Does anyone know what are the highest and lowest frequencies that can
be transmitted as CW over a commercial wired telephone network?

Could bypassing the mic and speaker extend this range?

Paul Ingram

On Thu, 04 Mar 2010 05:02:30 GMT, p...@oslotec.com (Paul Ingram) wrote:

>Does anyone know what are the highest and lowest frequencies that can
>be transmitted as CW over a commercial wired telephone network?

POTS is limited at the upper end by the DACs.  They use 8k samples per second,
so that's ideally a 4kHz bandwidth.  I'm not sure what the low end limiter is,
but it's supposed the spec is 300Hz.
 
>Could bypassing the mic and speaker extend this range?

No.

On Thu, 04 Mar 2010 05:02:30 GMT, p...@oslotec.com (Paul Ingram)
wrote:

>Does anyone know what are the highest and lowest frequencies that can
>be transmitted as CW over a commercial wired telephone network?
>
>Could bypassing the mic and speaker extend this range?
>
>Paul Ingram


 Ask Floyd L. Davidson up in alt.engineering.electrical

On Wed, 03 Mar 2010 23:10:18 -0600, "k...@att.bizzzzzzzzzzzz"
<k...@att.bizzzzzzzzzzzz> wrote:

>On Thu, 04 Mar 2010 05:02:30 GMT, p...@oslotec.com (Paul Ingram) wrote:
>
>>Does anyone know what are the highest and lowest frequencies that can
>>be transmitted as CW over a commercial wired telephone network?
>
>POTS is limited at the upper end by the DACs.  They use 8k samples per second,
>so that's ideally a 4kHz bandwidth.  I'm not sure what the low end limiter is,
>but it's supposed the spec is 300Hz.
><snip>

Bandwidth is specified as 300Hz - 3000Hz.  2700Hz width.  Not
4k.  They may provide more, but my more recent tests suggest
they hard limit it pretty close these days.  Back when
(1950's), it was much more.

I've got a copy of the official specifications on the shelf,
if anyone needs specific citations.  They are designed to
cover different phone and switching systems, but they all
agree on this point.

There was a ruckus some years after when tape players made it
into business places after WW II (german invention discovered
in captured tanks, I think) where some folks would tape at
normal speed and play fast for international calls to short
the time (and expense), allowing the other side to record
fast and then play back slower.  I think that was part of the
first "why" that AT&T started figuring it was worth some
trouble to start sticking low pass filters in the line.

That's the story I heard and I'm sticking to it.  But I have
no real idea, at all.  Sounded good when I heard it, maybe 30
years back, though.

Anyway, the easiest way to tell is just sit at a piano, hit
keys, and let the other side tell you when it goes "clunk,
clunk" instead of a nice tone.

Jon

On Wed, 03 Mar 2010 22:05:18 -0800, Jon Kirwan
<j...@infinitefactors.org> wrote:

>On Wed, 03 Mar 2010 23:10:18 -0600, "k...@att.bizzzzzzzzzzzz"
><k...@att.bizzzzzzzzzzzz> wrote:
>
>>On Thu, 04 Mar 2010 05:02:30 GMT, p...@oslotec.com (Paul Ingram) wrote:
>>
>>>Does anyone know what are the highest and lowest frequencies that can
>>>be transmitted as CW over a commercial wired telephone network?
>>
>>POTS is limited at the upper end by the DACs.  They use 8k samples per second,
>>so that's ideally a 4kHz bandwidth.  I'm not sure what the low end limiter is,
>>but it's supposed the spec is 300Hz.
>><snip>
>
>Bandwidth is specified as 300Hz - 3000Hz.  2700Hz width.  Not
>4k.  They may provide more, but my more recent tests suggest
>they hard limit it pretty close these days.  Back when
>(1950's), it was much more.
>
>I've got a copy of the official specifications on the shelf,
>if anyone needs specific citations.  They are designed to
>cover different phone and switching systems, but they all
>agree on this point.
>
>There was a ruckus some years after when tape players made it
>into business places after WW II (german invention discovered
>in captured tanks, I think) where some folks would tape at
>normal speed and play fast for international calls to short
>the time (and expense), allowing the other side to record
>fast and then play back slower.  I think that was part of the
>first "why" that AT&T started figuring it was worth some
>trouble to start sticking low pass filters in the line.
>
>That's the story I heard and I'm sticking to it.  But I have
>no real idea, at all.  Sounded good when I heard it, maybe 30
>years back, though.
>
>Anyway, the easiest way to tell is just sit at a piano, hit
>keys, and let the other side tell you when it goes "clunk,
>clunk" instead of a nice tone.
>
>Jon

Originally one pair of wires sent one long-distance call. Then, to
save wire, a bunch of calls were sent SSB over one pair, over
close-spaced carriers. The Western Electric "J" system used 4 KHz
channel spacings, so the baseband audio was sharply filtered between
300 and 2600 Hz to avoid channel-channel crosstalk.

Later digital systems sampled at 8 KHz, so an antialiasing filter
preceded the digitizer, usually about 2700 Hz.

The tape recorder thing doesn't make much sense. International phone
lines never had enough bandwidth to allow that trick.

