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PICList Thread
'Morse Code Modems'
1999\08\27@011613 by Russell McMahon

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More detail would help.

- Is this by telephone (???) or radio or ???
- Describe how the overall system works.
- Knowing WHY this is done would be interesting.

- The 7910 "worldchip" modem IC may still be available ([possibly surplus)
allowing roll yer own still.
- There are other modem IC's that would handle the data rate.

Depending on how this all works it may be possible to make a very cheap and
simple modem adequate to the task using a single tone decoder IC eg
LM567!!! or a 4046 PLL IC or XR... or ....

I am puzzled as to why a modem is needed at all unless there is some arcane
extra feature that you have not mentioned. If you use an audio circuit then
the USER is the modem received with Morse. If you are using eg a multipoint
digital data network it may make sense.

regards



               Russell McMahon
               - - o o     o - o o    o - - - -     o -    - o     - o - o
:-)



================================================


From: McMeikan, Andrew <spam_OUTandrew.mcmeikanTakeThisOuTspamMITSWA.COM.AU>
>        I have been asked by some Morse coders to explore the possibility
>of using a micro to set an AT-command style modem into 300 baud to
>communicate via a hand operated Morse key.
>
>  At the moment these guys are using dumb modems to send Morse

Why?

? to each other all over Australia,

via what medium

>dumb 300 baud modems are getting harder to come
>by so they are looking at using smart modems with a 'little black box' to
>handle setting the right mode and interfacing to the key and sounder.
>

1999\08\27@094245 by paulb

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Russell McMahon wrote:

> More detail would help.

 As always.  From my understanding:

> - Is this by telephone (???) or radio or ???

 Telephone.  Paying STD rates which are now limited to $3.00 between
19:00 and 00:00 local.  Yes, it *is* cheaper to use the radio, but
apparently some of these enthusiasts are actually not Amateurs!

> - Describe how the overall system works.

 Key and sounder each end.

> - Knowing WHY this is done would be interesting.

 *Not* a useful question to ask a Morse fanatic!

> - The 7910 "worldchip" modem IC may still be available ([possibly
> surplus) allowing roll yer own still.

 It is a "legacy" part mostly available ready assembled inside 1200
baud modems.  The assertion (which I find curious but...) is that these
are becoming hard to find second hand.  I would have thought they were
rife and to be had for nothing.  I collect them occasionally at garage
sales, usually for a dollar or two (albeit, may have to buy the whole
computer!).

> - There are other modem IC's that would handle the data rate.
> Depending on how this all works it may be possible to make a very
> cheap and simple modem adequate to the task using a single tone
> decoder IC eg LM567!!! or a 4046 PLL IC or XR... or ....

 The users are nervous about hacking telecom stuff, legality, type
approval and all that.  Besides, that involves *work*!

> I am puzzled as to why a modem is needed at all unless there is some
> arcane extra feature that you have not mentioned.  If you use an audio
> circuit then the USER is the modem received with Morse.

 Dead right.  The "arcane extra feature" happens to be the use of
sounders for *real* Morse.  Many of these sites are historic locations
such as Timbertown at Wauchope NSW (near here).  Now it makes sense,
doesn't it?

> If you are using eg a multipoint digital data network it may make
> sense.

 Not so easy to set up using telephone lines (as requires multiple
lines).  I have proposed that using a contemporary modem and a
pre-processor (e.g. PIC = On toPIC) to send a stream of ASCII events
marked with a local clock would allow 100% faithful reproduction albeit
with a delay (maybe 1 second or so), like Speak Freely etc.

 Long breaks would allow easy re-synchronisation (a "reset" event)
This would be readily adaptable to Internet networking and "nets" etc.
with simple hardware.

 But they (being by definition, backward-looking) say they want
backward-compatibility with the present un-framed system which as I have
pointed out, just isn't "on"!
--
 Cheers,
       Paul B.

1999\08\27@095643 by Michael Rigby-Jones

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The whole thing seems a little bizzare to me, sending dit's and dah's down a
perfectly good voice network....but then I don't use morse code <g>

Why can't the morse key be connected to a (very) simple tone generator,
acoustically coupled to a telephone.  A matching tone decoder acoustically
coupled to the telephones ear piece would do the receiving.  It wouldn't
even have to be DTMF.  In fact, the tone detector could be just a simple
detector and comparator as long as vast amounts of static aren't a problem.
A few $'s of parts maximum, and no legality problems connecting stuff to the
telco.

A modem just seems absolute overkill in every way.

Regards

Mike Rigby-Jones


> {Original Message removed}

1999\08\27@101347 by paulb

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Michael Rigby-Jones wrote:

> Why can't the morse key be connected to a (very) simple tone
> generator, acoustically coupled to a telephone.  A matching tone
> decoder acoustically coupled to the telephones ear piece would do the
> receiving.
...
> A few $'s of parts maximum, and no legality problems connecting stuff
> to the telco.

 According to my discussions with the previous poster (I forget
whether on-list or off now), even acoustic couplers are required to be
type-approved.

 Also, it is more difficult to couple to "square" handsets!

 Well, that's what I was told!
--
 Cheers,
       Paul B.

1999\08\27@125359 by Wagner Lipnharski
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"Paul B. Webster VK2BZC" wrote:
>   According to my discussions with the previous poster (I forget
> whether on-list or off now), even acoustic couplers are required to be
> type-approved.

Yes, there are few standards, you can not inject "audio" levels higher
than zero db (or dbm?) at phone lines, according to something I read
many years ago... it could be complete different now... :)

1999\08\27@144158 by Dave VanHorn

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> Yes, there are few standards, you can not inject "audio" levels higher
> than zero db (or dbm?) at phone lines, according to something I read
> many years ago... it could be complete different now... :)

-9dBm

1999\08\28@192435 by Dennis Plunkett

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At 12:52 27/08/99 -0400, you wrote:
>"Paul B. Webster VK2BZC" wrote:
>>   According to my discussions with the previous poster (I forget
>> whether on-list or off now), even acoustic couplers are required to be
>> type-approved.
>
>Yes, there are few standards, you can not inject "audio" levels higher
>than zero db (or dbm?) at phone lines, according to something I read
>many years ago... it could be complete different now... :)
>
>


The level is -10dBm ,but, ask your local telco what level the howler tone
is sent at!
But on the other hand you (Being the user) have to ensure that the level at
the MDF (Entry point to the exchange) is no more than -11dBm (Most cables
are matched to provide a 3dBr drop. So in a modem situation the levels are
like this

                                       *** MODEM ***
Originate       Cable           Exchange (Digital)      Cable           Terminat
e

-11dBm          -3dB                    -6dB            -3dB            0dB
-11             -14                     -20             -23             -23

                               Exchange (Analogue//digital hybrid)
                                       -6 to -12dB

                                       *** VOICE***

+3dBr           -3dB                    -6dB            -3dB            0dB
X level                                                         X level -12dB
(Human voice average = -15dBm)



Dennis

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