First tests of the LimeSDR with Gqrx

Broadcast FM reception with LimeSDR.

My LimeSDR board arrived on April 26, a day before the crowdfunding campaign was launched. I made an agreement to test the board and post my experiences here on the MyriadRF blog. This is the first out of hopefully many posts I will make about the LimeSDR.

Setting up the LimeSDR

I was a bit worried that the software support might not be quite ready for on-air testing. I wanted to test the LimeSDR using an existing SDR application like Gqrx. To that end, I was looking for driver library similar to librtlsdr or libairspy, which provides simple API to the hardware.

The LimeSDR uses the LMS7002M  programmable RF transceiver with digital interface. Consequently, it requires more setup than what we are used to from the simpler RF tuner chips.

Fortunately, my worries were unnecessary. Josh Blum has already added LimeSDR support to SoapySDR and the board could be accessed by Gqrx as a SoapySDR device. You can read more about this in the Lime Suite driver architecture blog post by Josh.

Thus, my task was limited to figuring out what sample rates and bandwidth settings I could use in Gqrx. I could use sample rates up to 10 Msps limited by my computer. More than enough for what I had in mind.

First signals

I guess the first on air test we always perform with a VHF SDR is reception of FM radio. FM radio stations are always there and strong, so they provide a useful “signal generator” when testing receivers. Needless to say, I was very happy when I saw the first pixels on the FFT plot and could hear the music from the radio station.

Receiving FM radio with LimeSDR and gqrx.

 

Amateur radio satellite reception

The next item on my agenda was to try receiving an amateur radio satellite. I connected a handheld Arrow II Yagi antenna directly to the receiver input of the LimeSDR, which is sufficient for receiving satellites in VHF and UHF.

All current amateur radio satellites are in low Earth orbit and have an altitude between 600 and 1000 km. Thus, the range to the satellite is usually few thousand km while it is in line of sight and the signals can become very weak.

The waterfall below shows my very first satellite reception done with the LimeSDR. The satellite was FO-29, which has a beacon sending Morse code and a linear transponder used as a “flying repeater”.

Satellite reception with LimeSDR and Gqrx.

The signals appear to drift in frequency because they are subject to Doppler shift. I have left the Doppler correction off to better illustrate that this is signal coming from an orbiting satellite.

A few days later I made another reception of FO-29. This time I observed a lot of extra carriers on the satellite downlink.

FO-29 downlink received with LimeSDR and gqrx.

These carriers have a different Doppler shift than the satellite beacon. Thus, they must be interference on the satellite uplink.

Weather satellite reception

After the FO-29 reception I have decided to also try receiving weather satellites.

The NOAA weather satellites are also in low Earth orbit. They continuously scan the Earth using various sensors and transmit the data down on VHF and L-band frequencies. The VHF transmissions are in the APT format, which is very easy to receive using the following workflow:

  1. Record WAV file with gqrx using the built-in APT FM mode.
  2. Convert the WAV file to 11025 Hz mono using sox.
  3. Process WAV file with wxtoimg.

And here are the first NOAA weather satellite images received with the LimeSDR. The first image shows the raw sensor data, which at the time of the reception was near infrared and thermal infrared.

Weather satellite image received with LimeSDR.

The next images is a false colour image generated by wxtoimg using HVC enhancement.

Weather satellite image received with LimeSDR.

You really don’t need a big setup for receiving satellites. NOAA APT transmissions are very strong and a simple Turnstile antenna is sufficient.

Turnstile antenna for satellite reception

The video below shows a reception in progress together with the simple antenna setup I was using. I recorded this video few days after I captured the image. Just to illustrate that receiving weather satellite images can be done with a simple setup.

What’s next?

There are two things I would really like to test before the crowdfunding campaign ends:

  1. Transmitting something
  2. Shortwave reception

Transmitting should not be a problem — all I need to do is create some GNU Radio programs.

On the other hand, tuning to shortwave frequencies requires some configuration on the LMS7002 that is not yet available to Gqrx, so that may take a little longer.

