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CSD modem connection issues

artyb Mar 19, 2020 04:44 AM


Firstly, I know that the days of landlines and CSD are both numbered, but we have existing systems using this comms route.

We have a few sites that we’re struggling to connect to, via a landline analogue modem to CSD cellular modems. One of our clients is able to connect to the sites. I’ve tried different modems, with some improvement.

Do you have any insight/advice as to why different modems may perform better than others, and what we could do to improve this? It shouldn’t be down to remote signal strength as our client can connect. Might it be down to serial data timing and autobauding?

On one site in a different country we are still having issues. We can mostly conenct to the modem, but apparently not to the logger. The Low Level Log shows:

..CONNECT 9600..











This looks to me as though LoggerNet is sending a connect/hello but not getting a reply from the logger. Is that right?

Is there any documentation on these autobauding and commands sent (eg the q and ' seen in the logs)?

Would you recommend not using autobauding?

We usually set the default logger baud rate to match the modem, but allow auto bauding so that eg a laptop can connect at a faster rate on a site visit. I'm wondering if the autobauding from the ring isn't working, and the logger is moving to a different baud rate?

It's odd that our client can connect from the same country though. Maybe different telecoms operators have different equipment routing the signal which makes the difference?

Thank you,


JDavis Mar 20, 2020 03:29 PM

Using fixed baud rates is definitely recommended. If the connection works from the other office, the baud rates on the equipment in the field is not the issue.

The likely culprits are:

Quality of landline at the office

PC modem used

Modem dial string used in Loggernet

artyb Mar 23, 2020 06:37 AM


Thanks for the reply. Can you tell me what the dots and q in the logs mean?

Any recommendations for PC modem?

Can you elaborate about the modem dial string in loggernet? Are there some options I could try?

I was wondering if the remote autobauding between logger attached modem could be thrown off if the signal from our line is distorted?

Best Wishes,


JDavis Mar 23, 2020 10:39 AM

The dots represent unprintable characters.

When the dial string entry box in Setup has focus(cursor inside box) push F1 to open help. That will give you help on the dial string. You will need to check your modem manual to see which AT commands it supports.

The best PC modems we have seen are external modems built by US Robotics.It looks like the current model is USR5686G

artyb Mar 24, 2020 04:19 AM


What do the q and ' indicate?

Could you give me an example of dial strings that might improve unreliable comms? I think you're refering to the logger settings, rather than LoggerNet where the only settings I can see are by editing the modem database. I'd have to establish a connection or visit site to change the logger settings though...

We have mainly used USR (admittedly older ones ~15-20 years old now). They tell me that their circuitry hasn't changed, but maybe some components in our modems had degraded. I've recently had more success with a different (now discontinued) modem, except for this one site.



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