hcooper@esunix.UUCP (Harrison Cooper) (08/16/89)
I have a couple of 300 baud modems, one is a Radio Shack external, and the other is an old acoustic coupler type (I don't have either one in front of me right now, so no part numbers available). The question is can they be upgraded to 1200 or more? I have posted this before I have opened either one up, so I don't know what devices they are using. I don't have a schematic for the acoustic type (paid $3.00 for it), so the RS unit is probably a better unit to play with. I don't care if it can be programmed by serial, just hardwired for the baud rate. E-mail or post. Thanks in advance H. Cooper N7KST utah-cs!esunix!hcooper
logajan@ns.network.com (John Logajan) (08/17/89)
In article <1436@esunix.UUCP>, hcooper@esunix.UUCP (Harrison Cooper) writes: > The question is can they be upgraded to 1200 or more? I have posted Only in the sense that a VW can be upgraded to a Rolls, by replacing every part! -- - John M. Logajan @ Network Systems; 7600 Boone Ave; Brooklyn Park, MN 55428 - - logajan@ns.network.com / ...rutgers!umn-cs!ns!logajan / john@logajan.mn.org -
brian@ucsd.EDU (Brian Kantor) (08/17/89)
HCooper asks if his 300 bps modem can be upgraded to 1200 bps or faster. The answer is "Not really." The case, power supply, connectors, and controls are probably reusable. The modem circuitry isn't, except perhaps the part that interfaces to the telephone line. An ambitious and skilled worker COULD chop out much of the existing modem circuitry and replace it with something like the WORLDCHIP or some other single-chip modem, but that is an incredible amount of work and might not be easier than building your own from scratch. So while it's not impossible, it's probably too much work. - Brian
ken@cs.rochester.edu (Ken Yap) (08/17/89)
Yeah, modems are mass market items now. Would be cheaper to buy a 1200 modem than to try to upgrade the 300 modem. Donate the 300 modem to a charity wanting a modem.
deanr@sco.COM (Dean Reece) (08/18/89)
In article <1436@esunix.UUCP> hcooper@esunix.UUCP (Harrison Cooper) writes: >I have a couple of 300 baud modems, one is a Radio Shack external, and >the other is an old acoustic coupler type (I don't have either one in >front of me right now, so no part numbers available). > >The question is can they be upgraded to 1200 or more? I have posted >this before I have opened either one up, so I don't know what devices >they are using. I don't have a schematic for the acoustic type (paid >$3.00 for it), so the RS unit is probably a better unit to play with. >I don't care if it can be programmed by serial, just hardwired for the >baud rate. E-mail or post. No, can't be done. You can PROBABLY use the RS modem (a DC1?) up to 600 bps as is, but you need something on the other end expecting it. I doubt the acustic couple modem will run above 300 bps without the ber skyrocketing. This may also happen with the direct connect modem; I've never tried it, but the standard allows for it: (I think) (bps = bits per second & ber = bit error rate) bps: Encoding: Baud: Bits/Baud: Orig Carrier: Ans Carrier: 0-600 FSK (FM) 0-600 1 1050/1250? hz 2025/2225? hz 1200 PSK 600 2 1200 hz 2400 hz 2400 PSK 600 4 1200 hz 2400 hz The most important difference between 300 bps modems and all others is that the slow ones use FSK (frequency shift keying). This means that the modem shifts frequences depending on the bit you are sending (I think 0=1050 hz & 1=1250 hz, but its been a while). This allows TOTALLY ASYNCHRONUS data to be sent, meaning ANY bps rate can be used up to the limit of the channel. PSK encoding (phase shift keying) encodes the data by keeping the frequency constant and shifting the phase forward or backward by so many degrees for each bit PAIR (or more) being transmitted. (a bit pair is called a di-bit) You really can't convert the modem itself without totally replacing the encoding/decoding & filtering circuits (and that is most of what a modem is). A technical note: Calling a 2400 bps modem a 2400 baud modem is incorrect. They are actually 600 baud (each baud contains 4 bits). For conversation, either is acceptable, but its worth knowing anyway. (the same goes for a 1200 bps modem as well) Hope it helps. -- Dean Reece (deanr@sco.COM) (408)458-1422 The Santa Cruz Operation, P.O.Box 1900, Santa Cruz, CA 95061
phil@diablo.amd.com (Phil Ngai) (08/18/89)
In article <1905@ucsd.EDU> brian@ucsd.edu (Brian Kantor) writes: |An ambitious and skilled worker COULD chop out much of the existing |modem circuitry and replace it with something like the WORLDCHIP or |some other single-chip modem, but that is an incredible amount of work |and might not be easier than building your own from scratch. Thanks for the plug, Brian, but I would guess he wanted 1200 full duplex, or Bell 212 mode. The WORLDCHIP (tm) can only do 1200 half duplex, V22 or something like that. A brand new modem is pretty cheap these days and I would just buy a new one. -- Phil Ngai, phil@diablo.amd.com {uunet,decwrl,ucbvax}!amdcad!phil "Nonviolence works! India hasn't had to use their nuclear weapons yet."
