Sharing broadband across half mile

Archived from groups: alt.internet.wireless (More info?)

I want to share my broadband connection with a friend who lives about
half a mile away.

I was hoping I could do this by installing antennas in both our lofts
and connecting it to a wireless access point connected to my Telewest
cable modem. There is a raised railway embankment between our two
locations, so direct line of sight is not possible. Is this a problem?

Can anyone tell me if this is a feasible option. Also, any
tips/websites where I can build the kit cheaply.
21 answers Last reply
More about sharing broadband half mile
  1. Archived from groups: alt.internet.wireless (More info?)

    Dave D wrote:
    > I want to share my broadband connection with a friend who lives about
    > half a mile away.
    >
    > I was hoping I could do this by installing antennas in both our lofts
    > and connecting it to a wireless access point connected to my Telewest
    > cable modem. There is a raised railway embankment between our two
    > locations, so direct line of sight is not possible. Is this a problem?
    >
    > Can anyone tell me if this is a feasible option. Also, any
    > tips/websites where I can build the kit cheaply.

    You can buy ethernet cable for pretty cheap, but about every 1,000 feet
    or so you need to use a hub (repeater).

    Seriously, sometimes non-line-of-sight works when it isn't supposed to.
    The only way you'll know is to try it.
  2. Archived from groups: alt.internet.wireless (More info?)

    Dave D <frank.praverman@bigfoot.com> wrote in
    news:ro0sd0dm1373tgjlv9k47v1utf03vj2204@4ax.com:

    > There is a raised railway embankment between our two
    > locations, so direct line of sight is not possible. Is this a problem?

    If you are using a directional antenna with a focused beam pattern it will
    likely cause a problem. Can you get your antennas any higher?

    --
    Lucas Tam (REMOVEnntp@rogers.com)
    Please delete "REMOVE" from the e-mail address when replying.
    http://members.ebay.com/aboutme/coolspot18/
  3. Archived from groups: alt.internet.wireless (More info?)

    On Sun, 27 Jun 2004 00:18:20 +0100, Dave D
    <frank.praverman@bigfoot.com> wrote:

    >Also, any
    >tips/websites where I can build the kit cheaply.

    http://www.freeantennas.com
    http://www.saunalahti.fi/%7Eelepal/antennie.html
    http://www.seattlewireless.net/index.cgi/DirectionalAntenna
    http://www.seattlewireless.net/index.cgi/DirectionalParabolic
    http://www.qsl.net/k3tz/ (2.4GHz patch antenna)
    http://flakey.info/antenna/biquad/
    http://flakey.info/antenna/omni/quarter/ (don't)


    --
    Jeff Liebermann jeffl@comix.santa-cruz.ca.us
    150 Felker St #D 831-336-2558
    Santa Cruz CA 95060 AE6KS
  4. Archived from groups: alt.internet.wireless (More info?)

    > cable modem. There is a raised railway embankment between our two
    > locations, so direct line of sight is not possible. Is this a problem?

    Chances are that it's a non starter as a direct link but there's another
    way. This is what we had to do:-

    www.nodomainname.co.uk/Equation/equation_broadband.htm

    In other words, you'll either have to over or around.

    > Can anyone tell me if this is a feasible option. Also, any
    > tips/websites where I can build the kit cheaply.

    www.nodomainname.co.uk/cantenna/cantenna.htm

    David.
  5. Archived from groups: alt.internet.wireless (More info?)

    In article <G_udncMcTa5l00PdRVn-sw@pghconnect.com>,
    =?ISO-8859-1?Q?R=F4g=EAr?= <abuse@your.isp.com> wrote:
    :You can buy ethernet cable for pretty cheap, but about every 1,000 feet
    :or so you need to use a hub (repeater).

    Which ethernet standard were you thinking of, that would support
    such long distances between repeaters? 10BaseTX, 100BaseT, 1000BaseT
    are limited to 100 meters per segment. One of the older standards
    (5Base2 or something like that) allows 220 meters per segment.
    But I do not recall any standard that allows one to approach 300 meters ?
    --
    WW{Backus,Church,Dijkstra,Knuth,Hollerith,Turing,vonNeumann}D ?
  6. Archived from groups: alt.internet.wireless (More info?)

