50 MHz Tx performance, LimeSDR Mini 2.4

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

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

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

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

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.

Dave, did you ever solve the Low TX power? I am having teh smae problem and wanted to understand what you did that got the TX output power at 450MHz closer to the spec of 10dBm?

In LimeSuiteGUI ,

  • select Default;
  • In the TRF panel. set “TXFE output selection” to Band2;
  • In the SXT panel, enter the desired frequency and tap Calculate;
  • In the TRX Gain panel, tap on Alternative TRX gain source.
    With Frontend gain of 37, I see 2.5 dBm of output.

If you’re running limeGUI (Lime Suite NG), the same sequence. Note that the reset action is found in the menu item LMS7002.

However, I am yet to generate a signal using the LimeSuiteNG sink. I can see the device go through calibration but only an unsteady, small signal where I expect it.

Any advice on LimeSuiteNG sink would be appreciated.

Dave