Is there something weird about PAL modems?

[kazade]

I've had no luck building a Dc-Pc server with my PAL modem (see my other thread), but while I've been searching around I've seen a pattern of posts which seem to show that even with a line voltage inducer, the PAL modem is extremely picky about which USB modems it will communicate with. This thread shows my exact problem: http://www.dreamcast-scene.com/communit ... =33&t=4343 I've seen other threads like this, and also one where changing the USB modem solved the problem.

The modem I'm using is a common Conexant one with two square green lights on the top, I've seen people using this modem successfully which makes me think that actually there is something different about PAL DC modems.

Has anyone figured out why some modems work and some don't? Is there something obviously different with PAL modems?

[DR TEAMCAST]

So I tried on my desktop computer that uses Ubuntu 10.04 and an old PCI modem

so I used drivers from linuxant which are supposed to do all the work

I think those two things are where you're going wrong. A.) What brourke told me was vm software doesnt like pci modems because they dont virtualize properly. B.) Linuxant drivers are pretty outdated and i think the developers don't support it anymore. You're better off assigning your modem to the com port that its using in windows


Also try to see if your voltage is setup right. No carrier is what happens when theres no voltage and the packets can't be transfered in time before timeout

[kazade]

To clarify, the post at that link isn't mine, it's just an example of what I keep seeing around the web - PAL modems not connecting to apparently supported modems despite a line voltage inducer.

I'm using a USB modem connected to a Raspberry Pi, running Linux directly (nothing is virtualized, I don't use Windows). I have a line voltage inducer with a 330 Ohm resistor and a 0.47mf capacitor and still it doesn't work.

I've posted on electronics.stackexchange.com to see if anyone knows why dialling with a phone is different than dialling with the DC modem.

Next week I'll have access to an oscilloscope, so if I make no progress before then I'll be able to debug this.

[DR TEAMCAST]

I'm using a USB modem connected to a Raspberry Pi

Ah i have no experience with pi-dc. The better question is how did you install the linuxant drivers to the ARM chip lol

You could try using vmware/virtualbox on pc with linux or windows 98 to see if it works. Then you'll know if its the modem or the pi configuration

[kazade]

OK, something seriously weird is going on. After a week of experimenting, I'm still unable to get my Dreamcast modem to work with a DC-PC server.

Here's what I've done.

1. Built several versions of a line voltage inducer, one with 9v + 330R resistor (27mA current), one with 12v + 330R (36mA), one with 9v + 470R (19mA) and one with 12v + 470R (24mA). Also tried both 0.47uf and 1uf capacitors.

I've tested these combinations to see what happens to the key tones from the Dreamcast with different power on the line (I read that BT uses 40mA, other sources recommend 24mA so I've tried everything).

2. The USB modem I'm using works perfectly fine with all versions of the LVI. I've tested by connecting a telephone to one end, through the LVI to the USB modem. The modem successfully receives the DTMF tones from the phone.

3. I've connected the Dreamcast to the telephone, and listed to the DTMF (key) tones through the phone. With all 9v versions of the LVI I can hear the dial tones clearly, with the 12v versions they are there, but barely audible. Either way, the Dreamcast is dialling and it's travelling along the line.

4. The USB modem won't respond to the Dreamcast modem. Nothing happens. Yet I've confirmed everything is working from both ends.

Has anyone seen this before? Any ideas what the solution could be?

[dude2207]

Quick idea here, If I remember right PAL Dreamcasts had 33K modems or something of that sort, not 56K modems. The speed difference may be causing issues.