[CQ-Contest] Network cables

[Bill Coleman]

On 10/4/01 6:08 PM, andrew at andrew at gi0nwg.freeserve.co.uk wrote:

>
>>Typically, it isn't the computer that dies, but the CONNECTIONS 
>>surrounding the BNC T connector. I've seen lots of 10Base2 networks that 
>>were really flaky. 
>
>Quality BNC connections are fine in a network if you are not constantly
>moving things around.  Probably the worst to use are those dreaded crimp
>connections.  I'm not at all surprised that they fail regularly!

Proper crimp connections shouldn't fail any more than proper soldered 
connections. Unfortuanately, getting proper connections is hard.

The point is -- in 10Base2, a failure of one connection can bring the 
whole network down. In IT departments where such networks are used, they 
usually have special reflectometry tools in order to locate such breaks. 
They happen frequently enough to warrant them.

>>10BaseT or 100BaseT works a lot better. Plus, you 
>>don't need to worry about proper termination.
>
>I wouldn't say 10BaseT works any better than 10Base2, they both run at
>10Mb/s and I would consider both to be equally reliable.

Yes, 10BaseT and 10Base2 are identically the same speed. However, I 
wouldn't characterise them as having the same reliability.

>Naturally,
>100BaseT will work better at 100Mb/s but most hams don't need that sort
>of speed (a 10Mb/s easily runs a four computer gaming network so should
>easily run a multi-computer contesting network).  However, with UTP
>networks you need extra equipment (hubs) unless you are only connecting
>two computers when you can use a cross-over lead.

Hubs are relatively cheap. You'd end up spending about as much on a hub 
as you would on the equivalent number of BNC T connectors. I'll agree 
that 10/100 hubs are more expensive. 

>>UTP is much easier to wire, 
>
>I think it's debatable whether UTP is easier to wire.

UTP has three advantages:
1) the cable is smaller, lighter and more flexible than coax, which makes 
it easier to run.
2) the cable is less susceptable to damage. Crimp coax too much with a 
cable staple, and you have to replace the whole run or make a splice.
3) the cable is a whole lot cheaper than coax, even for cat 5.

>All cables have
>to go to a central point (the hub) and if the computers are well spaced
>(as could be the case in a contest network) things start to get tricky.

The central point also allows for more flexibility. With coax, since the 
run is daisy-chained, if you want to move a computer a couple of feet 
left or right, you may not have enough cable. Running everything to a 
central point makes that easier.

However, UTP isn't restricted to central point wiring. If you have a 
cluster of machines, you can use a hub (remember, they are cheap) to 
avoid having to wire back to the central point for every machine in the 
cluster. On my desk at work, I have a mini-Hub that services two desktop 
machines and a couple of laptops from one drop.

>You also have to buy the cables unless you have the special tools to put
>the UTP ends on the cable.  Most hams have some RG58 and a soldering
>iron and maybe even a couple of BNC connectors and can easily build that
>themselves.

The patch cables are available cheaply from a large number of sources. 
(Although it took me a while to find a crossover cable) I bought a bunch 
from Home Depot this last year.

IDC RG-45 jacks are readily available. You don't have to install RJ-45 
plugs if you wire every run to a jack -- so no special tools are needed.

>>and apparently has a great deal of rejection of common-mode RF 
>>currents.
>
>Properly installed coax or UTP networks should not have a problem with
>RFI at amateur power levels (I've never had a problem with coax based
>networks).  That's assuming proper installation procedures have been
>used to keep RF in the shack to a sensible level.  That should be
>standard operating practice anyway.

Yes, I agree. The main fear hams have with UTP is that it might cause or 
be subsceptable to RFI. 

The bottom line is that UTP is commonly used in businesses, and this type 
of equipment is widely available at low prices. 10Base2 is being phased 
out, so it's harder to find, and there's no upgrade path to 100 Mb.



Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901


--
CQ-Contest on WWW: http://lists.contesting.com/_cq-contest/
Administrative requests: cq-contest-REQUEST at contesting.com