    On 27 Jun 2004 14:33:29 GMT, roberson@ibd.nrc-cnrc.gc.ca (Walter
    Roberson) wrote:

    >In article <G_udncMcTa5l00PdRVn-sw@pghconnect.com>,
    >=?ISO-8859-1?Q?R=F4g=EAr?= <abuse@your.isp.com> wrote:
    >:You can buy ethernet cable for pretty cheap, but about every 1,000 feet
    >:or so you need to use a hub (repeater).

    >Which ethernet standard were you thinking of, that would support
    >such long distances between repeaters? 10BaseTX, 100BaseT, 1000BaseT
    >are limited to 100 meters per segment. One of the older standards
    >(5Base2 or something like that) allows 220 meters per segment.
    >But I do not recall any standard that allows one to approach 300 meters ?

    Standards are made to be conservative and following them is a good
    assurance that things will work under all circumstances and
    environments. Standards do not consist of a brick wall limit, where
    everything falls apart if slightly exceeded. The trick is to know
    just how conservative they are, and what controls the real limits. As
    always, breaking standards are risky, educational, offers a few
    suprises, is lots of fun, and must be tested thoroughly.

    I have installed wired network links running well beyond the various
    specifications. For example, I have a 10base2 coax cable network
    running on RG-6/u (CATV coax) at 1200ft. No problems or errors. Note
    that there are commerical products that also do this:
    http://www.multilet.com/us/baseband/product_range/product_range.htm

    I routinely test 1000ft rolls of CAT5 cable by crimping connectors on
    both ends and connecting them to a switch and laptop. No problems at
    10baseT speeds, but not a great idea at 100baseTX. We had a
    neighborhood wired ethernet system running 7 houses with about 500ft
    of CAT5 daisy chained between houses. End to end was about 3000ft.
    We tried to follow the 5-4-3 rule, but the topology was not very
    helpful. I used switches instead of hubs (repeaters) and all was
    well.

    I've also used existing 25pair telco cable bundle at 600ft for
    10baseT.

    There are a bunch of other tricks to using overly long wiring
    segments, and understanding their limitations, but since this is a
    wireless newsgroup, methinks I'll avoid the inevitable flame war and
    leave out the details.


    --
    Jeff Liebermann jeffl@comix.santa-cruz.ca.us
    150 Felker St #D 831-336-2558
    Santa Cruz CA 95060 AE6KS
  7. Archived from groups: alt.internet.wireless (More info?)

    > But I do not recall any standard that allows one to approach 300 meters ?

    No but we used to run our thin ethernet segments to 430m before they'd
    fall over but then:-

    a) The NIC's were manufactured by the company I worked for and they had
    a special 300m mode (although most weren't set to run with that)

    b) We were the tech support department

    c) Had a time domain reflectometer to measure it when it all stopped

    :)

    David.
  8. Archived from groups: alt.internet.wireless (More info?)

    "David Taylor" <djtaylor@bigfoot.com> wrote in message
    news:MPG.1b48ec5c6092976e989c8e@news.individual.de...
    > > But I do not recall any standard that allows one to approach 300 meters
    ?
    >

    a thick ethernet segment (10Base5) is good for 500m - but this is thick
    expensive co-ax, and you need separate transcievers.

    > No but we used to run our thin ethernet segments to 430m before they'd
    > fall over but then:-
    >
    > a) The NIC's were manufactured by the company I worked for and they had
    > a special 300m mode (although most weren't set to run with that)

    3com - their NIC cards for thin ethernet were certified to 300m
    >
    > b) We were the tech support department
    >
    > c) Had a time domain reflectometer to measure it when it all stopped
    >
    > :)
    >
    > David.
    --
    Regards

    Stephen Hope - return address needs fewer xxs
  9. Archived from groups: alt.internet.wireless (More info?)

    "Walter Roberson" <roberson@ibd.nrc-cnrc.gc.ca> schreef in bericht
    news:cbmlrp$80n$1@canopus.cc.umanitoba.ca...
    > In article <G_udncMcTa5l00PdRVn-sw@pghconnect.com>,
    > =?ISO-8859-1?Q?R=F4g=EAr?= <abuse@your.isp.com> wrote:
    > :You can buy ethernet cable for pretty cheap, but about every 1,000 feet
    > :or so you need to use a hub (repeater).
    >
    > Which ethernet standard were you thinking of, that would support
    > such long distances between repeaters? 10BaseTX, 100BaseT, 1000BaseT
    > are limited to 100 meters per segment. One of the older standards
    > (5Base2 or something like that) allows 220 meters per segment.
    > But I do not recall any standard that allows one to approach 300 meters ?

