TX indicator PIN

Projects LimeSDR
#1

Hello,

I have a HMC349 chip and I would like to use it for switching beetwen TX and RX on one antenna.
Is it possible to controll it directly from LimeSDR, so whenever TX port is active it automatically selects it and when it finishes transmitting it goes back to RX?
I’m wondering if I could use any extra PIN to indicate that the transmition on one channel is taking place?

The other option I am considering is to switch HMC349, whenever there is already some voltage on the TX but I’m afraid it will be too slow and I will blow something up. I’m somewhat a beginner and can’t judge on my own if this idea makes any sense :slight_smile:

#2

On LimeSDR you can program 10 GPIO pins for various purposes. Simplest is to use one pin as TX/RX indicator, more complex is to use several pins as sequencer for RX/TX transitions (LNA, PA driver, PA final…). Another solution is VF VOX external circuit but it is much slower. Works great only for constant carrier based modulation like FM, for SSB or CW you need to add delay.

#3

Thank you for your answer! GPIO pins seem like a good place to start then.
Am I correct that I will need to mess with FPGA gateware to make this a constant change (not dependent on a client implementation - I would like it to behave in the same way, regardless of the application I’m using it with)? Or are there any shortcuts?

#4

LimeSDR API supports GPIO operations. No need to change FPGA, RX/TX transition time depends on used external switch IC and it is better to allow user app full control.