BladeRF x115 / YateBTS / Noise

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dodolah
Posts: 1
Joined: Mon Apr 06, 2015 10:09 am

BladeRF x115 / YateBTS / Noise

Post by dodolah »

Hello,

Could you please help me (or point me to the appropriate tools) to reduce the "noise" on the board... What is the best tool(s) to (re)calibrate the board.

Serial #: 13d7b32e83118203e3e6db0b04de23bf
VCTCXO DAC calibration: 0x91b1
FPGA size: 115 KLE
FPGA loaded: yes
USB bus: 4
USB address: 2
USB speed: SuperSpeed
Backend: libusb
Instance: 0

bladeRF> version

bladeRF-cli version: 1.1.2-git-0295340
libbladeRF version: 1.2.1-git-0295340

Firmware version: 1.8.0
FPGA version: 0.1.2




I run some tests using yatebts and the connection was very unstable...

===================================

mbts noise
noise RSSI is -13 dB wrt full scale
MS RSSI target is -50 dB wrt full scale

mbts rxgain
current RX gain is 0 dB


===================================

-13db is the minimum reachable on the board.

I tried to calibrate the board with "kalibrate-bladeRF", and it looks even worse.

./src/kal -s GSM850 -m4

Actual filter bandwidth = 1500 kHz
rxvga1 = 20 dB
rxvga2 = 30 dB
kal: Scanning for GSM-850 base stations.
GSM-850:
chan: 128 (869.2MHz - 1.362kHz) power: 35627.82
chan: 129 (869.4MHz - 1.349kHz) power: 37119.38
chan: 130 (869.6MHz - 1.382kHz) power: 37840.33

./src/kal -v -c 128
Found lowest offset of 264.594208Hz at 869.200000MHz (0.304411 ppm) using DAC trim 0x8fff

=====

Thank you,
andrew77
Posts: 29
Joined: Mon Mar 02, 2015 2:02 pm

Re: BladeRF x115 / YateBTS / Noise

Post by andrew77 »

Hello,
when you execute mbts noise and the result is:
noise RSSI is -13 dB wrt full scale
MS RSSI target is -50 dB wrt full scale

in my own experience it is because of the one of following things:
RX antenna not matched (not taylored for the band in use)
TX antenna too colse from the RXantenna
mbts rxgain set >0

I got the same your results in these cases,
but if you tray with a dummy load (50 ohm) on both RX and TX ports you get around -46 dB of noise RSSI (tray to set mbts rxgain =0)
for a well matched antenna I got around -30 dB of noise
avalori
Posts: 1
Joined: Mon Oct 19, 2020 7:51 am

Re: BladeRF x115 / YateBTS / Noise

Post by avalori »

Thanks for your post.
First of all it helped me to determine that a noise of -35 dB is not unusual on a bladeRF (although I have the x40 not the x115).
However, I am extremely puzzled by the stuff below bold for the main points.
I tried to run the noise command with rxgain as 75 and then after changing rxgain to 0.
What is puzzling is that the noise seems basically the same (-35 vs -34 dB).
Any ideas/suggestions?
Additionally, seems way higher than the recommended value by Yate ("Normal UL noise level is -64 or lower").
Indeed, I mange to have reasonable voice and SMS but horrible if any GPRS...

Many thanks in advance.


-----------------------------------------------------------------------------
mbts rawconfig rxgain 75
defined new config rxgain as "75"
mbts noise
noise RSSI is -35 dB wrt full scale
NOTE: Excessive UL noise will degrade performance. Normal UL noise level is -64 or lower.
MS GSM RSSI target is -50 dB wrt full scale
NOTE: GSM UL RSSI margin -15 too low for this noise level. Should raise GSM.Radio.RSSITarget to -27 dB or higher.
MS GPRS RSSI target is -25 dB wrt full scale
NOTE: GPRS UL RSSI margin 10 too low for this noise level. Should raise GPRS.MS.Power.RSSITarget to -21 dB or higher.
mbts rawconfig rxgain 0
rxgain changed from "75" to "0"
mbts noise
noise RSSI is -34 dB wrt full scale
NOTE: Excessive UL noise will degrade performance. Normal UL noise level is -64 or lower.
MS GSM RSSI target is -50 dB wrt full scale
NOTE: GSM UL RSSI margin -16 too low for this noise level. Should raise GSM.Radio.RSSITarget to -26 dB or higher.
MS GPRS RSSI target is -25 dB wrt full scale
NOTE: GPRS UL RSSI margin 9 too low for this noise level. Should raise GPRS.MS.Power.RSSITarget to -20 dB or higher.
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