John

On Wed, 03 Mar 2010 22:23:22 -0800, John Larkin
<j...@highNOTlandTHIStechnologyPART.com> wrote:

>On Wed, 03 Mar 2010 22:05:18 -0800, Jon Kirwan
><j...@infinitefactors.org> wrote:
>
>>On Wed, 03 Mar 2010 23:10:18 -0600, "k...@att.bizzzzzzzzzzzz"
>><k...@att.bizzzzzzzzzzzz> wrote:
>>
>>>On Thu, 04 Mar 2010 05:02:30 GMT, p...@oslotec.com (Paul Ingram) wrote:
>>>
>>>>Does anyone know what are the highest and lowest frequencies that can
>>>>be transmitted as CW over a commercial wired telephone network?
>>>
>>>POTS is limited at the upper end by the DACs.  They use 8k samples per second,
>>>so that's ideally a 4kHz bandwidth.  I'm not sure what the low end limiter is,
>>>but it's supposed the spec is 300Hz.
>>><snip>
>>
>>Bandwidth is specified as 300Hz - 3000Hz.  2700Hz width.  Not
>>4k.  They may provide more, but my more recent tests suggest
>>they hard limit it pretty close these days.  Back when
>>(1950's), it was much more.
>>
>>I've got a copy of the official specifications on the shelf,
>>if anyone needs specific citations.  They are designed to
>>cover different phone and switching systems, but they all
>>agree on this point.
>>
>>There was a ruckus some years after when tape players made it
>>into business places after WW II (german invention discovered
>>in captured tanks, I think) where some folks would tape at
>>normal speed and play fast for international calls to short
>>the time (and expense), allowing the other side to record
>>fast and then play back slower.  I think that was part of the
>>first "why" that AT&T started figuring it was worth some
>>trouble to start sticking low pass filters in the line.
>>
>>That's the story I heard and I'm sticking to it.  But I have
>>no real idea, at all.  Sounded good when I heard it, maybe 30
>>years back, though.
>>
>>Anyway, the easiest way to tell is just sit at a piano, hit
>>keys, and let the other side tell you when it goes "clunk,
>>clunk" instead of a nice tone.
>>
>>Jon
>
>Originally one pair of wires sent one long-distance call. Then, to
>save wire, a bunch of calls were sent SSB over one pair, over
>close-spaced carriers. The Western Electric "J" system used 4 KHz
>channel spacings, so the baseband audio was sharply filtered between
>300 and 2600 Hz to avoid channel-channel crosstalk.

There remains the tariffs for POTS which state 300Hz to
3000Hz as the required bandpass.  I believe I must have read
them more than a few times, by now.

>Later digital systems sampled at 8 KHz, so an antialiasing filter
>preceded the digitizer, usually about 2700 Hz.
>
>The tape recorder thing doesn't make much sense. International phone
>lines never had enough bandwidth to allow that trick.

It was one of those tales I heard from someone working at the
phone company, back then.  I frankly had (and have) no idea.

Jon

Paul Ingram wrote:
> Does anyone know what are the highest and lowest frequencies that can
> be transmitted as CW over a commercial wired telephone network?
> 
> Could bypassing the mic and speaker extend this range?
> 
> Paul Ingram
   I think the bandwidth is supposed to be 3KHz, but do mot know if that 
is the 3dB point and do not know the rolloff rate.
   However, traditionally (ie up to 5 years ago and maybe later) one 
could *reliably* get 48Kbaud data rate with a modem.
   But (some??) telcos have deliberately, in some unknown manner, 
throttled that so the best one can now do is 28.8Kbaud.
   And the response from then as well as from PUCs is "all we are 
required to support is VOICE QUALITY".
   BARF!
   AFAIK there is not a goddamn thing anyone can do about that.
   I say it will get worse as the greed of telcos will allow them to 
decrease that to maybe a max of 1Kbaud.
   Why? so that dial-up "customers" will get so fed up with slow 
internst that they will pay $$$ for "high speed" (which seems to never 
be as fast as advertised - and definitely not as reliable as dial-p).

k...@att.bizzzzzzzzzzzz wrote:
> On Thu, 04 Mar 2010 05:02:30 GMT, p...@oslotec.com (Paul Ingram) wrote:
> 
>> Does anyone know what are the highest and lowest frequencies that can
>> be transmitted as CW over a commercial wired telephone network?
> 
> POTS is limited at the upper end by the DACs.  They use 8k samples per second,
> so that's ideally a 4kHz bandwidth.  I'm not sure what the low end limiter is,
> but it's supposed the spec is 300Hz.
>  
>> Could bypassing the mic and speaker extend this range?
> 
> No.
   Please comment as to WTF telcos did to throttle dial-up from 48Kbaud 
to 28.8Kbaud.

Paul Ingram wrote:
> Does anyone know what are the highest and lowest frequencies that can
> be transmitted as CW over a commercial wired telephone network?
> 
> Could bypassing the mic and speaker extend this range?
> 
> Paul Ingram

"The" telephone channel is usually specified as 300..3400 Hz. This is 
what is guaranteed to be transmitted to anywhere on the world. The 
bandwidth of the transmission line between you and the first electronic 
gadget it meets is from dc to something that is specific to each case.

Pere

Robert Baer <r...@localnet.com> wrote in news:-
a...@posted.localnet:

> Paul Ingram wrote:
>> Does anyone know what are the highest and lowest frequencies that can
>> be transmitted as CW over a commercial wired telephone network?
>> 
>> Could bypassing the mic and speaker extend this range?
>> 
>> Paul Ingram
>    I think the bandwidth is supposed to be 3KHz, but do mot know if that 
> is the 3dB point and do not know the rolloff rate.
>    However, traditionally (ie up to 5 years ago and maybe later) one 
> could *reliably* get 48Kbaud data rate with a modem.

I'm still on dialup,and I usually log on at 48K,according to the W98SE 
taskbar indicator.Sometimes,it logs on at 49K,but it's never stable.
ISTR that the max limit was 52K,but was usually limited by coils in the 
lines.


Century Link in central Florida is my telco.

-- 
Jim Yanik
jyanik
at
localnet
dot com