XPR8400 repeater used for a SCADA link

[gohabs]

I am upgrading an old UHF analog MICOR repeater that is used as a SCADA hub that polls five remote pumping stations using modem controls, to an XPR8400. The hub radio is configured as a base station, not a repeater to disable the COR, and the modem provides PTT, and mic audio. The problem encountered is when the XPR is put in service, comms with the two closest pumping stations drops, but the more distant stations work fine, removing RF path as an issue. Thinking perhaps that there is a timing issue with the near sites, delay was inserted at the local modems. Also all audio compensation in the XPR such as de and pre-emphasis has been removed, with no luck. Anyone with any experience or ideas would be greatly appreciated.

[Wiregeek]

First thing that pops to mind is narrowband / wideband - what radios are at the pumping stations, and are they narrowband?

[gohabs]

All units are 25k. I was able to get some help from the SCADA software developer. We were able to look at data handshakes, and noticed that the two troubles stations were receiving the poll from the hub unit, but the return packet was missing data. The two closest stations that would not communicate with the XPR were CM200 uhf mobiles, the more distant stations used older M1225 mobiles. So on a whim I tried replacing the two CMs with spare M1225s and oddly enough they immediately started communicating with the XPR hub repeater. All the units have basic carrier squelch and no audio enhancing. Except for looking at the spec sheets of these two , I am at a loss why the older M1225 mobile will work for this app. and the newer CM unit will not.

[Bill_G]

Key up attack times. The M1225 is faster.

Or deviation. The M1225's are aligned and the CM200's are not, or they are set for narrowband.

[RFguy]

Older radios have little audio processing where new radios have a lot more audio processing/shaping and it's effecting the encode/decode of the FSK signalling?

[Bill_G]

Older radios have little audio processing where new radios have a lot more audio processing/shaping and it's effecting the encode/decode of the FSK signalling?

You could be right. He is using an XPR for a base, but the CM200 may be doing something to corrupt the envelope. Without looking at it with a scope, it's hard to say.