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.

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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

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HDSDR trackerball VFO project

I have been working on a trackball based controller for my HDSDR SDR project lately. This is a small R&D project that is run on my spare time where the goal is to determine if it is possible to use a trackball as a VFO for software defined radio (SDR) in contests. The project started out based on a demand for a more ergonomic way to operate a mult receiver in a contest environment that is less fatiguing during 48hours duration of a major contest like CQWW or CQWPX. The goal is that it should be possible to operate all radio functions you need from one hand only: VFO, speed of vfo, band, mode, filter width, volume, gain. I have modified a Marconi trackball and the controller is a Trinket Pro controller (Arduino)

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Single Sideband (SSB) modulation on the Raspberry PI

F5OEO has recently written some code to transmit a SSB signal using just the hardware in the Broadcom SOC chip on the Raspberry Pi.  You can find more info on this link http://www.rtl-sdr.com/transmitting-fm-am-ssb-sstv-and-fsq-with-just-a-raspberry-pi/

I tested the code on my RPI on 6m via a cable connection. It worked OK. If you look at the S-meter you can see that the envelope is constant. This is due to that the RPI has no way of modulating the envelope so the software actually modulates frequency. It is kind of constant envelope SSB.

Below you can see what the signal looks like. (This is received on a SDR via an attenuator). The signal is a bit too wide. However cool test.

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If you want to test the code yourself you can check it out over on F5OEO at github https://github.com/F5OEO/rpitx

Warning: do not connect the RPI GPIO output running this code to an external antenna without a bandpass or lowpass filter and a valid amateur radio license. Never transmit any signal outside the amateur bands.

Testing DxPatrol HF converter for Funcube dongle

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At Hamradio in Friedrichshafen I picked up a DxPatrol HF converter for the Funcube Dongle ( Supplier WiMo, designer: http://www.ct1ffu.com/site/ ). I was eager to test it on HF CW reception. To check the coarse frequency and operation of the local oscillator I used my Yaesu VX7R for detecting the signal from the board. (The DxPatrol HF converter can be given a voltage feed via the SMA from the Funcube Dongle, if you turn it on from your Funcube. Alternatively, you can feed it with power via the USB connector – only 5V and GND is connected internally of course. I wanted to check that the converter was operating by listening to the local osc with my VX7R).

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I was a bit surprised over the test result when listening to CW signals on HF. All the signals on the bands sounded like russian stations from the old days derifting all over the place. The local oscillator of the DxPatrol I purchased is unstable. It drifts so much that it can clearly be heard on CW. The designers of the DxPatrol unit told me to keep the unit free from wind when I asked about a possible design or osc issue via mail hehe 🙂 . I think a “slight mod” may be necessary … I have SI570 and a buffer in my mind….

SdrDx and Funcube dongle. Receiving airband traffic

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You should download and try out the new SdrDx console. It is compatible with your Funcube dongle. Finally a more advanced SDR console that has many of the features you need including several notch filters, memory functions, a very good and intuitive GUI. In fact I like the GUI style on this one! One minus is that it is not open source. The image above is a screen dump of Funcube receiver set to a QRG in the airband. The AM detector works very good. The SdrRx can be downloaded here at fyngyrz’s site  http://fyngyrz.com/?p=915

How to install SdrDx: Download zip. Unzip. Make a shortcut to the .exe file. If your Windows firewall gives you a warning, tell it to open up for that program. Make sure you have a new firmware installed on your Funcube (see other post for how to update).

HF converter for SDR Funcube dongle

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Tony CT1FFU and Diogo CT2IRW has released a converter for the Fun Cube dongle. The design is a based on the old NE602 workhorse. One new approach is to use a wideband MMIC amp in the front end. The unit is powered via a USB connector. Looks like this may be a good add on if you want to do some basic HF monitoring with the Fun Cube. You can find more information here: http://www.ct1ffu.com/site/index.php?option=com_content&view=article&id=178&Itemid=104

PowerSDR and Flex-Radio offerings becoming prime contest tools

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FlexRadio systems is launching new products and new improved software all the time. I have been following the SDR scene for several years now and experimenting with the Softrock 40 and softrock RX-TX as well as some earlier VHF SDRs has been fun.

I must say that the offerings from flex-radio is now becoming more tempting than many offerings from traditional suppliers like Yaesu and Icom. My FT-2000 with the latest software is surely a great radio (the best I have had so far) but I think a FLEX-5000A with diversity RX and the newest PowerSDR software must soon be tried in a serious contest effort. The filters, diversity functions and FFT bandscope functions are simply great. One thing that lacks are the feel of real buttons and controls. But that has also been taken care of (read below)

Here you can see a video from Flex-Radio where they take the new tracking notch filters (TNF-RF)  for a spin:

In case you lack the feeling of a real radio, DH1TW is here demonstrating the use of a DJ controller for adjusting VFO and other radio functions:

Surely great stuff! Stay tuned!