    10BASE5 runs up to 500 meters.
    10BASE2 is certified to 195 meters.
    Early fiber segments as far as 3500 meters.
  10. Archived from groups: alt.internet.wireless (More info?)

    "David Taylor" <djtaylor@bigfoot.com> schreef in bericht
    news:MPG.1b48ec5c6092976e989c8e@news.individual.de...
    > > But I do not recall any standard that allows one to approach 300 meters
    ?
    >
    > No but we used to run our thin ethernet segments to 430m before they'd
    > fall over but then:-
    >
    > a) The NIC's were manufactured by the company I worked for and they had
    > a special 300m mode (although most weren't set to run with that)
    >
    > b) We were the tech support department
    >
    > c) Had a time domain reflectometer to measure it when it all stopped
    >
    > :)
    >
    > David.

    195 m for 10base2 was rather restrictive. If you knew what you were doing
    (i.e.
    use good quality cables, connectors and terminators) then it is not to
    difficult
    to calculate the maximum possible cable length. Having a TDR does help :-)
    A TDR used to be pretty expensive around 1985, how are prices these days?

    Hans
  11. Archived from groups: alt.internet.wireless (More info?)

    "Jeff Liebermann" <jeffl@comix.santa-cruz.ca.us> schreef in bericht
    news:5uotd0hfdeqsdmmgih4got8i9ook1lde3m@4ax.com...
    > On 27 Jun 2004 14:33:29 GMT, roberson@ibd.nrc-cnrc.gc.ca (Walter
    > Roberson) wrote:
    >
    > >In article <G_udncMcTa5l00PdRVn-sw@pghconnect.com>,
    > >=?ISO-8859-1?Q?R=F4g=EAr?= <abuse@your.isp.com> wrote:
    > >:You can buy ethernet cable for pretty cheap, but about every 1,000 feet
    > >:or so you need to use a hub (repeater).
    >
    > >Which ethernet standard were you thinking of, that would support
    > >such long distances between repeaters? 10BaseTX, 100BaseT, 1000BaseT
    > >are limited to 100 meters per segment. One of the older standards
    > >(5Base2 or something like that) allows 220 meters per segment.
    > >But I do not recall any standard that allows one to approach 300 meters ?
    >
    > Standards are made to be conservative and following them is a good
    > assurance that things will work under all circumstances and
    > environments. Standards do not consist of a brick wall limit, where
    > everything falls apart if slightly exceeded. The trick is to know
    > just how conservative they are, and what controls the real limits. As
    > always, breaking standards are risky, educational, offers a few
    > suprises, is lots of fun, and must be tested thoroughly.
    >
    > I have installed wired network links running well beyond the various
    > specifications. For example, I have a 10base2 coax cable network
    > running on RG-6/u (CATV coax) at 1200ft. No problems or errors. Note
    > that there are commerical products that also do this:
    > http://www.multilet.com/us/baseband/product_range/product_range.htm
    >
    > I routinely test 1000ft rolls of CAT5 cable by crimping connectors on
    > both ends and connecting them to a switch and laptop. No problems at
    > 10baseT speeds, but not a great idea at 100baseTX. We had a
    > neighborhood wired ethernet system running 7 houses with about 500ft
    > of CAT5 daisy chained between houses. End to end was about 3000ft.
    > We tried to follow the 5-4-3 rule, but the topology was not very
    > helpful. I used switches instead of hubs (repeaters) and all was
    > well.
    >
    > I've also used existing 25pair telco cable bundle at 600ft for
    > 10baseT.
    >
    > There are a bunch of other tricks to using overly long wiring
    > segments, and understanding their limitations, but since this is a
    > wireless newsgroup, methinks I'll avoid the inevitable flame war and
    > leave out the details.
    >
    Jeff, a little theory does not harm anybody. Wired or wireless, technology
    obeys the laws of physics, right?
    Hans
  12. Archived from groups: alt.internet.wireless (More info?)

