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VIP Member
Reputation: 1716
RSSI Troubleshooting with Dummy load
Hello people
I have question about RSSI troubleshooting. concretely in Huawei CDMA2000 450mHz network.
So some BTS have RSSI problem - Div RSSI Average Value [dBm] - -97.6 / Main RSSI Average Value [dBm] - -64.
So my question is to exclude the board problem on these BTS. I have read in some docs that using the dummy load can help on this issue - to connect dummy load on the TRX board [on the main] and monitoring the RSSI.
Is it correct to use dummy load to exclude board problem? And has anyone more information about this problem or any some RSSI troubleshooting documents?
Thanks
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2011-11-17 10:56 PM
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VIP Member
Reputation: 2736
Re: RSSI Troubleshooting with Dummy load
Hi. I had a problem with Huawei. Vendor mounted with equipment not quality antenna. When you turn on three carriers appeared intermodulation.
In order to check the quality of the antenna turn off the transmitter. If the RSSI will be normal - to replace the antenna.
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Re: RSSI Troubleshooting with Dummy load
Originally Posted by
DANCESTORM
Hello people
I have question about RSSI troubleshooting. concretely in Huawei CDMA2000 450mHz network.
So some BTS have RSSI problem - Div RSSI Average Value [dBm] - -97.6 / Main RSSI Average Value [dBm] - -64.
So my question is to exclude the board problem on these BTS. I have read in some docs that using the dummy load can help on this issue - to connect dummy load on the TRX board [on the main] and monitoring the RSSI.
Is it correct to use dummy load to exclude board problem? And has anyone more information about this problem or any some RSSI troubleshooting documents?
Thanks
Hi DANCESTORM, using dummy loads may give you inaccurate results and therefore confuse you. If you want to isolate HW, then just replace it with a spare card. That would instantly verify your HW.
Usually high RSSI (>-95dBm) is caused by very heavy cell loading or simply RF interference.
So:
1. verify HW if you want or suspect. (I usually wouldn't)
2. check what times do you have high rssi. is only peak times (indicates heavy loading, check stats) or certain periods (indicates RFI at distinct times, most probably therefore external interference from some other source). Is the RFI in 1 BTS or a number of neighboring BTSs (indicates external interference if in more than 1 BTSs & neighbor BTSs)
3. use these commands (for 6600, for 6680 should be something similar and not hard to find in command list) STR CBTSRVSITFERMNIT & STR CBTSRVSWITFERMNIT. Collect data stored in D:\Airbridge\services\BTSRVSITFER\ and D:\Airbridge\services\BTSITFLOG\ respectively and analyse using NASTAR.
It will clearly show if RFI exists.
4. If RFI is external, then it could require some work to find the source of RFI. Usually you'll need a spectrum analyser and a directional antenna.
Last edited by T_ADD; 2011-11-19 at 09:15 AM
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VIP Member
Reputation: 1716
Re: RSSI Troubleshooting with Dummy load
Originally Posted by
hactic
Hi DANCESTORM, using dummy loads may give you inaccurate results and therefore confuse you. If you want to isolate HW, then just replace it with a spare card. That would instantly verify your HW.
Usually high RSSI (>-95dBm) is caused by very heavy cell loading or simply RF interference.
So:
1. verify HW if you want or suspect. (I usually wouldn't)
2. check what times do you have high rssi. is only peak times (indicates heavy loading, check stats) or certain periods (indicates RFI at distinct times, most probably therefore external interference from some other source). Is the RFI in 1 BTS or a number of neighboring BTSs (indicates external interference if in more than 1 BTSs & neighbor BTSs)
3. use these commands (for 6600, for 6680 should be something similar and not hard to find in command list) STR CBTSRVSITFERMNIT & STR CBTSRVSWITFERMNIT. Collect data stored in D:\Airbridge\services\BTSRVSITFER\ and D:\Airbridge\services\BTSITFLOG\ respectively and analyse using NASTAR.
It will clearly show if RFI exists.
4. If RFI is external, then it could require some work to find the source of RFI. Usually you'll need a spectrum analyser and a directional antenna.
Hactic as i have read the idea of using dummy load (connecting on the Main connector) is to exclude antenna/feeder system and find board internal problem. So the dummy load is just attenuation, that not to damage transmitter. We know that there is "RF tract" form amplifier to transmitter, and in some situation there can be some problem. So when we connecting dummy load, there will form like "loop", so if this RF tract is damaged the reflected wave will come back and thats affects on RSSI.
And what about your suggestion about replacing the board its too hard, need too much time and also the service will be interupted.
On some site RSSI is every time big difference between Main and DIV. this can be external interference and antenna/feeder problem. Ecxlude antenna/feeder problem by sitemaster, external interference by spectrum analyzer. So left HW, but do also need check.
And my nastar not working i don't exactly why. :s
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Member
Reputation: 62
Re: RSSI Troubleshooting with Dummy load
On some site RSSI is every time big difference between Main and DIV. this can be external interference and antenna/feeder problem.
With big difference between main and div intermodulation is suspected. It's easy to check - change tx power and observe interference - when it changes along with tx power change it's intermodulation probably due to corrosion somewhere in the system. Sometimes intermodulation is external - it reacts to the antenna tilt change then.
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VIP Member
Reputation: 1716
Re: RSSI Troubleshooting with Dummy load
Originally Posted by
dremka
On some site RSSI is every time big difference between Main and DIV. this can be external interference and antenna/feeder problem.
With big difference between main and div intermodulation is suspected. It's easy to check - change tx power and observe interference - when it changes along with tx power change it's intermodulation probably due to corrosion somewhere in the system. Sometimes intermodulation is external - it reacts to the antenna tilt change then.
do you have more info about intermodulation? or you can write here more clearly
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