# \[LimeSDR-USB\] Tx Calibration: MCU error 5 (Loopback signal weak: not connected/insufficient gain?)

**URL:** <https://discourse.myriadrf.org/t/limesdr-usb-tx-calibration-mcu-error-5-loopback-signal-weak-not-connected-insufficient-gain/3323>\
**Category:** LimeSDR\
**Created:** [14 September 2018 23:13 UTC](https://discourse.myriadrf.org/t/limesdr-usb-tx-calibration-mcu-error-5-loopback-signal-weak-not-connected-insufficient-gain/3323 "2018-09-14T23:13:09Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![glados](https://avatars.discourse-cdn.com/v4/letter/g/74df32/32.png) [@glados](https://discourse.myriadrf.org/u/glados)\
**Post date:** [14 September 2018 23:13 UTC](https://discourse.myriadrf.org/t/limesdr-usb-tx-calibration-mcu-error-5-loopback-signal-weak-not-connected-insufficient-gain/3323/1 "2018-09-14T23:13:09Z")

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I am able to capture data from Rx, but when I use Tx, I got  
`Tx Calibration: MCU error 5 (Loopback signal weak: not connected/insufficient gain?)`  
Tried almost all solutions on the forum but the problem still cannot be solved, could someone help me fix it? Thanks!  
my software version is 18.06.1-PothosSDR-2018.09.09-vc14-x64 (latest version)