LimeSDR Mini V1.1 RX1_W input issue

General Discussion
1

I bought the original Mini on CrowdSupply but have hardly used it since. In fact, I mostly only got as far as listening to broadcast FM.

I now have a project to use it seriously (< 100Mhz) and first thing I did was run the LimeQuickTest (LimeSuiteVersion 23.11.0-1) and getting a failure on loopback. This seems to be a recurring problem but it appears there are two scenarios: 1) slightly out of tolerance due to temperature; and 2) significantly out of tolerance. Unfortunately, mine is the latter:

[ RF Loopback Test ]
->Configure LMS
->Run Tests (TX_2 -> LNA_W):
  CH0 (SXR=1000.0MHz, SXT=1005.0MHz): Result:(-55.6 dBFS, 5.00 MHz) - FAILED
->Run Tests (TX_1 -> LNA_H):
  CH0 (SXR=2100.0MHz, SXT=2105.0MHz): Result:(-20.7 dBFS, 5.00 MHz) - PASSED
->RF Loopback Test FAILED

This is backed up by general reception being about 15dbm or more lower than the same setup and circumstances as my LimeNet Micro.

Tracing the signal through, I found that the DC input resistance (not powered and no signal connected) on rfgp_w_RFE_1 (pin AN9) is only 33 ohms, whereas the other input rfgn_w_RFE_1 (pin AP10) is 120kohms. The high band inputs are (RX1_H) are 10Mohms.

Curiously, the input does still work, but I suspect it is unbalanced on the ‘n’ input only and therefore half the expected power.

There seem to be a few other people with -50ish dBFS loopbacks, so was this a manufacturing issue, or has something simply failed?

Is the only remedy to replace the LMS7002 or is it a known problem with this board issue that can be fixed?

I was thinking to take the caps off the RX1_W input and fit them to the RX1_H input but it is a fiddle as I only have limited equipment and skills.

Buying a Mini 2.0 at $399 doesn’t seem that attractive right now.

2

We’re not aware of any such manufacturing issue and every board goes through production test after assembly. We’ve also had very few RMAs out of many thousands of boards shipped, and I’m pretty sure we would have heard from one of the volume customers — some purchase hundreds at a time — if there were reliability issues.

I’ll ask colleagues. Presumably you could use LNA_H for now?

3

Thank you for the reply.

Presumably you could use LNA_H for now?

The problem is I am using frequencies sub-100MHz and the performance using LNA_H is degraded at those frequencies due to the input filter.

I also have a LimeNet Micro whose performance is excellent which I can use for proof-of-concept, but I need the smaller former factor of the Mini for this project.