pcf@galadriel.bt.co.uk (Pete French) (08/18/89)
From article <1436@esunix.UUCP>, by hcooper@esunix.UUCP (Harrison Cooper): > > The question is can they be upgraded to 1200 or more? I have posted > this before I have opened either one up, so I don't know what devices > they are using. You will need to change the filters , the oscillators and the demodulator. On an old modem you may have a chance. The filters can probably be changed by simply altering all the resistors and capacitors around them. This will then allow you to use the FSK tones necessary for the different standard. The oscillators can probably bo modified similarly to generate the necessary tones when presented with a mark or a space. It depends upon how they are constructed... The major problem will probably be with the demodulation. If this is just done with a pair of filters then you may have a chance... however it is most likely to be done with a PLL or similar in which case its "data sheet time". If you open it up and its an all-transistor and relays unit then you may have a chance. If its got any IC's in it then forget it. Its easier to build your own from an AM7910. You could probably salvage and Level Shifting circuits for the RS232 and the coupling to the line - but trash the 'tronix. -Pete. -- -Pete French. | British Telecom Research Labs. | "The carefree days are distant now, Martlesham Heath, East Anglia. | I wear my memories like a shroud..." All my own thoughts (of course) | -SIOUXSIE
makela@tukki.jyu.fi (Otto J. Makela) (08/19/89)
In article <3194@scolex.sco.COM>, deanr@sco.COM (Dean Reece) says: >(bps = bits per second & ber = bit error rate) >bps: Encoding: Baud: Bits/Baud: Orig Carrier: Ans Carrier: >0-600 FSK (FM) 0-600 1 1050/1250? hz 2025/2225? hz >1200 PSK 600 2 1200 hz 2400 hz >2400 PSK 600 4 1200 hz 2400 hz >The most important difference between 300 bps modems and all others is that >the slow ones use FSK (frequency shift keying). This means that the modem >shifts frequences depending on the bit you are sending (I think 0=1050 hz & >1=1250 hz, but its been a while). This allows TOTALLY ASYNCHRONUS data to >be sent, meaning ANY bps rate can be used up to the limit of the channel. Well, there exists a thing called CCITT V.23, which is 1200/75 b/s split- speed FSK. This is basically the same thing as the 300 b/s FSK's, but with different frequencies, and the 75 b/s "back channel" really squeezed up so it doesn't get in the way of the 1200 b/s channel; sorry, it's such a long time that I don't remember the frequencies. This actually made a lot of sense in the bad old days when modems were built from discretes and lotsa gates, as very few users constantly maintain a typing speed >7.5 chars per second (@ start bit, 7 bits data, even parity, one stop bit). This was used a lot in the UK, on the British Telecom Prestel(tm) system (and on many clones all around the world). There was also a method for signalling channel turn-around, making bidirectional data transfers possible. >PSK encoding (phase shift keying) encodes the data by keeping the frequency >constant and shifting the phase forward or backward by so many degrees for >each bit PAIR (or more) being transmitted. (a bit pair is called a di-bit) I've also seen the CCITT V.22bis (that's 2400 b/s for all americanos out there) called "Quadrature Amplitude Modulation", is this just techno-talk hype for PSK with the 4-bit codings ? >You really can't convert the modem itself without totally replacing the >encoding/decoding & filtering circuits (and that is most of what a modem >is). Agreed. Converting the 300 b/s things to anything else would most probably be more trouble than it was worth. Might be educational, though... -- * Otto J. Makela (makela@jyu.fi, MAKELA_OTTO_@FINJYU.BITNET) * * Phone: +358 41 613 847, BBS: +358 41 211 562 (CCITT, Bell 2400/1200/300) * * Mail: Kauppakatu 1 B 18, SF-40100 Jyvaskyla, Finland, EUROPE * * * * freopen("/dev/null","r",stdflame); * * * * * * * * * * * * * * * * * *
ce1zzes@prism.gatech.EDU (Eric Sheppard) (08/22/89)
> >I've also seen the CCITT V.22bis (that's 2400 b/s for all americanos out >there) called "Quadrature Amplitude Modulation", is this just techno-talk >hype for PSK with the 4-bit codings ? Quadrature Amplitude Modulation is the combination of both FSK and PSK modulation methods. The data stream is both phase AND frequency shifted. Sounds confusing? You bet it is! The main difficulty in detecting the QAM signal lies in regenerating the original carrier; both the frequency of the originating system's carrier and its phase must be recovered from the transmitted signal. I've only started studying digital communications systems, and I'm overwhelmed by their complexity, both in design and implementation. Could anyone tell me which systems today's modems use? Is it QPSK, 8PSK, or 8QAM? Eric Sheppard Georgia Institute of Technology, Atlanta Georgia, 30332 uucp: ...!{allegra,amd,hplabs,seismo,ut-ngp}!gatech!prism!ce1zzes ARPA: ce1zzes@prism.gatech.edu -- ERIC SHEPPARD Georgia Institute of Technology, Atlanta Georgia, 30332 uucp: ...!{allegra,amd,hplabs,seismo,ut-ngp}!gatech!prism!ce1zzes ARPA: ce1zzes@prism.gatech.edu