TXing WSPR with the Red Pitaya

Well,

You may recall some time ago that I had a fiddle with a Red Pitaya? This was back here in this post.

So further to the WSPR RX I was doing back then, I made a request via Mike Richards G4WNC (He writes the Data column in Practical Wireless) to add a PTT switch to the software. The TX signal was on the output connector and the RX input on the Input connector - I only have one antenna and I wanted to switch between the two.

Well, lo and indeed behold, the code for the Multiband WSPR transciever has been updated here.

I've downloaded the new software which includes an extra module called gpio-output which switches the DIO0_P pin (its pin 3 on the E1 connector) to 3.3V when the device is in TX.

Now, I noted a few things when I downloaded the new files and executed the make command:

1. The Makefile downloaded ended up with a .1 extension and needed to be renamed.
2. The new .sh files had the wrong permissions and needed to be chmod ed to be executable

other than that updating the software and re-building was easy. 
To accommodate this I have made a very simple PTT switch (please excuse my TinyCad capability):

which connects to the Red Pitaya Pin 3 and GND on the E1 connector and then feeds a PTT line (grounded during TX) to my TX/RX relay.

The only Relay I had was a latching type so I have made a board from W6PQL to drive the relay from a grounded line:

This board looked like this when I had it under test:

And this is what the latching signal looked like before I added some diodes on the relay coils:

Now, you may remember that I also purchased a board from SV1ASM to add some extra drive to the Red Pitaya output, here it is under test:

Now, this is supposed to give me about 14dB of gain, but my tests suggest it's a bit short. The Tracking Generator is at -20dB in the test below:

It may just be that I am not driving it hard enough in the test above, as I am getting more like 7dB gain. It seems to be good to about 100MHz though - I will look more at this later.

Before I hooked all this stuff up together, I did some tests on the Red Pitaya output lines. This 'scope screen grab is showing the TX output plus the IO line at 3v3 during TX:

And here we have the 'scope connections to the output connector and the E1 lines:

So, hooking all this lot together, we have a mess like this:

I need to make a low pass filter for the output; mine is currently configured to TX on 30M. Once I have the LP filter I will stick this on the air and see how far I can hear and be heard.

This project is now a good starting point for lots of other TX/RX type ideas on the board.... next though I think I am going to have a go at the Vector Network Analyser.

Here's Florrie the Ham cat being almost completely in the way throughout:

 Good egh?

SDR with the Red Pitaya

Well,

I came accross this board on the RS Components website, it's called a Red Pitaya:

Now this board is very much designed with RF and SDR (Software Defined Radio) in mind, it's got some very high speed ADCs (Analogue to Digital Converters) and DACs (Digital to Analogue Converters) on board - it also has a SoC (System On a Chip) with an ARM processor and a FPGA (field programmable gate array) pluis a whole other bunch of useful stuff also on-board.

Now, there's a very clever chap Pavel Demin who has written some fab and groovey software for the board to try a whole bunch of stuff from a simple SDR receiver all the way to a VNA (Vector Network Analyser). There has also been some interesting introductory articles to the board published in the Data Modes column in Practical Wireless.

I've been playing with the WSPR decoding software as a starter-for-10.

You have to go and get the software from the website here. You can download an image of the Red Pitaya boot device (memory card) and create the memory card for the device to boot from - I used Win32DiskImager for Windows - you could also use DD for Linux.

Once you have that device created you can boot the board from the card, then you need to access the board from your network - I used Advanced IP Scanner to find the board and then used Putty to create a SSH connection. From there it was a simple task of editiing the decode-wspr.sh file, adding my callsign and grid square and then rebooting.

I have the board configured (by editing the write-c2-files.cfg file) to decode 8 bands similtaneously (yes that's correct).

Here's a map of my decodes with the Windom connected to the input connector of the Red Pitaya (via a small attenuator pad for impedence matching).

I've also tried the SDR Receiver software with HDSDR configured to conenct to the RedPitaya SDR accross the network - it worked superbly.

I now intend to try to get the TX side of the SDR functioning - using WSPR first. To facilitate this we will need a bit more hardware. I found a great buffer amplifier design by SV1AFN here. I ordered the PCB only from him and here's the finished article (I am one SMA connector short of a party):

I'll also need a TX RX switch which I will create using a latching SMA relay I have here and a kit from W6PQL.

To move on to the VNA experiments I will need some other bits and bobs including this:

So, much more to follow!

Here' our Choppsy cat (AKA Git Basterd Cat from Hell):

Good, egh? Local conditions.