    On Sun, 27 Jun 2004 20:55:26 +0200, "Hans Vlems"
    <hvlems.dotweg@zonnet.nl> wrote:

    >> There are a bunch of other tricks to using overly long wiring
    >> segments, and understanding their limitations, but since this is a
    >> wireless newsgroup, methinks I'll avoid the inevitable flame war and
    >> leave out the details.

    >Jeff, a little theory does not harm anybody. Wired or wireless, technology
    >obeys the laws of physics, right?
    >Hans

    Ok, I have an audience. Good excuse to not do the laundry.

    First, skim through the ethernet FAQ at:
    http://www.faqs.org/faqs/LANs/ethernet-faq/
    There's quite a bit in there on standards and calcs.

    The big headaches are NEXT (near end crosstalk) and line loss. While
    this is mostly a function of the CAT5 cable, it's also seriously
    affected by the sensitivity of specific switches and ethernet cards.
    I gotta dig through my notes for the exact numbers. Maybe later.

    In general, FDX (full-duplex) vs HDX (half-duplex) is a compromise.
    FDX removes collision issues from the problem, but is affected by NEXT
    because it simultaneously transmits and receives. Forget about using
    hubs, which cannot do FDX. For very long end to end runs (1000
    meters) through multiple switches, collision timing is the major issue
    and therefore should use FDX. For shorter single runs of about 300
    meters, cable loss and NEXT are the issues. Therefore HDX should be
    used.

    Late collisions are a problem. This is where the 32 bit jam signal
    arrives after the first 512 bits of an ethernet frame. For CAT5, with
    a velocity factory of 0.59, the speed of propogation is 177,000 km/sec
    (300,000km/sec * 0.59). At 10mbits/sec, one bit = 17.7 meters.
    512bits of the header results in a 9000 meters ( 512 * 17.7) limit for
    late collisions. Delays through the switches are not an issue because
    both the original packet and the jam signal are delayed identically.

    For coax, there are two solutions. One is to use a twisted pair to
    coax balun (xformer) and the 10baseT collision detection mechanism as
    in:
    http://www.multilet.com/us/baseband/product_range/product_range.htm
    The velocity factor is 0.65 which results in a slightly longer limit
    of 10,000 meters.

    Another coax solution is to use 10base2 (cheapernet), which uses a DC
    level shift for collision detection. The official end-to-end maximum
    is 1000 meters which methink is rather conservative. The correct
    cable is 50 ohm RG-58/u. However, I've been using RG-6/u 75 ohm coax.
    In theory, there would be substantial reflection problems with voltage
    nulls and peaks along the coax. Therefore, it only works on
    relatively long runs (>100 meters) where the reflected signal is
    sufficiently attenuated to be insignificant. I only use end-to-end
    runs of RG-6/u with no "tee" connectors for additional machines in
    between. Therefore the topology is a star, not the more cenventional
    bus. For interface, I prefer 10baseT to 10base2 converters, but will
    use an old ISA 10baseT ethernet card if desperate.

    There are a few more complications, but I gotta get back to the
    laundry.

    --
    Jeff Liebermann jeffl@comix.santa-cruz.ca.us
    150 Felker St #D 831-336-2558
    Santa Cruz CA 95060 AE6KS
  13. Archived from groups: alt.internet.wireless (More info?)

