The Difference of Signal Strength From Two Channels on The Same Board is Big

jiangwy wyjiang at ljshuoda.com
Sat Aug 3 02:48:56 UTC 2013


Hi Andrey Sviyazov.

I have tried the kal program on both boards, the output are:

The following commands are executed on the normal board
./kal -s GSM900 -v -R A:0
kal: Scanning for GSM-900 base stations.
channel detect threshold: 19506.878626                                                               
        chan: 11 (937.2MHz - 13.389kHz) power: 53673.23                       
        chan: 14 (937.8MHz +   4Hz)     power: 64031.10                       
        chan: 16 (938.2MHz +  30Hz)     power: 37823.70                                             
        chan: 43 (943.6MHz +   2Hz)     power: 77249.29                                        
        chan: 50 (945.0MHz -  24Hz)     power: 29420.52                                             

./kal -s GSM900 -v -R B:0        
kal: Scanning for GSM-900 base stations.
channel detect threshold: 28406.616263                                                              
        chan: 11 (937.2MHz - 6.120kHz)  power: 53776.77                       
        chan: 14 (937.8MHz -  59Hz)     power: 76683.83                       
        chan: 16 (938.2MHz + 28.945kHz) power: 46724.84                                                                                          
        chan: 43 (943.6MHz + 38.130kHz) power: 65350.20                       
        chan: 50 (945.0MHz -  21Hz)     power: 29930.09           

The following commands are executed on another board seeming to be abnormal
./kal -s GSM900 -v -R A:0
kal: Scanning for GSM-900 base stations.
channel detect threshold: 4486.504362                                         
        chan: 5 (936.0MHz -  15Hz)      power: 6734.70                        
        chan: 12 (937.4MHz +  50Hz)     power: 9339.20                                                
        chan: 83 (951.6MHz -  13Hz)     power: 6462.91          
        
./kal -s GSM900 -v -R B:0
kal: Scanning for GSM-900 base stations.
channel detect threshold: 27671.315417                                        
        chan: 5 (936.0MHz +  24Hz)      power: 29673.93                                           
        chan: 12 (937.4MHz +  40Hz)     power: 69096.60                                            
        chan: 83 (951.6MHz -   4Hz)     power: 46394.73                       

./kal -c 1004 -R A:0
kal: Calculating clock frequency offset.
Using E-GSM-900 channel 1004 (931.0MHz)
average         [min, max]      (range, stddev)
+   2Hz         [-80, 79]       (159, 44.543312)
overruns: 0
not found: 34

./kal -c 1004 -R B:0
kal: Calculating clock frequency offset.
Using E-GSM-900 channel 1004 (931.0MHz)
average         [min, max]      (range, stddev)
+   1Hz         [-13, 19]       (32, 8.658517)
overruns: 0
not found: 0  

Best Regards.




jiangwy

From: Andrey Sviyazov
Date: 2013-08-03 00:54
To: wyjiang
CC: UmTRX; Alexander Chemeris
Subject: Re: Re: The Difference of Signal Strength From Two Channels on The Same Board is Big
Hi Jiang Wenyi.


Please double check that both UmTRX's runs with the same FPGA images (and firmware).
If absolutely the same then seems one board is broken.
Please double check it also by some other tests to be sure before send to us for repair.


Best regards,
Andrey Sviyazov.



2013/8/2 jiangwy <wyjiang at ljshuoda.com>

I try another UmTRX board, and it's OK. The difference from the channel 0 and 1 is very small.




jiangwy

From: Alexander Chemeris
Date: 2013-08-02 17:30
To: wyjiang
CC: UmTRX
Subject: Re: Re: The Difference of Signal Strength From Two Channels on The Same Board is Big
Ok.

Also check that a correct input is selected on both chips
(--lms-get-rx-lna option).

Then, could you check whether this is consistent among both UmTRX you have?

On Fri, Aug 2, 2013 at 12:55 PM, jiangwy <wyjiang at ljshuoda.com> wrote:
> I use the following command
>
> ./umtrx_lms.py --lms {1,2} --lms-get-rx-vga2-gain
>
> the outputs are all the same ( 15 ).
>
> ________________________________
> jiangwy
>
> From: Alexander Chemeris
> Date: 2013-08-02 16:20
> To: wyjiang
> CC: UmTRX
> Subject: Re: The Difference of Signal Strength From Two Channels on The Same
> Board is Big
> Hi Jiang,
>
> Are you sure you're setting Rx gain properly for both channels?
> I recommend you to use umtrx_lms.py script from this repository to
> check Rx LNA and Rx VGA settings for both LMS chips:
> https://github.com/fairwaves/umtrx_scripts
>
> On Fri, Aug 2, 2013 at 12:09 PM, jiangwy <wyjiang at ljshuoda.com> wrote:
>> Hi Alexander Chemeris,
>>
>> According to rx_multi_samples , I write a program to receive samples from
>> two channels on the same board.
>> The program receive samples from 2 channels and calculate the signal
>> strength respectively. The signal is from a BTS arround.
>> I find the difference of signal strength is very big, about 20dB, and
>> channel 1 is bigger than channel 0.
>> I  exchange the antenna and feeder of the them, but the result is same.
>> I think there is some problem, but I cann't find it.
>> Would you please give me some sugguestion?
>>
>> Best Regards.
>>
>> ________________________________
>> Jiang Wenyi
>
>
>
> --
> Regards,
> Alexander Chemeris.
> CEO, Fairwaves LLC / ООО УмРадио
> http://fairwaves.ru
>



-- 
Regards,
Alexander Chemeris.
CEO, Fairwaves LLC / ООО УмРадио
http://fairwaves.ru
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