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10 metres audio cable going into PC = too long?

Discussion in 'Electrical Engineering' started by Andy, Apr 18, 2006.

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  1. tony sayer

    tony sayer Guest

    Yes but quite some time ago now. FWIW we don't or very rarely have long
    lumps of overhead line anymore that carry baseband audio. For voiceband
    circuits these days its digital end to end with a A/D and D/A convertor
    at each end.

    And for phones its going much the same way, well over here at least.
    BT have the 21CN nets which are data circuits which you run data or
    audio or whatever you like over them..
    I asked a couple of cable jointers who were working beside the road the
    other day re that one, and it seems that its the exception rather than
    the rule these days. There is some cable which has a foil screen around
    it, but as to woven braids seems they aren't used anymore..
    Well the ones ntl use here according to a friend of mine who works with
    their plant day in and day out sez otherwise. Seems only some of the
    cable they use has a foil screen but then again they use fibre and co-ax
    for distances of any length, seems digital rules;)..
    No its not, you have to define what your using it for an in what
    Yes except that if we're talking like we were about currents circulating
    in the "screen" of a multicore cable, then there is going to be quite a
    bit of difference in practice between a heavily woven copper braid and
    the light foil wrap where the connection to that is by a fairly thin
    drain wire...
    Yes we sometimes do, but very rarely these days, it s getting to be a
    very digital world over here. Analogue circuits are quite rare nowadays
    and BT have been known to have to get guys out of retirement to work on
    the few remaining ones!. If you wanted say a speech band 300- 3500 Hz
    point to point circuit these days it'd be digital end to end or if you
    required a music grade circuit that would definitely be digital copper
    would only be for the patch leads to connect the gear.

    Even some recording and sound re-inforcement systems use digital leads
    from the stage area to the mixer now..

    Well they don't define what you are doing with that. Consider say 10
    meters of Andrews LDF 4-50 cable connected to a transmitter with the
    correct plug, what are they connecting that other end to?. Nothing or a
    load partially connected?.

    Or do they mean the connection to the shield, referred to the point
    where that would normally be connected, is greater than one tenth of
    lambda?. If thats what they meant then they didn't describe that very

    It seems that they were thinking of say a braided cable like perhaps
    RG214 or similar when you "could" take that out as a pigtail

    I think its relevant on the subject, but YMMD as they say..

    I'll have a look at that again when I get a moment and try some
    experiments here too...
    Well how far do you want to go with that;?...

    What do you do over there are you involved in a Telco?..
    The above was only to demonstrate what I meant by balanced working..
    As above just for demo..
    Well I have tried that and it doesn't hum at least not what I can hear!.
    And out mains is quite unclean;!..
    Humm... What do you use out there in deepest Alaska, batteries;-?.....
    Yes it is poor circuit design, but people do it all the time!...
  2. tony sayer

    tony sayer Guest

    Do they have engineers anymore?, the accountants that run the industry say
    they don't need 'em!..

    That above example was for a small transmitter that is in a remote location
    that is fed by a long overhead copper pair, well two of them for stereo, and
    that goes into line trannies and equalisers and it didn't have any discernible
    humm on it. However thats about to change, a digital microwave link is to be
    installed as soon as, copper is on its way out it seems!...
  3. tony sayer

    tony sayer Guest

    They seem to do things differently over there Floyd, my friend who works
    for a Telco here reckons that if they get 80 working pairs out of a
    newly installed 100 pair their doing well;!.

    All due to employing subbies who sub out and then sub some more;(.

    He said they didn't measure things like signal to noise ratios and such
    anymore as they don't need to its all going digital anyway and digital
    is perceived as "perfect" so no need!........
  4. Guest

    In most places in the US your POTS line becomes one channel of a
    digital T1 pretty close to your house. A tip is whether a 56kbs modem
    works for you. That is exploiting the 64kbs T1 channel hardware. The
    "last mile" <or less> is usually the only part of POTS that is analog.
    There may still be a number five office somewhere in the US, switching
    analog lines but I am not suure where it would be. Everyone is digital
    at the central office.
  5. No it isn't. The line into my house (and everyone else's house) is
    copper, delivering an analogue voltage to an analogue handset.
  6. Oh look! Little Stewie's discovered that "Digital" can mean two
    different things! Bless!
  7. Nick Gorham

    Nick Gorham Guest

    But to continue being picky, the pairs in a length of CAT5 don't know or
    care if the signal they carry is being called analog or digital, its
    still just a voltage that varies with time. And the "analog" cable from
    the phone co distribution box here carries analog voice, and used to
    carry digital ISDN, and now carries both analog voice and digital ADSL
    at the same time. So what is it, analog or digital, or maybe it doesn't

  8. We're talking about POTS aren't we? It's analogue.
  9. Wrong again. A distribution box distributes. You mean a convertor
  10. Nick Gorham

    Nick Gorham Guest

    Isn't everything when you get to the wire? But the same pair still
    carries digital information.
  11. tony sayer

    tony sayer Guest

    To clarify that..

    BT the main operator in the UK has its exchanges linked together these
    days by Fibre and has done so for many years now. They break the fibre
    down to copper at the exchange, add in loop volts and line break etc for
    older phones, and then route that to the subs premises. However the
    distances aren't that great, around 3 to 4 miles or so in rural areas
    and less in urban ones. Using a multipair but what also might make some
    difference between UK and US practice is that this will invariably be
    underground plant in their own ducts. An overhead multipair cable is
    quite rare, and is likely to be of a lowish number of pairs and not that
    long probably only from a distribution pole to a group of subs not that
    far away, i.e. a few hundred meters.