    "Jeff Liebermann" <jeffl@comix.santa-cruz.ca.us> schreef in bericht
    news:v27ud0pveqfnlcgemnfgqs9n792naa1bd8@4ax.com...
    > On Sun, 27 Jun 2004 20:55:26 +0200, "Hans Vlems"
    > <hvlems.dotweg@zonnet.nl> wrote:
    >
    > >> There are a bunch of other tricks to using overly long wiring
    > >> segments, and understanding their limitations, but since this is a
    > >> wireless newsgroup, methinks I'll avoid the inevitable flame war and
    > >> leave out the details.
    >
    > >Jeff, a little theory does not harm anybody. Wired or wireless,
    technology
    > >obeys the laws of physics, right?
    > >Hans
    >
    > Ok, I have an audience. Good excuse to not do the laundry.
    >
    > First, skim through the ethernet FAQ at:
    > http://www.faqs.org/faqs/LANs/ethernet-faq/
    > There's quite a bit in there on standards and calcs.
    >
    > The big headaches are NEXT (near end crosstalk) and line loss. While
    > this is mostly a function of the CAT5 cable, it's also seriously
    > affected by the sensitivity of specific switches and ethernet cards.
    > I gotta dig through my notes for the exact numbers. Maybe later.
    >
    > In general, FDX (full-duplex) vs HDX (half-duplex) is a compromise.
    > FDX removes collision issues from the problem, but is affected by NEXT
    > because it simultaneously transmits and receives. Forget about using
    > hubs, which cannot do FDX. For very long end to end runs (1000
    > meters) through multiple switches, collision timing is the major issue
    > and therefore should use FDX. For shorter single runs of about 300
    > meters, cable loss and NEXT are the issues. Therefore HDX should be
    > used.
    >
    > Late collisions are a problem. This is where the 32 bit jam signal
    > arrives after the first 512 bits of an ethernet frame. For CAT5, with
    > a velocity factory of 0.59, the speed of propogation is 177,000 km/sec
    > (300,000km/sec * 0.59). At 10mbits/sec, one bit = 17.7 meters.
    > 512bits of the header results in a 9000 meters ( 512 * 17.7) limit for
    > late collisions. Delays through the switches are not an issue because
    > both the original packet and the jam signal are delayed identically.
    >
    > For coax, there are two solutions. One is to use a twisted pair to
    > coax balun (xformer) and the 10baseT collision detection mechanism as
    > in:
    > http://www.multilet.com/us/baseband/product_range/product_range.htm
    > The velocity factor is 0.65 which results in a slightly longer limit
    > of 10,000 meters.
    >
    > Another coax solution is to use 10base2 (cheapernet), which uses a DC
    > level shift for collision detection. The official end-to-end maximum
    > is 1000 meters which methink is rather conservative. The correct
    > cable is 50 ohm RG-58/u. However, I've been using RG-6/u 75 ohm coax.
    > In theory, there would be substantial reflection problems with voltage
    > nulls and peaks along the coax. Therefore, it only works on
    > relatively long runs (>100 meters) where the reflected signal is
    > sufficiently attenuated to be insignificant. I only use end-to-end
    > runs of RG-6/u with no "tee" connectors for additional machines in
    > between. Therefore the topology is a star, not the more cenventional
    > bus. For interface, I prefer 10baseT to 10base2 converters, but will
    > use an old ISA 10baseT ethernet card if desperate.
    >
    > There are a few more complications, but I gotta get back to the
    > laundry.
    >
    Well, you've got the laundry and here it's nearly midnight, so just a short
    comment
    on impedance. 10base2 uses 50 ohms coax, and on a site I used to work at an
    electrical engineer wired up his own office with RG61 (91 ohm impedance).
    We used repeaters then (DEC's multiport repeaters) and all other segments
    connected
    to that same repeater started to have problems.
    The question is: can you get away with non-standard coax provided it is the
    only type
    you use?
    Even then, connecting 50 ohm gear to a cable plant with a different
    impedance is just
    asking for problems. Network load is important too, lightly used LAN's can
    get away
    with cutting some corners.
  14. Archived from groups: alt.internet.wireless (More info?)

    On Sun, 27 Jun 2004 23:37:30 +0200, "Hans Vlems"
    <hvlems.dotweg@zonnet.nl> wrote:

    >> Late collisions are a problem. This is where the 32 bit jam signal
    >> arrives after the first 512 bits of an ethernet frame. For CAT5, with
    >> a velocity factory of 0.59, the speed of propogation is 177,000 km/sec
    >> (300,000km/sec * 0.59). At 10mbits/sec, one bit = 17.7 meters.
    >> 512bits of the header results in a 9000 meters ( 512 * 17.7) limit for
    >> late collisions. Delays through the switches are not an issue because
    >> both the original packet and the jam signal are delayed identically.

    My last line is more than a little bit incoherent. What I meant to
    mumble was that a late collision will cause a switch to propogate a
    corrupted packet through the switch. Jam packets and packets
    corrupted by the jam signal normally do NOT go through a switch.
    (They do go through a repeater/hub). However, if the jam packet is
    late by 64 bytes (header), the switch will merrily pass the following
    data frame even if was intentionally trashed by the jam signal. This
    is why it is a good idea to limit collision domains with switches.