14 Responses to “First tests of the LimeSDR with Gqrx”

  1. Very nice and clean waterfall compare than my Hackrf i cant wait to get my LimeSDR in nov or dec in comparison looks like lime gonna be winner on all sdr platform.

  2. Anxious to get one of these to use as the basis for a multiband station for use in the Amateur Radio VHF contests: 50 MHz to 3.4 GHZ in one box! So need multi-receiver/transmitter software for 7 bands along with some band select output and PTT output……

  3. Thanks for the write up Alexandru.

    This SDR board would make an amazing multi-band amateur radio transceiver system for 144, 432, 1296, 2.4G and 3.4 G amateur bands.
    But it all comes down to the software to drive it.
    Need to RX & TX USB, CW, and FM.

    Although capable, I can’t see any need for a wide 60 MHz slice either, so computing power could be be significantly less.
    A 500 kHz chunk would be ample for most ham uses.

    Being able to run the software off a small single board computer (Pi etc) would be icing on the cake.

    73
    VK4GHZ

    • Adam,

      You are absolutely correct that it all comes down to the software. The good news is that many software developers, including myself, have already got a board and we have good time to develop end user applications until the boards are shipped at the end of the year.

  4. Hi, Alexandru – thanks for sharing your first impressions! They look quite impressive. I now am very curous about your first findings on HF. As I made some encouring results even with HackRF One with a 20 MHz bandwidth (with up-converter), LimeSDR should shine in also this respect. It’s all about to place the ca. 72 dB dynamic range (HackRF One: just 48 dB) carefully in a range which will combine highest sensitivity with lowest distortion. 73 Nils, DK8OK

    • I will do my best to get it up and running on HF but — given the limited time — I can not promise anything. I could of course test it with an upconverter, but it would be more interesting to test it’s native HF support.

  5. how does this compare to the SDR-Play which has HF and VHF filtering? i am looking at schematics and do not see such filters on this radio.

    • @MartinT, external filters are planned. If we’d have put filters for every band and application on the board, it would have been many times its current size and a great deal more expensive. Given we are not prejudging the application and LimeSDR is not targeting only amateur radio or cellular etc. it just wouldn’t have made sense to start putting lots of filters on there.

      I note also that SDR-Play is a single channel receiver only — whereas LimeSDR is 2×2 MIMO — covers up to 2GHz, instead of 3.8GHz, and with a fraction of the bandwidth. Plus LimeSDR also benefits from an FPGA which can be used for DSP offload.

      • Hi, Andrew
        Do you happen to know if there are any plans to include a facility to connect an external 10MHz reference – from, say, a GPS disciplined oscillator? I think this would be a useful addition to the board for applications at the upper end of the spectrum, and where the board is the IF for a higher bands transverter.

        73 de G8PEF
        John

  6. Hi, Alexandru
    I’d like to add my thanks to the growing chorus for your blog article.
    I also would dearly love to see transciever software for the VHF/UHF/Microwave amateur bands. I see the LimeSDR as the basis for a multi-band transciever for 50MHz–>3.4GHz bands, plus being the basis of transverters for the higher bands. Having the second channel would be great for operating the talkback links on 144 or 432 when operating on the higher bands.
    Fingers crossed for more developments on these fronts before delivery day 🙂

    73 de G8PEF
    John

  7. Hello Alexandru.
    Did you have the opportunity to test LimeSDR below 50 MHz ?
    I would be interested in using it for amateur radio astronomy in the 15-30 MHz range.
    Thank you and kind regards,
    Mario

  8. With that Altera chip on it it is far more similar to HPSDR and the Anan transceivers then it is to the HackRF or RTL-SDR gear.
    With that in mind the HPSDR crew have ported over a copy of PowerSDR to their hardware and it also runs a lot of other gear as well (you have to use their version though, the commercial version is FlexRadio only).
    It offloads a lot of processing onto the Altera chip and provides HF tx and rx in the ham bands.
    You might want to give that a go if you want to see what offloading to the Altera can do for it. I know when I get mine that is the first place I am headed for.

  9. Hi, what is the exact setup for Satellite data receiver? From cables, filters to antenna? I am an amateur and quite interested in SDR.

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