New front end for use of the Red Pitaya in SDR applications

The Red Pitaya SDR board is based on the Xilinx Zync SOC and has 14 bit external A/D converters. However, for SDR usage on the HF bands from 0.1-30 MHz (and for that matter up to 50 MHz) the Red Pitaya is a bit “deaf” in the stock configuration. I have made a broadband amplifier that has a fairly high gain and very good IIP3 properties. Below I have posed some pictures of the prototype amplifier.

20160424_153046-1This is the prototype amplifier. I inserted a ferrite ring on the input lead to roll off the VHF / UHF sensitivity to reduce problems with nearby broadcasters etc. There is a also a PI network attenuator on the ouput and I have inserted a couple of beads in that as well to roll of the outpu response when frequency increases. The other components in the lower part is a input pi attenuator I used when I did some VNA frequency response measurements. This as well as the RCA plus is not used (RCA plugs are surprisingly good for low level RF signal routing in the HF bands and nice to use in the lab).  I used a more professional attenuator with a large attenuation range and flat response to determine the proper attenuation level after the preamp into the Red Pitaya. Reducing gain after the first amplifier has very little effect on the noise figure. Reducing it before the first amplifier directly adds to the noise figure. I added some protection diodes over the input to reduce the risk of strong RF signals or static voltage build up damaging the input. Below I am measuring the response of the attenuator with the DG8SAQ VNA. It was flat from 0-1,3 GHz.

20160424_203234-1

20160424_14035020160424_232930

 

 

 

Red Pitaya SDR TX / RX

The Red Pitaya hardware is the first low cost RX / TX capable SDR hw to come onto the market that is open source and can match the Ettus Research USRP periperhal. It has a combined CPU and FPGA signal chain with  two channels 14 bit 125 MSPS A/D and D/A. It also has a Dual core ARM Cortex A9+ FPGA (Xilinx Zynq 7010 system on chip). Only a few years ago this caliber of hardware had to be custom designed and was typically used in radar antijamming systems, radar signature classification systems, ultrasound, sonar and in high end vibration analysis tools (as examples). The ARM CPU on board can run Linux and it has GNU-Radio support. For fast data transfer there is a GBE (Gibabit Ethernet) interface to other host systems. With a a RTOS on the ARM core or a zero copy IP stack under Linux it should be possible to approach fairly close to 1 Gbit/sek transfer rates to host systems (if needed).
References:
http://www.rs-online.com/designspark/electronics/eng/nodes/view/type:design-centre/slug:red-pitaya
http://wiki.redpitaya.com/index.php?title=Hardware_Overview

20160408_14423420160408_144812

533c13a78bf449debc9d183e0ab30198600px-RedPitaya_HW_architecture