    >Well, you've got the laundry and here it's nearly midnight, so just a short
    >comment
    >on impedance.

    I change my mind. It was about 1PM here and I grab lunch and catch up
    on my magazine reading pile.

    >> Another coax solution is to use 10base2 (cheapernet), which uses a DC
    >> level shift for collision detection. The official end-to-end maximum
    >> is 1000 meters which methink is rather conservative. The correct
    >> cable is 50 ohm RG-58/u. However, I've been using RG-6/u 75 ohm coax.

    Argh. I forgot to mention that you must use 50 ohm terminators, not
    75 ohm. The DC levels used by the 10base2 collision avoidance
    mechanism uses the terminator as part of a voltage divider. (Well,
    it's actually a current source driving a fixed 50 ohm load). If you
    use 75 ohm terminators, the transceiver will think it's permanently
    busy.

    >10base2 uses 50 ohms coax, and on a site I used to work at an
    >electrical engineer wired up his own office with RG61 (91 ohm impedance).
    >We used repeaters then (DEC's multiport repeaters) and all other segments
    >connected
    >to that same repeater started to have problems.

    That's considerably different from running long lengths of RG-6/u.

    I think you mean RG-62 which is 93 ohm coax normally used for Arcnet.
    To the best of my limited experience, DEC never made an Arcnet
    repeater (hub) so my guess is that it was either DECnet or ethernet.
    I don't think it will work. My guess(tm) what may have gone wrong.

    1. 93 ohms is a 2:1 VSWR from the nominal 50 ohms. That's a bit
    much. That will create standing waves (voltage peaks and nulls) along
    the length. A bad choice of cable length and the end points could
    have ended up in a null resulting in no signal delivered.
    2. For short lengths and 2:1 VSWR there's going to be a substantial
    reflected signal, which will interfere with data transmission. If the
    length of the coax segments were considerablly longer, the line
    attenuation would absorb most of the reflections.
    3. 93 ohm coax is rather lossy.
    4. Hopefully, he terminated each segment with a 50 ohm terminator,
    not a 93 ohm arcnet terminator.

    Without knowning the specific topology and lengths, it's difficult to
    speculate beyond the obvious potential problems. 75 ohm to 50 ohm is
    only a 1.5:1 VSWR, which is tolerable. 93 ohm to 50 ohm is about 2:1
    VSWR, which methinks is too much.

    >The question is: can you get away with non-standard coax provided it is the
    >only type you use?

    I think you're asking can you mix different types and impedances of
    coax. Sure, as long as they are the same impedance on a given
    segment. I would not mix coax impedances on a given segement. Of
    course different ports (segments) on a switch can be different.

    >Even then, connecting 50 ohm gear to a cable plant with a different
    >impedance is just
    >asking for problems. Network load is important too, lightly used LAN's can
    >get away
    >with cutting some corners.

    Two of my RG-6/u installs were at a tv production studio and a
    broadcast studio. The network was carrying digitized video traffic,
    spots from the satellite feed, streaming content, giant bloated files,
    and a VoIP intercom. This was not a lightly used network. There were
    two seperate networks in each building. One for user traffic and one
    for server to server replication and backup. I used RG-6/u coax
    because there was plenty of it in the cable trays and a fiber upgrade
    was allegedly planned. They were suppose to be temporary, but ran
    without incident for about 4 years. Two other TV stations and studios
    learned of my method and implimented similar temporary solutions.
    Incidentally, I monitor both of them remotely with various SNMP tools
    and generate MRTG graphs of key traffic statistics and errors. Both
    had successfully saturated the LAN at times, but SNMP showed minimal
    errors at the central ethernet switch.

    Hmmm... laundry. Never mind.

    --
    Jeff Liebermann jeffl@comix.santa-cruz.ca.us
    150 Felker St #D 831-336-2558
    Santa Cruz CA 95060 AE6KS
  15. Archived from groups: alt.internet.wireless (More info?)

    > 3com - their NIC cards for thin ethernet were certified to 300m

    No it wasn't 3com but either way it's like anything, the standard is
    there for a reason, go outside it and you're out of bounds and on your
    own.

