ones that are substantially reconstructed are fitted with systems for ticket booths and auditoriums over 100 sq m. Systems must meet BS8300:2002, BS7594:1993 and EN60118-4.

The Disability Discrimination Acts (1995 & 1999) may extend this to existing premises if it is otherwise unreasonably difficult for disabled people to use the facilities. An installed loop must be properly maintained and staff must know how to use it. I have been told that some of these regulations are retrospective and older systems may no longer conform but, apart from this maintenance requirement, I can’t find any evidence for this.

The specification for an induction loop system requires a current drive amplifier (a normal PA amplifier is voltage driven) with a single turn loop and account should be taken of losses caused by building metalwork such as girders and reinforced concrete. The input to the system can be dedicated microphones or from an existing sound system.

Ampetronic, a leading manufacturer in the field, say that the type of wire is not too important so long as it appropriately sized to give a total resistance in the range required by the amplifier. The normal arrangement is for it to run around the listening area. They also say that it should not be at head height, though I haven’t discovered why, but floor level (or ceiling if it is not too high) is more normal.

The recommended field strength is 0.1 A/m for an average level speech signal with peaks at four times that value which allow for some dynamics. Larger variations are flattened out using a compressor built into the amplifier. For a single turn loop, and bypassing all the complex equations and caveats, the peak current can be simplified to approximately 4a/9 where “a” is the length of the shortest side in metres. From this you can calculate the wire gauge and the amplifier power required.

Once installed, the easiest way to measure the field is with a pink noise generator amplified to normal listening levels (though you may want to turn off the loudspeaker amplifier) and measure the field strength with a meter in different places. With a listening device you can also test the tone over the coverage area. The frequency response is required to be flat (+/- 3dB) between 100Hz and 5kHz with an upper response limited to 16kHz. High frequency losses are caused by building metalwork and compensatory EQ (and additional current) will be needed to correct for this. You may need professional advice for particularly large, oddly shaped or difficult buildings.

A hot topic at the moment is Ofcom’s proposal to sell off the Analogue TV frequency bands, called the Digital Dividend. This is controversial, not only for those people who want to retain their old tellies bus also for the live entertainment industry. The reason for this is that digital TV requires less spectrum than analogue so they can free up some bands as the analogue is turned off. However, they currently share these bands with low bandwidth, low power uses such as radio microphones who slip into the gaps between TV transmissions.

How does this affect church systems?

The VHF Band III license exempt range 173.8 to 175.0 MHz is not affected at all. Although the band is coming into use for DAB radio, it misses our channels.

The UHF licence exempt Channel 70 (863.1 to 864.9 MHz) is also to remain unchanged under the proposals.

So no change then! But one other proposal will have an effect. It is proposed to change the currently licensed Channel 69 (854.1 to 861.9 MHz) to become license exempt. This could be good news for churches and other amateur use because those frequencies, which come on many systems but you are not supposed to use, suddenly become available.

As you might expect, professional users who have a considerable investment in licensed equipment are up in arms about this and other changes so I don’t expect the proposal to get through unaltered. Ofcom wants them to go digital at the same time but the technology is not up to it yet.

During the install of our projector system I have been very impressed with the Kramer products. The main component is the Switcher/Scaler which is the heart of the system and the general impression is that they do what they are supposed to do with no fuss and in exactly the way that you would expect. The VP719 is a 7 input, single VGA output device (inputs are VGA, DVI, 2 x composite, 2 x S-Video and component) and it seems to be able to cope with whatever you throw at it without a glitch.

There are inevitably small faults where details off the main function could be thought out a bit better. This is clearly an installation device rather than portable/mobile and as such, some things should be hidden from the end user. In particular, the remote control is much too complex exposing controls that would be rarely required—a very prominent button changes the output resolution—something that is not required after install. If things like this are required on the remote then there should be an “advanced” panel with a cover. On the other hand, there is no “blank” button on the remote at all but there may be a programmable feature to enable this some other way.

In an installation like ours the actual device is hidden away in a rack so we use the computer serial connection with the GUI application to actually control it. This just duplicates the function and appearance of the remote but with the same problems; actually worse because it is a multi-device application for all models so there are lots of redundant controls. It needs to be customisable so that unwanted functions can be removed and, in particular, more meaningful labels put on the input selectors so that you don’t have to remember which device is plugged into which socket.

Another improvement would be a second VGA input. We have worked around the lack of this by using the DVI input for the main control computer but that was not ideal for other reasons and would not always be possible—for instance with two laptops. Perhaps we needed the 724 model but this is somewhat more expensive with a lot of unneeded features.

Now that it is installed the silly audio connections are not a problem but I don’t see why standard RCA (for the video channels) and mini jack (for the computer channels) were not used. XLR for the PA output would have been nice but I can see that there is a space limitation on a 1u box. Does anyone seriously use the 5 Watt audio amplifier built in?

Anyway, notwithstanding these little gripes, I thoroughly recommend this device for any simple church or conference room setup.