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Bug #4637

limesdr usb gain setting changes break gsm phasenoise constraints

Added by roh 5 days ago.

Status:
New
Priority:
Normal
Assignee:
-
Category:
LimeSDR
Target version:
-
Start date:
06/29/2020
Due date:
% Done:

0%

Spec Reference:

Description

i tested limesdr usb today to validate the latest patches (proper tx power correlation #4583)

the gain calculation is fine in general, but i get a bit less power than expected on 1800 now.
its 65dB txgain and -5.2dBm power output.... not sure if i measured wrong the last time or what has happened.
all the other values were as expected.

sadly i get a lot of phase-errors now, which i assume have to do with ramping being active by default now? from my pov one cannot do ramping at all with a limesdr hardware in general atm.

all the filters need to be recalibrated for every frequency, bandwidth and power setting. this generates rf noise and is only done once on powerup.
simply changing the gain is not not good enough on this hardware.

debugdump:
Library version: v20.01.0-1
Build timestamp: 2020-01-29
Interface version: v2020.1.0
Binary interface: 20.01-1
Device name: LimeSDR-USB
Expansion name: UNSUPPORTED
Firmware version: 4
Hardware version: 4
Protocol version: 1
Gateware version: 2
Gateware revision: 22
Gateware target: LimeSDR-USB
Serial number: 0x90726074d341c
Free connection... OK
OsmoBSC version 1.6.0.159-68b775
OsmoBTS version 1.2.0.162-f23d
OsmoTRX version 1.2.0.48-f68f1

connection via usb3 from apu2 board.

from my pov lime support is broken as long as there are any calls using LMS_SetGaindB and tx which are not combined with the full filter and calibration calls.

since those need to happen before streaming is enabled (afaik) this is difficult to do, and one would need to do a full 'ramp' on powerup, cache all the filter and calibration-values from the registers (basically set gain, bw, freq, then dump registers) and re-use these values lateron when a specific gain is requested.

i'd like to disable any ramping on this platform till this is fixed (if possible)

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