    It used to amuse me the conversations that we had with customers who'd
    ask "but will it work if I go another 10 metres?"

    Stock answer "It will be outside spec." We weren't prepared to endorse
    out of spec networks whether they worked or not.

    David.
  16. Archived from groups: alt.internet.wireless (More info?)

    Jeff, you haven't mentioned the electrical effects of increasing line
    lenght by increasing resistance and capacitance either yet.

    Increasing these causes the rising voltage to equate to Ve(-t/CR) and
    decaying voltage of V(1-e(-t/CR)) and so instead of nicely ramped
    waveforms you end up with exponential curves that drag out over time and
    may fail to trigger the threshold voltage of the receiver.

    David.
  17. Archived from groups: alt.internet.wireless (More info?)

    > use good quality cables, connectors and terminators) then it is not to

    :-) Good quality? You should have seen some of the shite attempts at
    making cables by junior tech support staff!

    > to calculate the maximum possible cable length. Having a TDR does help :-)
    > A TDR used to be pretty expensive around 1985, how are prices these days?

    Dunno, pretty cheap these days I'd have though give the processing
    advances. We had a couple, one was a rather large instrument about
    twice the size of a current laptop and interfaced with other instruments
    and the other was basically a "cable tester" but still did the TDR
    function in order to calculate distance to fault.

    David.
  18. Archived from groups: alt.internet.wireless (More info?)

    On Tue, 29 Jun 2004 22:17:28 +0100, David Taylor
    <djtaylor@bigfoot.com> wrote:

    >Jeff, you haven't mentioned the electrical effects of increasing line
    >lenght by increasing resistance and capacitance either yet.

    CAT5 and coax look like a distributed LC network also known as a
    transmission line. Attenuation follows the typical 3dB per octave
    (10dB/decade) rolloff curve. Actually attenuation depends mostly on
    the loss tangent of the dielectric. 10Mbits/sec needs at least the
    3rd harmonic to be properly decoded. That means 30-50MHz of -3dB
    bandwidth is usually sufficient depending upon the sensitivity of the
    ethernet receiver. While dielectric losses are directly proportional
    to the frequency, resistive losses are proportional to the square root
    of the frequency, making resistive effects less signifigant.

    >Increasing these causes the rising voltage to equate to Ve(-t/CR) and
    >decaying voltage of V(1-e(-t/CR)) and so instead of nicely ramped
    >waveforms you end up with exponential curves that drag out over time and
    >may fail to trigger the threshold voltage of the receiver.
    >
    >David.

    Ethernet waveforms are suppose to square waves, not ramps, although an
    ugly triangular waveform is what usually comes out of a bandwidth
    limited coax cable. Should be a photo around somewhere...
    http://www.bitzenbytes.com/101/n115-an-442.pdf
    See figure 5. I've seen far worse come out of a very long piece of
    coax and still get decoded.

    At 300 meters RG-6/u has a loss of:
    MHz Loss (-dB)
    1 2.5
    10 8.5
    30 15.
    50 20.
    I gotta check my overpriced printed copy of the ANSI/TIA/EIA-568-B.2
    (addendum 1) specs to see what propogation delays, delay skewing, and
    insertion loss can be officially tolerated. I suspect that 300 meters
    is well over the loss spec and only the conservative design of the
    transcievers and conservative cable specifications is what allows it
    to work. With -10dB loss at 10Mhz

    Hmmm... I found a partial reference to allowable skewing for EIA-568A:
    "Cable delay skew shall not exceed 45ns/100m between 1 MHz and the
    highest frequency in any specified category." At 10Mbits/sec, that's
    not going to be a problem even to 300 meters. At 100baseTX, it's
    probably way over the spec.


    --
    # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
    # 831.336.2558 voice http://www.LearnByDestroying.com
    # jeffl@comix.santa-cruz.ca.us
    # 831.421.6491 digital_pager jeffl@cruzio.com AE6KS
  19. Archived from groups: alt.internet.wireless (More info?)

