Bug #3342

osmo-trx-lms: low tx output power level

Added by laforge 7 months ago. Updated about 2 months ago.

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According to I would expect something like 3-5dBm maximum output power at 1.8 GHz.

Hoewever, when running at ARFCN 871, and even when manually patching LMS_SetNormalizedGain(m_lms_dev, LMS_CH_TX, chan, 1.0); into the osmo-trx-lms source code, I'm not seeing more than -3.8 dB coming out of the TX1_1 port of the device. Where does that 6..8 dB difference come from?

Related issues

Related to OsmoTRX - Feature #2919: Native LimeSDR supportResolved2018-02-09


#1 Updated by laforge 7 months ago

#2 Updated by duo_kali 4 months ago

Tested also with 900MHZ, seems the output power and rx gain using osmo-trx-lms is less compare using osmo-trx-uhd.

I dont have the spectum analyzer here, but testing many times and compare using phone to camp and call with osmo-trx-uhd has produce more power than osmo-trx-lms, so automatically using UHD increase range coverage.

#3 Updated by Armin 2 months ago

Have the same issue with LimeSDR mini connected via USB3 to my host machine. LimeSDR mini producing only -12dBm RF power tuned and transmitting my GSM network on 935.0 MHz.
When I used LimeSuite to transmit CW on max possible power setting, I got 13.2 dBm on 935 MHz.
I tried also to play with some config parameters of osmo-bts, like

user-gain Inform BTS about additional, user-provided gain or attenuation at TRX output
power-ramp Power-Ramp settingsMaximum initial power

but these parameters doesn't change anything.

#4 Updated by Armin 2 months ago

I was able to increase output power by using in osmo-trx-limesdr.cfg in trx section

tx-path BAND2

instead of BAND1

This increased power to 5 dBm.

#5 Updated by laforge about 2 months ago

  • Status changed from New to In Progress
  • Assignee set to pespin
  • % Done changed from 0 to 50

the output level is expected to be rather low (-5 dBm?). Lower levels were likely a result of using only 30% of the full 16bit sample scale (see #3341).

One remaining difficulty is to know which port (BAND1/BAND2) is ideal for a given transimt frequency. It seems that the LimeSDR-mini vs. LimeSDR-USB have inverted recommendations about which ports shall be used for which frequency. We've asked lime to provide a related table, so we can then in software at least print a warning if a user selects a sub-optimal combination.

#6 Updated by laforge about 2 months ago

  • Assignee changed from pespin to roh


roh please re-test using those changes, and without using any 'osmotrx tx-attenuation' in your config files

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