T
tony sayer
- Jan 1, 1970
- 0
Eeyore <rabbitsfriendsandrel said:Or up to 24 Mbps ADSL2+ !
Graham
When you live -in- an exchange that is;!...
Eeyore <rabbitsfriendsandrel said:Or up to 24 Mbps ADSL2+ !
Graham
Ross said:On Tue, 06 Jan 2009 04:53:17 -0900, [email protected] (Floyd L. Davidson) wrote:
:>On Sun, 04 Jan 2009 20:36:09 -0900, [email protected] (Floyd L. Davidson)
wrote:
:>
:>:
:>:> voice frequency circuits were all 300 - 3400Hz in my day.
:>:
:>:The PSTN is specified from 400 to 2800 Hz, with 24 dB SNR.
:>:
:>:Individual channels on various carrier systems, and some
:>rivate line voice circuits are specified with more
:>:bandwidth.
:>:
:>
:>In Australia PSTN is specified for 300 - 3400 Hz bandwidth.
:
:I doubt it.
Well let's give some examples...
When I was involved in junction commissioning (unloaded copper inter-exchange VF
junctions) with Telstra, transmission measurements were carried out over the
300-3400Hz range. This hasn't altered.
When looking at the transmission characteristics of an international telephone
exchange (ITU-T Recommendations)the only frequency range mentioned is
300-3400Hz.
http://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-Q.45-198410-I!!PDF-E&type=items
http://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-Q.45bis-198811-I!!PDF-E&type=items
And the following document recommends all channel terminal equipment be lined up
using 300-3400Hz.
http://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-G.120-199812-I!!PDF-E&type=items
Note that ITU-T G235 (3KHz spacing) is supesrseded and is no longer recommended
for international connections.
As for the specification relating to customer equipment connected to the PSTN
the frequency range used for testing is 100Hz - 4KHz.
http://www.commsalliance.com.au/documents/standards/S004:2008
In other documents from this website the definition of VF telephony or Voiceband
is 300-3400Hz.
There probably a number of other publications if I had the time to research them
but suffice to say that in Australia the VF telephony channel bandwidth is
specified as per ITU recommendations ie. 300-3400Hz.
Ross Herbert said:On Wed, 07 Jan 2009 06:52:48 -0900, [email protected] (Floyd L. Davidson) wrote:
:>
:>Good, accurate stuff, Ross.
:
:All of it referenced the specifications for individual
:channels on various facilities. None of it had to do
:with the overall minimum allowed specification for an
:end to end connection via the PSTN.
Hold it, that's a dumb statement.
The ITU recommendation for international VF channel bandwidth is 300-3400Hz, so
why would it be necessary to "allow a minimum" bandwidth of 400-2800Hz? If the
300-3400Hz applies to ALL channels used in an end-to-end international link,
then it follows that the overall bandwidth is 300-3400Hz.
Floyd L. Davidson said:ITU-T standards and Bellcore standards.
Ross said::
:A proper 600:600 transformer will be more expensive than a 10k:10k one too.
:
That may be true but how many readily available 10K:10K audio transformers have
a 3.5Kv isolation rating?
Eeyore said:I believe this was required IIRC for only brief use. He could avoid using it during
thunderstorms too.
http://uk.farnell.com/triad-magnetics/ty-141p/transformer-audio-0-1w/dp/1610409
Probably in stock at Newark
Why? That takes the fun out of it!Eeyore said:Ross Herbert wrote:
I believe this was required IIRC for only brief use. He could avoid using it during
thunderstorms too.
Wecan do it said:What do you suppose happens to the bandwidth of a signal as it
is passed through successive audio devices that are band
limited to 300-3400 Hz?
Would you expect to get 300-3400Hz +- ndB response in an end
to end loopback test when you use white noise as the test
signal? (n =ITU spec)
Going from a handset to a PBX to MUX to a CO into the network
and back if each device has a 300-3400Hz response the looped
back signal should be more band limited than the first device
in the signal chain with 300-3400Hz response originating test
signal by quite some bit.
Peace
dawg
In uk.telecom Stuart said:It is always grounded, directly or indirectly, otherwise the screen fails
to be effective.
So how does phantom power work then? You stick a voltage down the signal
leads in parallel and the the return is via what?
Floyd L. Davidson said:In the context presented, that is generally true... but
I'd like to point out that the shielding on multipair
telephone cables is 1) grounded, 2) commonly conducts
current, and 3) the noise reduction provided is
*enhanced* by the current!
Both ends of the cable are well grounded and any induced
current in the shield will be greater than in any
individual cable pair. The current in the shield
induces an opposite current into the cable pair, thus
reducing the total noise signal in each pair.