Re: LimeSDR Mini - Es 'hail2 - TX at 2.4 GHz

Clive Sanders

Firstly my thanks to Simon for the ongoing work and also to add to Roberts comment.  Whilst having no problem getting the Lime mini to transmit I do agree with the observation regarding its initialisation routine leaving it in transmit.  Once the PTT button is operated it works normally so it would appear that something in the start-up routine is responsible. I don't think it's really safe to put it onto a 'live' system whilst this occurs.

As a matter of interest I have over the last few days done some tests on the Lime mini involving injecting an external clock.  I think the support for this in SDR console's settings are a left over from the Lime USB.  The external clock in the mini is actually applied by physically switching R59/62 an  i.e. a hardware modification has to be applied and the switch from internal clock to external cannot be made by software alone.

Doing some tests with Lime Suite the mini seems a bit 'picky' regarding the external clock values it runs with and I ended up using 40MHZ which is the same as the internal VCTCXO,  having done that another problem manifest itself as the mini then fails the stock quick tests and calibrations (I noticed also that the SDR console log threw errors as well).  The errors relate to the fact that the mini's VCTCXO is, it would seem, 'exercised' by the DAC providing it's control voltage and expects to see a corresponding change in the VCTCXO's output frequency a reasonable test to be applied to ensure overall functionality but clearly with the internal oscillator disconnected cannot take place.

I ended up restoring the original hardware link to the internal VCTCXO and trimmed its 40MHZ output by means of a loosely coupled and GPS locked service monitor whilst adjusting the DAC via Lime Suite. The final value is then written to the mini and persists.  I would though say that a degree of luck is needed to hit the right frequency as the DAC resolution is quite coarse. This I see is already documented in the Myriad Discourse forum where a possible substitution of the DAC is suggested it would though require also that the software is rehashed accordingly.

I'm a newcomer to the Lime mini and find it a great little device to play with and it works well as a receiver with SDR Console.  My initial tests on transmit have on occasion caused SDR Console to crash but when it works it is good.  I have just made up a small amplifier with 2.4 GHz SAW filtering and Gali-84+ to move towards a rx/tx solution to use with my existing 2.4GHz PA once the initialisation issues are resolved.


Clive, G4KCM

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