17 Apr
2014
17 Apr
'14
9:24 p.m.
Can you run thru the asterisk POTS line cars with the frequencies, etc,
or do those only handle voice grade frequencies?
I am suspecting not, but sounds like a good place to ask the question.
thanks
jim
On 4/17/2014 8:57 PM, drlegendre . wrote:
@Mark
If you need a set of Model 100/102 cups, shoot me a mail off-list. I have a
single set here that I'm a bit loath to let go, but maybe we can work out a
trade - or at least a secure loan?
And I swear that I'm not a pimp for Viking Electronics, but they make a
device called a DLE-300 which is essentially a micro-sized Telco Central
Office (with two lines) that sits on your desk. Think of it as two
telephone lines, with different numbers, that both run to your desk. Call 1
from 2, 2 from 1, and use all kinds of features like call waiting, call
progress etc.
In short, you can jack-in with an RJ-11 cable from an analog POTS set or
modem on each of its two ports (line 1 & line 2) and make very well
simulated high-bandwidth "calls" from one line to the other. Works like a
gem for local modems up to 128K on each side..
On Thu, Apr 17, 2014 at 3:46 PM, Joachim Thiemann <
joachim.thiemann at gmail.com> wrote:
On 17 April 2014 06:31, Mark J. Blair <nf6x at
nf6x.net> wrote:
Have any of y'all tried using one of those
novelty "retro" cell phone
handsets in an acoustic coupled modem? I
wonder whether their output level
and mic sensitivity are sufficient, and whether their dimensions are close
enough to a good ol' Model 500 handset to fit an acoustic coupler well.
I may just order one up and try it, but I figured
I'd ask if anybody
else has tried it first. It would be silly fun to dial up
over my iPhone
with an acoustic coupler attached to my TRS-80 Model 100, or the DEC LA12
Correspondent terminal I have on the way from the ePlace. Not that I know
of any 300 baud modems to call up, though...
I haven't tried it, but having worked in the field of codecs for cell
phones (AMR-WB, VMR-WB and AMR-WB+ to be specific) I would caution you
that the codecs on modern, digital phones are not at all designed for
modem-type signals (eg QPSK etc) which - in their design - assume
mostly linear channels with some bandwidth and noise floor.
At low enough speeds (and 300 baud ought to qualify) the nonlinear
distortion that the CELP codecs will introduce might not matter, but
if it's RCELP (regularized or relaxed CELP) it is very much designed
to modify the pitch imperceptibly to humans which would cause bit
errors for any modem signal. (But I don't know of any RCELP in the GSM
or CDMA standards, so this might not matter)
In short, try it, but I'd be sceptical that you'd get good results.
I suggest a different approach. Write an iOS or Android app that
captures the mic and controls the speaker of the handset; do the
modulating/demodulating on the phone, then the app can pass the data
over ssh/telnet to a net-connected BBS. Or pass it to an emulated
machine on the phone. (I've seen SIMH for Android - not sure about
iOS).
(I've been a TA for an undergraduate-level DSP course where students
implemented 4-QPSK in C on a TI eval board (I designed that experiment
with a nod to classic computing in mind) - I believe that could get
you up to the 2400 baud standard, but with an acoustic coupler you
couldn't go that high anyways. I can't remember if 300 Baud is
actually simple frequency-shift keying (FSK) which is very simple to
understand and implement)
Cheers,
Joachim.
--
Joachim Thiemann :: http://jthiem.bitbucket.org ::
http://signalsprocessed.blogspot.com