Being a completely noob in SDR I have nevertheless embarked on writing my own transciever for the Mini using Gnu Radio Companion (GRC). Things work as expected above 30 MHz. TX output as per Marty’s measurements, even a couple of dB more and sensitivity OK.
But, below 30 MHz things go strange. I understand the idea (I hope) to use the NCO and do an up-converting. I use the formula: FNCO = 30 MHz - Foperate, and set the RX and TX frequencies to 30 MHz.
However, irrespectively of setting of the NCO frequency and RX/TX frequency, I can set the TX and/or RX frequency to any frequency, at least down to 3.5 MHz and the Mini tunes to the set frequency ,but RX sensitivity and TX power both decreases rapidly. At 24 MHz TX is down by 16 dB and RX sensitivity is down by 30 dB compared to 30 MHz and at 3.5 MHz TX is just above the specgtrum anlyzer’s noise floor.It seems to me the NCO setting in the GRC Lime source and sink do not work, but by some strange way the TX and RX synthesizers in the LMS7002 are simply tuned way below 30 MHz and their power decrease accounting for the decrease in power/sensitivity.
Please anybody who have tried tuning below 30 MHz using GRC with succes: What am I doing wrong?
P.s: You may wonder why I do not simply use SDR Console or SDRAngel. I could easily do that, but then I would not learn anything.