[Imported] Troubleshooting problems on a radio system


[Imported] Troubleshooting problems on a radio system

>>Message imported from previous forum - Category:Trio Data Radios<<
User: joelw, originally posted: 2018-10-16 21:38:36 Id:32
This is a re-posting from the obsoleted (October 2018) "Schneider Electric Telemetry & SCADA" forum.


When looking for the source of poor or intermittent communication in a radio system, there are many potential failure sources. Here are a few suggestions for how to proceed when the problem isn't something you can solve quickly. Feel free to hit Reply and post some of your own suggestions!_**


Do you know how to use TView+ Diagnostics? Make sure you do (and that you have a copy installed) before you go to site! Run it to poll all the radios from the Master site. Look for high VSWR, low power supply voltage, incorrectly programmed Tx power etc.

Record the RSSI (received signal strength indication) for every remote site. Compare that against the radio's Rx sensitivity. (See the list at the bottom for sensitivity for all Trio models) All paths should have 20 dB of fade margin or more. Eg if K Series radios are programmed for 32 kbps radio data rate they have -108 dBm sensitivity. To have 20 dB fade margin each path would need -88 dBm RSSI or higher. (This may need to be higher if the local noise floor is stronger than the radio's receive sensitivity)

If fade margins at some sites are significantly below 20 dB, reduce the radio data rate (in ALL radios!) to 32 kbps (K Series) if not already there and if the user application allows it. (or 256 kbps instead of 512 kbps in J Series)
Check the antenna aiming for installation errors. Take a compass (with declination properly set!) and check aiming against the path study recommendation, if a study was done.

If antenna aiming is suspected as a problem, poll the radio (eg Individual Poll) while it's listening to its Master. Or if there's no radio traffic at the time poll the Master from the remote to cause traffic. Slowly move the Yagi antenna left/right to see if signal can be improved. (note that Individual Poll only updates every 2 seconds, so move the antenna a bit then wait for it to update)

If VSWR at any site is high (above 2 is a concern, but above 3 is a real problem) look for a damaged or incorrect type antenna, damaged or incorrect coax (must be 50 ohm type), damaged, loose or improperly installed connectors, or a bad surge arrestor. (polyphaser) This may require swapping out the antenna or coax (including jumper from radio to polyphaser) with a known good replacement.

Get permission to shut the system down for a few minutes (if possible) then run the spectrum analyzer at the Master. (If K or J Series) Look for any nearby strong signals that might be causing interference. Eg some cell towers are in the 850 MHz band and can cause problems if very near, and some paging systems are in the 950 range. A bandpass filter can be purchased and installed at the site near the interference source.

Run the spectrum analyzer at the most problematic remote sites. The master won't stop transmitting though, so you'll see some of its transmissions as it hops around. But still usually it's fairly apparent if there's a lot of interference or if the noise floor is higher than normal. If possible power down the Master while doing this to avoid seeing its transmissions.
Make sure the Master antenna is high and in the clear, and that the VSWR is low when running diagnostics. (VSWR for all sites should be under 2)

Was a path study done to calculate antenna heights or were they guessing? If no study was done, it might be necessary to do one or to modify antenna heights or types and/or convert some sites to Bridges.

Try bypassing the polyphaser at each site, most importantly at the Master. You may need a double-female adapter to tie the two cables together, or another polyphaser would of course work. These devices do become very lossy if they have absorbed lightning strikes or nearby surges.

Check all external coax cable connections to ensure they are thoroughly waterproofed. Water in a coaxial cable will cause power loss and seemingly low (not high!) VSWR.

At the remote sites, look for obstacles nearby in the path towards the Master. Eg a lot of trees nearby or a metal building. The antenna may need to be moved up to reduce losses. An additional 5-10 feet is often enough though on some obstructed paths the RSSI might actually get worse. In such a case try moving the antenna even further up, or in some cases moving it below the original height might help.

Do you know the protocol being used? Check the serial port config at each site to ensure the correct packet layer is chosen, especially if it's Modbus!

Check all communication cables to ensure nothing's loose and that they are the correct type. Also look for high voltage cables nearby that could induce hum on comms cables.

Don't forget to check the power supplies, as always! K Series needs 12-24 volts approximately, and the output should stay steady even while transmitting & drawing about 500 mA at 12 volts.

If a path remains weak a path study may need to be done to calculate a required antenna height. To do this make sure you have accurate GPS coordinates for all sites involved, note accurate tree heights and other obstacles near any of the sites. Fill out the path study request form, found on the Control Microsystems website (completely!!) then send it to TRSSpathstudy[at]schneider-electric.com.

Alternately you may reconfigure a nearby Remote as a Bridge (store & forward repeater) and aim the problem site's antenna at that site. This would require either changing the antenna at the Bridge site to an omni (if its path is strong enough to handle the 5+ dB reduction in signal strength this will cause) or an omni may be added to the ANT2 port and the Bridge set to Dual Antenna mode. (If J or K Series) In some cases where two sites are very close (eg under 1 km and no big obstacles between them) the Bridge may pick up the Remote's signal off the back or side of its yagi.


Re: [Imported] Troubleshooting problems on a radio system

>>Responses imported from previous forum

Reply From User: joelw, posted: 2018-10-16 21:38:48
Receiver sensitivity for Trio radio models:

K Series
256 kbps -102 dBm
128 kbps -104 dBm
64 kbps -106 dBm
32 kbps -108 dBm

J Series
512 kbps -92 dBm
256 kbps -102 dBm

E Series
9600 bps -108 dBm
19k2 -96 dBm 12.5 kHz radio
19k2 -106 dBm 25 kHz radio (not approved for North America)

M Series
9600 bps -106 dBm

Joel A. Weder
SCADA & Telemetry Solutions Specialist
Schneider Electric