Quick Start Signals on viewer different levels

I’m trying to get the quick start to work. I’ve run this on windows and linux with same results. The blue trace (receiving?) is significantly lower.

Could you tell us which versions you are running of:

  • Lime Suite
  • Firmware
  • Gateware

INFO: Connected Control port: LimeSDR-USB FW:4 HW:4 Protocol:1 GW:2 GW_rev:12 Ref Clk: 30.72 MHz
Version information:
Library version: v17.12.0-myriadrf~xenial
Build timestamp: 2017-12-13
Interface version: v2017.12.0
Binary interface: 17.12-1


Make sure that you check “MIMO” box when uploading waveform and enable loopback for both channels (A and B) in board settings. If those things are set correctly then probably some part(s) of second channel on your boards is bad/damaged.

I did double check and I do have both A&B loop back checked. If I don’t select loop back B, then the blue trace increase slightly.I did not see anything that looked broken physically on the board. But determining bad parts can be more troublesome.

I’ll see if I can find anything looking at the control signals. Do you think these transmit paths will work down at 1.7GHz? I think I have an old SA that works to 1.8G

All the control signals seem to get to caps at the control devices. I’ll see if I can find the bits to do an external loop back or try to reduce the frequency so I can check it out with a spectrum analyzer. I’m guessing the transmitter for the B loop is not working and the signal I see is a leakage signal from the A loop.

@zack do you have any other suggestions?

manual external loop back with approximately 34dB attenuation. Followed Quick Test and then removed internal loop back using board controls.
Tx1_2 -> Rx2_H

Tx1_2 -> Rx1_H

Tx2_2 -> Rx1_H

Tx2_2 -> Rx2_H

Looks like about a 10dB+ difference in receivers and Tx2_2 seems like it might not be transmitting.

I seem to have similar discrepancy. I tracked 10dB loss to one line of differential pair of LNAW (if i remember correctly ) to be unresponsive. Probably LMS7002D soldering issue or damaged IC. Other channels are fine(LNAL LNAH). I contacted LimeSDR due this defect lung time ago but no response at all so far. I used external cables and power splitter.

@dooble Take a look at the TCM1-63AX issue posted before, but be very careful touching T7 :slight_smile:

I looked at the transformer under the magnification I have available and buzzed it out with not luck. DC measurements on an RF transformer are often fruitless. I’ll need to get some soldering supplies and better magnification before I tackle this.

@cc68 thank you for the tip!

Now that I’m back in country, I did a little more investigation. Using an external feedback I found that Rx1_H has about 10dB more gain than Rx2_H. I also found that Tx2_2 has a flaky transformer (T7). This intermittently worked, but is damaged. When working Tx2_2 and Tx1_2 had approximately the same levels (using external loop back). I just used the the quick start and disabled loopback. I used the fft viewer to measure levels.

I’m not sure the best way to remove the transformers without disturbing the rest of the circuit. I’ve got a single iron and a few hot air tools. Still have to sort the receiver difference. I wonder what testing was done on these units before shipment.

@dooble - James,

I’ve seen this issue, too…I own two V1.4 LimeSDRs (one I purchased from the Early Bird, one I purchased later from another Ham getting out of LimeSDR). The one I purchased from the Ham that had it modified for HF from Crowdsupply and I’m finding that this SDR has poor receive on HF, but strangely it’s good on VHF to SHF but I can clearly see the mod was done (coils were removed that match the transformers for Cell and WiFi). I have to attribute this to ‘cracked balls’ on the 7002 BGA that are allowing better connection at higher frequencies than lower frequencies. And as others have also offered, this is not a first occurrence. One LimeSDR user had his 7002 come completely off the card after it fell off a desk, but there was a heatsink applied, too, that may have also contributed to the shearing that happened on that.

Anyway, it’s just an observation, but I’m seeing it too on my second board, but my first one is bullet-proof…Works like a charm.

73 de Marty, KN0CK

thanks. I got the transformer off with hot air. Disturbed a matching cap. I have placed it back in its place.

My board was a pre-order too.

This still does not solve the receiver differences. The idea of cracked balls is not a good thing. Very little I can do with that. I’ll get some transformers and see if that fixes Tx2_2. Next will be to check out the rest of the TX/RX


@dooble - James,

It’s a theory only (cracked balls), but it surprised me that the second Lime I purchased from a later batch (my first one was an ‘Early Bird’ Lime and works everywhere) had decent receive at and above the FM band but was pretty much lacking below 30 MHz and was an HF-modified Lime. I have a better signal generator now and can run some more definitive testing on that suspect Lime to see what the real receive sensitivity is in the HF band…Stay tuned on that…

73 de Marty, KN0CK

@andrewback, it looks like the flaky Tx2_2 is due to a not stable transformer. I have this part off and will order another to see if that fixes it. The 10dB difference is likely 12dB in reality and as @modimo suggests is likely a solder problem on the lime chip. 12dB would likely be correct for one differential line not being connected if my maths are not faulty. I have the capability to pop of a transformer. I do not have the capability to pop off, reball and place a BGA part in my home. This sounds like an assembly issue. Was this tested at manufacture?

Indeed, all boards are put though comprehensive testing after manufacture. I guess it’s possible that damage could occur during shipping. Out of the many thousands made, we’ve only had a very small number returned.

The LMS7002M is a QFN and not BGA. The FPGA is BGA, but this obviously doesn’t connect to the transformers.

@andrewback Any suggestions what to do? Is there any warranty for the boards?

Yes, provided you haven’t modified the board in any way, an RMA should be arranged via Crowd Supply if upon receipt it fails the quick test.

@andrewback, I think that leaves me out as I removed (yesterday) the Tx2_2 transformer because it was an obvious problem. I did nothing other than connect RF cables so I could do external loop back. I had assumed from the lack of followup from the earlier comments that I was on my own.

QFN’s can get no solders or intermittent connections, but less likely. If I recall this is an odd QFN with many signal pads not on the edge. I’ve never worked with these packages. I would expect these to be difficult to remove/replace.

I’ll see what else might work with this one. thanks for the reply

One suggestion of packaging. Use a larger ESD bag. The one I received with my unit is very tight when removing/inserting the LimeSDR. It is possible that the bag size could cause damage to the transformers near the edge of the board on the long edges.

Well I did solder pins for fan supply. Does that mean my warranty is void?