50 MHz Tx performance, LimeSDR Mini 2.4

Projects LimeSDR
1

I am seeing low Tx output from my LimeSDR Mini 2.4 at 50 MHz. My intent is to use this device in a 6M transceiver.

The outputs measured with a spectrum analyser (good to only 500 MHz) are:

450 MHz, -8.7 dBm
350 MHz, -10.4 dBm
250 MHz, -16.8 dBm
150 MHz, -27.2 dBm
50 MHz, -46 dBm

The test software is LimeSuiteGUI (V23). Frequencies set manually in SXT. Gain set in TBB (Frontend gain). Input source set in TxTSP (Test signal, TSGFC -6 dB).

The fall in output hints at filtering in the Tx chain?

Does the test procedure look OK, please?

Am I missing some filter settings in LimeSuiteGUI, please?

Thanks

Dave

2

I’ve found
LimeSDR HF Performance - Myriad-RF Wiki

From the Tx curves in that report, it looks as if a LimeSDR Mini 2.4 performs like the LimeSDR TX1-2.

Is it sensible to think about mods to the Tx matching on the Mini 2.4 to get usable performance on HF, please? In my case, to drive my power amplifier I need 26 dBm of drive. 72 dB of gain in a driver amp would not be easy.

Dave

3

I apologize for not have been done more homework before posting.
Looking at the schematics, I see TX1-1 and TX1-2 are present. I also see Band1 and Band2 as options for TX RF port path in LimeSuiteGUI/Board Related Controls.
From the schematic, I expect Band 2 is the path for the lower frequencies.
However, choosing Band 2 gives even lower output:

  • Band 1 chosen: 450 MHz, -9 dBm; 50 MHz -46 dBm;
  • Band 2 chosen: 450 MHz, -46 dBm; 50 MHz, -67 dBm.

Does this narrow down the possibilities, please?

Dave

4

After digging into the doc (including an old performance assessment), my Mini generates the expected output on 50 MHz. With LimeSuiteGUI, Band 2 must be selected in the Board Related Controls panel, and as the TXFE setting in the TRF panel.

Dave

5

I checked with a colleague and he suggested that it sounded like the correct RFIC transmit port had been selected, but the RF switch on the SDR wasn’t set correctly.