    > Ethernet waveforms are suppose to square waves, not ramps, although an
    > ugly triangular waveform is what usually comes out of a bandwidth

    Yes except that a square wave produces ugly harmonics hence the aim
    shouldn't be a square wave but a very rapid rising voltage but not quite
    square and that was all I was referring to. However, that's splitting
    hairs and doesn't add to the discussion. My interest/recollection of
    transmission line theory appears to be nowhere near as good as yours. :)

    > highest frequency in any specified category." At 10Mbits/sec, that's
    > not going to be a problem even to 300 meters. At 100baseTX, it's
    > probably way over the spec.

    Yes and in 1985 100Mbps wasn't exactly run of the mill 10base2.

    David.
  20. Archived from groups: alt.internet.wireless (More info?)

    On Wed, 30 Jun 2004 16:50:20 +0100, David Taylor
    <djtaylor@bigfoot.com> wrote:

    >> Ethernet waveforms are suppose to square waves, not ramps, although an
    >> ugly triangular waveform is what usually comes out of a bandwidth

    >Yes except that a square wave produces ugly harmonics hence the aim
    >shouldn't be a square wave but a very rapid rising voltage but not quite
    >square and that was all I was referring to.

    Well, I know what you're trying to say, but you're doing it all wrong.
    Fourier worked it out 200 years ago.

    A square wave is composed of a fundamental sine wave and a mess of odd
    order harmonics, all of which have a zero degree phase shift to the
    fundamental. For an ideal 50% duty cycle square wave, 1/3 of the
    power it tied up in these harmonics. Varying the duty cycle move some
    of the fundamental power into the harmonics. The narrower the pulse
    width, the more harmonics.

    Drivel: If the waveform is asymmetrical, there are even harmonics
    present.

    What a coax or twisted pair cable does is screw things up in two ways,
    amplitude and phase. In amplitude, the -10dB/decade frequency rolloff
    of the typical coax cable causes more attenuation at higher
    frequencies. Therefore, the harmonics get reduced in output more than
    the fundamental. The resultant waveform ends up with longer
    (non-vertical) rise and fall times, which are the high frequency
    components of the waveform. (The flat parts are the low frequency
    components). Eventually it starts to resemble a trapazoid or triangle
    instead of a square wave. Fig 5 in the previous URL is a good example
    of what comes out.

    The phase shift of the cable is more pronounced at higher frequencies
    than at lower frequencies. This causes the harmonic components of the
    square wave to shift in phase relative to the fundamental sine wave.
    This results in a rather ugly waveform. However, if the cable is
    properly matched, and of good quality, the degree of phase shifting is
    fairly nominal for 10baseT and little distortion results. As long as
    the 3rd and perhaps the 5th harmonics are in phase and present, the
    waveform will sufficiently resemble a square wave to be decoded
    properly by the 10baseT or 10base2 transceiver. The higher harmonics
    are of little consequence.

    Incidentally, I find harmonics to be quite beautiful and not at all
    ugly.

    >However, that's splitting
    >hairs and doesn't add to the discussion. My interest/recollection of
    >transmission line theory appears to be nowhere near as good as yours. :)

    Y'er doing fine. However, I cheat. In a past life, I played RF
    engineer for a variety of radio and telecom companies.

    >> highest frequency in any specified category." At 10Mbits/sec, that's
    >> not going to be a problem even to 300 meters. At 100baseTX, it's
    >> probably way over the spec.

    >Yes and in 1985 100Mbps wasn't exactly run of the mill 10base2.
    >David.


    --
    # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
    # 831.336.2558 voice http://www.LearnByDestroying.com
    # jeffl@comix.santa-cruz.ca.us
    # 831.421.6491 digital_pager jeffl@cruzio.com AE6KS
  21. Archived from groups: alt.internet.wireless (More info?)

    > Incidentally, I find harmonics to be quite beautiful and not at all
    > ugly.

    Can I scream RFI?! :)

    > Y'er doing fine. However, I cheat. In a past life, I played RF
    > engineer for a variety of radio and telecom companies.

    My interest when I did any of this was as a digital electronics hardware
    designer and obviously, we're only interested in avoiding those
    harmonics and getting the nice clean 1's and 0's. If in doubt sample
    the bugger and process it to death. ;)

    Last time I did FFT's was oooh, about 20 something years ago and I
    wasn't particularly interested in them at the time for some bizarre
    reason, think it was girls. :)

    David.
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