Before I get started on the post, I want to put a BIG THANK YOU out to @mariocannistra, @Zack and @IgnasJ for their help getting me aimed in the right direction for reprogramming my Lime-Mini. Especially @mariocannistra over the past week or so since we owned the same ‘Byte Blaster’ programmers for the Max10 FPGA on the Lime-Mini and Mario helped enormously with the troubleshooting of this with me - So a BIG SHOUT OUT to Mario, too…!
Okay - onto the transmit characterization for the Lime-Mini. Using SDRConsole V3.0 in transmit mode, I was able to characterize the transmit over the 30MHz to 1300 MHz region - - SDRConsole can only tune from 30 MHz and up right now, but is going to be operational in the lower HF bands later on. I will try to compile and use SDRAngel to collect that data over the next couple of days so there’s a complete picture here. I used LSB modulation and used a 1 kHz TUNE tone as the means to obtain the peak carrier over the whole range and it did fine. I also used a 1m length of RG 58A/U cable since that’s all I had on hand to couple the energy from the transmit port to the Agilent Spectrum Analyzer (E4401B). Pictures at the end of this post will show examples of the transmit spectra.
So with that covered, here are the measurements (MANY):
In a couple of instances I noticed that at 700 MHz and 1400 MHz SDRConsole wasn’t providing a TUNE signal and I have to think this is a purposeful software limitation (not an issue). Otherwise, the Lime-Mini performed STRONG over the whole band…!! I was really impressed that even up to 900 MHz it was still outputting nearly +10dBm. Clean spectra, too - no anomalies or issues in the spectra close to the carrier (within 1 MHz to 100 kHz).
Pictures follow, as does lower frequency HF performance when I have that running on SDRAngel - Stay tuned…!
Marty (and others),
Do you know why energy goes down as frequency increases? I guess it’s normal and not a bug, but I can’t see the explanation about it… Thank for anybody who will teach me some new thing
Sure do - The cable type I’m using is RG-58A/U cable (generally thought of as ‘garden variety’ cable). 1m of this cable has different attenuation values as frequency rises. As such, here is the attenuation of that 1m length of cable over the bandwidth I measured:
So, if you take the values I have recorded and extrapolate over the frequency range, you can ‘add back in’ the cable attenuation to get the real output of the Lime-Mini. I disregarded that because I knew coming into this that the cable would be a factor as the frequency got up to 1GHz and beyond - a more strict measurement system would have to be in place for those measurements to be taken and I don’t have that kind of lab equipment - most of my gear is good up to 1GHz and that’s it. A lot of other factors play into why the power appears to drop off and among those are: as noted - the cable attenuation, losses due to connectivity (BNC connectors instead of SMA), reactance differences between the Lime-Mini and the measurement system over the prescribed frequency range, coupling losses, etc. Any or all of those play into why the power level appears to drop above 1.2 GHz. But I know the Lime-Mini can transmit well above 2 GHz (and to 3.6 GHz if I’m not mistaken) but better measurement systems would have to be used to obtain that - again, I just don’t have that kind of gear to make those measurements up that high.
Overall I was generally impressed with the Lime-Mini’s power output over the range I tested it. It’s a wonderful little SDR for the price point and played real well with SDRConsole V3.0, too.
Hello @martywittrock
You’re very welcome, I’m always happy to contribute.
And thanks for your work and sharing these measurements.
Do you plan to measure also below 30 MHz ?
I know that less people are interested in that range but in the future I’d like to try and use the mini for VNA measurements of my HF solar,planetary antenna…
Yep - it’s my intention this evening to compile/build the SDRAngel app on Ubuntu 18.04 LTS and obtain the lower portion of the HF spectra that the Mini can operate to and also go back and fill the ‘holes’ at 700 MHz and 1.4 GHz in the data I took a couple of nights ago. I’m very curious as to how far down the HF Band the Mini will go so once I get 'Angel running and take the data I will post it without any delay - be looking for it over the next day or two…
I have gotten things to a point where I can complete the Lime Mini spectral power analysis at lower frequencies (lower than 10 MHz). I will work this through the week and let you know my findings - please do stay tuned…
Hello, @martywittrock I recently saw this post and was wondering how you got such a rather clean spectrum at 50MHz. It seems that my LimeSDR can not transmit a good enough sine wave below 500MHz. The spectrum is very poor. Do you know any way I can fix this?
I used SDRConsole for the testing, so I would advise that you use that app, too, for your tests. If it’s not producing a clean spectrum from SDRConsole, then I would suggest using the Lime Microsystems app for testing transmit because you can infinitely tune the filters in that app to suit the Lime Mini to be clean spectrally if SDRConsole isn’t producing what you need.
