LimeNET Micro impressions

[adim]

So, I finally managed to squeeze enough time to buy and test the LimeNET Micro, something I was eyeing since last summer.

First impressions are very good, it clearly has a lot more features than the LimeSDR-mini, and I was very impressed to see the software stack (LimeSuite) working very well and all the troubles I had with my mini pre-release board now completely gone. Congrats to the Lime developers.

I am using the board in USB mode for now, through SoapySDR (because I’m too lazy to add gr-limesdr sources and sinks to qradiolink at the moment). If and when I start working with a DMR software stack, I’ll probably have to switch to gr-limesdr to make use of the tx_time tags. But Soapy has been flawless so far.

Radio-wise, don’t expect to be able to use the board without band filters. Adding band-pass filters for the desired band makes a huge difference on reception. On the 430 MHz band, where I want to use this board as a standalone mixed mode repeater, the LimeNet Micro was a bit more deaf than the Pluto I also use. It is less prone to interference from Wifi than the Pluto, on the other hand I think I have some faint 3G images in the band.
What I haven’t been able to do was find the ideal RX gain settings for the various stages. Like the mini board, the documentation on the wiki is a bit patchy, finding it necessary sometimes to go dig through the source of LimeSuite to find out things.
It would be very nice to have a reference for good known settings for the gain stages somewhere.
On the other hand, I did not fire up my PGA-103+ LNA yet, and the signal levels are adequate if not stellar. I expect the LNA to improve reception.

Transmission is ok on the 70 cm band, the power level is good but you need to be careful to set TX gain to maximum before activating the TX side of the board, otherwise the MCU complains that it can’t calibrate TX. After the calibration is done (which now is very fast compared to the mini dev board I had), you can programatically reduce TX gain to minimum.
The automatic RX and TX path selection is a huge improvement, I don’t have to worry about setting it as I sweep the frequency across bands.
I noticed quite a bit of LO leakage on duplex TX, but I can’t tell what is the expected level of LO leakage after calibration. It would be helpful to have this information somewhere.

My board did not come with Wifi, or at least it does not have the connector soldered. This is something I fault the distributor for, as they did not specify this in the description. Be careful if you want this feature.

I am eagerly expecting the general availability of LimeRFE, since that is something that my project needs. If it works as well as the LimeNet Micro, then us amateurs experimenting on VHF to SHF frequencies will have a big winner on our hands.

Best regards,
Adrian

[9a4db]

Hi Adrian,
guess you missed nice discussion with Andrew and Zack about
configuration of CrowdSupply LimeNET micro in campaign.

The LimeNET Micro campaign is live!

Just to notice that I finally opened my LimeNET Micro on intention to prepare proper case and cooling. It is so called early bird board and on my surprise it is BOM_VER 1 (R34 NF) according to: https://wiki.myriadrf.org/LimeNET-Micro_v2.1_hardware_description that means -> SDR (without duplexers and WiFi module) For my needs WiFi is not necessary but duplexers may be useful. Any way can not remember that early bird boards was expected to be crippled on major RF side…

Any way I find nice use for my board after some considerations what to do

Something I nicknamed LimeToGo… remote RX system using Soapy Remote.
Any way now have whole ICOM PCR-1000 like preselector and taking the signal at IF 10,7 MHz than go on up conversion (at the moment with MoRFeus) to 85 MHz - IF
Now just about to make mods for Virtual USB interface for GNSS Ublox M8 communication to CM3.
Final intention is to locate and monitor nearest available Galileo satellite for 1,5 GHz COSPAS-SARSAT SAR transponder.

BTW during my testing in direct USB mode was able to RX with LNA4HF lowest at 7 MHz and lowest TX signal was available at 21 MHz

Regards
Djani

[adim]

Djani, good to hear from you again, glad you’re having fun with the SDR. I have to say I want to do some work with GNU radio on the DMR stack because I’m already sortof familiar with the ETSI papers and I always wanted to learn more on turbo codes of the family used in DMR. The adoption of DMR is growing, and TDMA is an interesting concept which is worth exploring a little more in detail.
I made a few long distance QSOs with FT8 last year, and FT8 is sort of TDMA, in that it has some sensibility to latency in the software/hardware chain. I think the LimeRFE will do a lot to open the 1.2, 2.3 and 3.3 GHz bands to us SDR enthusiasts. Especially with the architecture being open. Good learning platforms.

Best,
Adrian