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Sunday, 17 July 2016

SDR with the Red Pitaya


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 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.

Saturday, 25 June 2016

New Amplifiermabob


I've been thinking for a while about upgrading the amplifiers I have here for 4/6M and also 2M. Here's the result of my investment:

The 950 deliveres 1KW on 6M (500W on 4M) and the 1000 is 1KW on 2M. Both solid state amplifiers from Beko in Germany.

Given the termoil on the currency markets as a result of Brexit - I might have just timed this right.

Local conditions.

Sunday, 19 June 2016

I've made another one!


You may recall the recent Frequency Reference that I made, I've just finished building another one for someone else! This one is almost identical except I have included a 1MHz low pass filter as this one will be configured to have a 1MHz fixed output.

Here's the 1MHz output:

Good, egh?

Friday, 3 June 2016

RTL on HF? no way!


I read with interest an article in Practical Wireless from June 2016 describing a neat looking receive converter to be placed up front of an RTL dongle type receiver.

These RTL devices are easy to find for a few GBP:

Here's the schematic of the converter:

And its built on a PCB from OHS Park which cost a staggering $5 USD for 3 including postage to the UK. They were delivered in a very timely manner too! 

You will see that I have actually built two - but basically we have a 50MHz oscillator and a mixer, so in the example below my SDR would be tuned to 70MHz and I would be listening to my signal generator on 20MHz. The output contains what you would expect from a mixer in that we have the input frequency, the on board oscillator frequency, their sum, their difference and all the other harmonics from this mixing process:

More to follow once I have it up and running with the RTL dongle, but so far so good!

Local conditions.

Monday, 30 May 2016

4M - Alive and well?


Some interesting propagation on 4M today. A beacon very loud from JN86:


Here's the 4M map from the great

Definately experiencing some "local conditions"

Good, egh?

Friday, 20 May 2016

Frequency Reference Completion


The project from last time is even in a box now:

Good egh?

You will see that we adhere to strict rules whereby the dogs are not allowed on the furnature:

Local conditions.

Tuesday, 17 May 2016

More Frequency Reference


Following my musings last time over the QRP Labs GPS module, I've now also built two further kits from QRP Labs. The S5351A Module and the VFO.

When you combine all these together in the way I have you can create a GPS disciplined frequency reference with two outputs.

One of the outputs can be fixed in the firmware and I plan to put mine on 10MHz, I've made a low pass filter for this output to clean out the harmonics. The other output can be user set to any frequency up to about 290MHz or so.

Here's the LPF for the 10MHz output:

And here's the 10MHz output before the LPF:

and after:

All good, egh?