osmo-trx-lms: low tx output power level
According to https://discourse.myriadrf.org/t/limesdr-s-maximum-transmitting-power-at-different-frequencies/1649 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?
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 about 1 month 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.
- 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.
- Assignee changed from pespin to roh