    The Cable co's in the UK, firms like Comcast and Bellcable etc are now
    all rolled up into the ntl and Telewest outfit, soon to be renamed
    again!. They use a similar practice but the distance issue is changed
    again. They will have roadside cabinets instead of exchange office type
    buildings, (though they will have a central switch building) that breaks
    the fibre down using Nokia equipment's to copper to the subs premises.
    However once again these all are underground ducted cables but the
    distances there are more likely to be of a few hundreds of yards!.

    We don't have this sort of arrangement over here;!...

    In fact I've never seen a phone cable tacked to a power pole carrying
    more than 240 volts!. And for that the cables are spece'd differently.
    To have phone and comms cables with power lines at the sort of voltages
    described on those poles just isn't done here!. The health and safety
    police just don't allow!! apart from that there is an aversion to
    overhead plant in the UK most all telecom power services is

    Yes as above. However the market for bizz and residential telephony
    services is rapidly changing in the UK . Mobile use is now very high and
    climbing. In fact a lot of young people won't have a landline phone.
    They see it that a mobile is a "must have" and for around 30 or so
    pounds a month you can get around 500 minutes a month inclusive calls.
    Very cheap rates are applied at evenings and weekends.

    The extra monthly cost of a phone line can buy quite a bit more call
    capacity, and the mobility issue a cheap and easy to use text service
    landlines are finding it hard to compete!.

    BT 's 21st century programme is to do away with their circuit switched
    networks and make it all IP based packet switched. A lot of people use
    such services as Skype and other phone over the net services. The only
    thing some people have a phone line in for is for broadband provision!..
    However these can and are supplied over radio based nets as well as via
    UMTS services.

    Well it might be over there with all that overhead distribution but it
    'taint here!. ADSL is very robust and I've never known a problem with
    it. And as they use fibre a lot for phone lines between exchanges, not a
    Not quite so. One of these guys was quite old and very experienced, and
    could recall the days of lead covered cable where they had to do wiped
    joints etc. So don't despise the benefit of experience. Those guys have
    probably seem more cable close up than you'll ever likely too!.

    Course they don't specify it, but some old BT "Poles and holes" staff do
    know a lot more that you'd give 'em credit for!..
    If that makes you feel better, and in someway superior, so be it..
    you're welcome;)
    Well it seems it isn't always the case here.
    As above their use of multipair isn't that great. Its underground and
    all in cable only ducts. They don't even run mains in there they source
    that off street lightning cabs..
    Once again if its circulating currents in a cable screen as per the
    original discussion, then for a given diameter of cable there will be a
    difference between the current that can flow in that a braided multicore
    will carry more current than one with a ally wrap and small drain wire..
    Nope. I don't work for a phone company like you do, but I do have to
    have a very good working know how of telecoms, phone, appl, private
    circuit, voice band and wider-band, and ISDN and data..
    Nope. Sorry but the "phone engineer" as we know is a vanishing breed:!.

    Give you an example. We installed a PABX system for a radio station
    recently. Its all based on a PC and uses SIP phones. Most all the
    outgoing calls are over a GSM gateway to other mobiles 70% of calls, and
    inter office calls are via ADSL. Probably 15 % are carried over the ISDN
    circuits connecting it to BT. It is now no longer a phone provider
    service contract issue its an IT one now!..
    Actually read that through again;) It isn't that wonderfully written for
    what they want to convey. I've mailed that off to a few other people to
    see what they "visualise" that cable to be doing in that description!..
    Yes I design and install aerials thanks.

    Antenna's are what insects have;)
    Yummie. Biccy's is what we call 'em here, dunk 'em in your tea
    traditionally best stirred with a screwdriver:))
    OK on that then..
    I've been in TV transmission, Radio broadcasting, studio design and
    maintenance, data comms, and two way radio......among others...
    Indeed it does.

    Now what was the original argument again;?.....
  12. tony sayer

    tony sayer Guest

    Errmm... No he's not an engineer. They don't have "them" anymore;-(.
    You may not know it but most UK industry is run by accountants these
    days. Once the mighty BBC had an engineering director.. they don't
    nowadays. They have bullshit speak mongers. Engineers are shat on from a
    great height, and are treated like dirt, thats why a lot went over
    there, brain drain we called it;(.

    No self respecting UK parent who wanted their son or daughter to do well
    would have them do engineering. Law, Accountancy, medicine or the civil
    service are all the "Professions". Engineers?, no way!..

    No the one I'm referring to is a technician who does know their system
    inside out, and is very good at what he does but he won't be there next
    round of redundancies and job cuts, as the management don't think they
    need him!.

    You haven't seen what some of the subbies get up to. Suppose over there
    you have your own in house people.

    They don't do that here;((
    Yes they do have such go-nogo devices...
    Humm... Over there?.. Over here?.....
  13. Poor taste, yes. Retard, no.

    Just politically incorrect and proud of it.

    Two Muslim women in Millets trying on rucksacks - one says to the other
    "does my bomb look big in this?"

    Difference between Basil Brush and a Muslim? A Muslim only goes boom once.

    etc etc...
  14. Not here it isn't. The main voice line coming into the building is ISDN.

    The fax line is analogue though (and is the one that carries the ADSL
    broadband as well).
  15. Note that POTS is the topic under discussion.
  16. HTH
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