Hello,
New to SDR and want to start with a standalone LTE Cell in B3 band.
I have seen a video With an intel NUC, Lime SDR, SRS-RAN software and duplex filter.
This is quite the same as I want to make
Since the RF output out of the Lime SDR is limited I need an PA to make the max 200mw output that is permitted in the NL (5mhz wide carrier)
How is the output from the Lime SDR, do I need extra filtering on the output of the PA?
I hope there is somebody who has done the same and can help me.
The cellular version of the LimeRFE would provide all the required filtering and driver and PA, plus LNA in the receive path and integrated duplexer. However, it seems that there is presently a long lead time on this.
As an alternative you could purchase a duplexer such as the sysmocom B3 one we have been using, then use driver and PA modules from e.g. Mini Circuits. Because of the high peak-to-average power ratio of the LTE waveform, bear in mind that you cannot drive an amplifier up to its rated CW output. A back-off of at least 6dB is typically required. It would also be wise to have a band pass filter between the LimeSDR Tx port and the amplifier chain, e.g. Mini Circuits VBF-1840+.
I’m afraid I cannot give you amplifier module part numbers at present, as we’ve not spent any time looking at this and done any testing, but it is on the to-do list. It’s going to take at least two suitably specified modules connected in series.
BTW, I’ve moved this post to the LibreCellular category so that it’s easier for others to find (and for me to reply further in future if I have more info to add).
Thank you very much for the information. I looked on the sysmocom website for the B3 dulplex, but I couldn’t locate it. I would be very grateful if you could specify this duplexer better so that I can locate it. At the moment, I am not using any duplexer, but using separated antennas for Tx and Rx. In Tx I’m using the Fairwaives PA module, SPA-030-27-01-SMA. This PA module has P1 dB: 30 dBm and 27 dB gain and operates in the range of 20 MHz to 3GHz. But, I’m keeping the maximum power on the PA output at 20dBm. With this output power, I am performing tests to verify if the spurious are within the 3GPP specification in the 700MHz, 850 MHz, 180 MHz and 2.6 MHz bands. Then I must carry out coverage tests with this power of 20dBm in a real rural environment. I am not using any PA in Rx. From your experience, do you think it will be necessary to use a PA on the RX? Best regards, Sindi
With its 30W power rating it is somewhat larger than needed for much lower power levels. However, it should provide good performance (isolation).
I think it would be typical to have an LNA in the receive path, but this of course depends upon the use case / environment and it would also be possible to make things worse by employing an LNA when the uplink signal is already strong (e.g. close range). sysmocom do also have a low cost 1800MHz LNA kit, but haven’t tried it out as yet.
Of course there are also suitable modules from Mini Circuits and others.
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