Friday, 26 December 2014

Playing with GPIB

Currently I am trying EZGPIB to do automated measurements, above is my
first attempt at measuring the output vs input in 1 dB steps of a 2m RF
brick RA06H1317M, the y axis is power in dBm. The yellow line is what it
should be and the blue line is what the amplifier actually produces.

Saturday, 20 December 2014

Initial 146.5 MHz DVB-S exciter tests

333KS/s 10 MHz BW
333KS/s 2 MHz BW
333KS/s 1 MHz BW

I thought I would share with you some initial tests of DATV-Express operating
at 146.5 Mhz. This is the exciter only, I will post some results of it combined
with a G.H Engineering brick based PA in a few days. These were taken with a
Rigol spectrum analyser. There was no additional filtering on the output.

The new FPGA code uses a x64 interpolater, it will only operate between about
100K and 400KS/s but this should be fine for the 2m DATV tests.

I was able to lock to the signal with an MER of around 28 using Tutioune with a
TT-Budget S2-1600 card. Work progresses on developing a matching
Software Receiver.  

Monday, 1 December 2014


Not having blogged for a while I thought I better do an update.
I have a number of projects on the go, one of the latest is using
NVIDIA's CUDA to do Software Defined Radio (SDR). I know
there is nothing too original about this but I wanted to learn how to
use CUDA and I thought SDR would be a place to start.

In the first picture you can see a waterfall of the 2 m band in a
Qt application,  it uses OpenGL and CUDA.
There is not much to see, just some APRS. I am currently working
on the software digital down converters. Using the various memory
resources on the NVIDIA card needs careful planning to obtain
maximum acceleration. I am expecting to be able to have at
least 10 receiver channels running on the card. I have some other ideas
for this Parallel computer like PAPR reduction in DVB-T2.

The SDR I am using is an Ettus research B200 which has a USB3
interface between itself and the P.C. The B200 operates from about
50 MHz to 6 GHz. With about a 32 MHz BW. I put mine in a
Hammond 1455L1601 box as it comes without a case.

The Graphics card I am using is a GTX 680 with 1536 CUDA cores. I am
planning to upgrade that to a GTX 690 which has twice as many cores.
The 690 is actually 2 GTX 680s on one card and appears as two
compute devices. Fortunately as these cards are aimed at the Gamer market
and high end Gamers like to have the best gear so the price of last generation
cards on the used markets is very reasonable. I found Gum Tree to be
a better place to buy them rather than eBay.

NVIDIA have just announced their Pascal chips with NVLINK which
will provide a quantum leap in performance. Those cards will be available
in 2016. They stack memory and CPU wafers on top of one another and
interconnect using Silicon vias. They will also allow much faster
communication with the host CPU through a shared memory interface.
Even with PCIe v 3 the global memory interface between the motherboard
and the GPU is the main bottle neck.

NVIDIA and partners like IBM are working hard to bring this technology
to other programming environments like Java and Python. They are also
providing application specific libraries for things like Deep Learning
Neural Networks. Maybe one day I will have a Neural Network to work
DX for me while I code.

Well that is it for now, back to my CUDA 6.5 programming / learning.

Wednesday, 10 September 2014

DATV-Express team win BATC Grant Dixon Award

I am pleased to announce that the DATV-Express team have won this year's BATC
Grant Dixon, G8CGK (SK) award for technical innovation.

Here are the links to the BATC talk

DATV-Express talk part 1
DATV-Express talk part 2

Sunday, 31 August 2014

August update

Not a lot to report, I finally managed to get the Verilog code to compile
into something other than a piece of wire, unfortunately the design was
too big to fit on the FPGA I am using so I am looking how to simplify it.

I have my talk for the BATC convention on the 6/7th of September
completed. It is a update of the current software situation and some
speculation of what might be in any possible DATV-Express 2.

We are always looking to fill a need in the hobby, if there is no need
then we won't need to develop anything.

I am giving a simpler talk and a demonstration to the Worthing Club on
the 17th of September.

There is an up and coming article in the next QST magazine  by Art WA8RMC
and Ken W6HHC is giving a talk at the TAPR DCC on the 6/7th of Sept.

There is a lot going on in the world of DATV at the moment and it is
difficult to track all the new developments.

I am hoping to do some networking at the BATC convention, find out what
others are doing and see where we can help, we don't want to duplicate what
others are doing.

If you attend any of my talks please say hello.

Tuesday, 29 July 2014

Winter projects stacking up

Diversity Receiver?
This is my winter project. I have been wanting to build a diversity SDR for quite
some time and finally I have the bits to make one.

To the left is a development board for an AD9253 quad 125 MS/sec 14 bit ADC.
The middle is an interposer board to adapt between the connectors used on the
ADC board and the FMC connector on the FPGA board. This board requires a
minor modification (to do with the framing clock signal). On the right is a Xilinx
SP601 evaluation board. The plan is to have a simple bit of code on the FPGA
to stitch together all the ICs, frame the data and send it over 1Gbit Ethernet to the
P.C for processing. The limiting factor is the 1Gbit Ethernet (of course).

Using Xilinx FPGA tools is new to me, (in the past I have used Altera) but I have
managed to write and deploy a simple program to the board. Xilinx have a different
way of doing things but the principals are the same.

Of course the FPGA board wants 5V and the AD9253 board 6V.

It will only be a 4 channel diversity receiver but that is a start but once I have verified
that it  works at HF I plan to add VHF / UHF / SHF down converters to it.

Sunday, 20 July 2014

Parallel Processing CUDA OpenGL UHD USRP2

For a bit of light relief the last few days I have been immersed in
CUDA and OpenGL programming. My initial goal is to use the
USRP2 I have to digitise a large piece of spectrum and display
it inside the window of a Qt5 application. I will be using CUDA to
do the parallel processing and OpenGL to display the results.

So far I have managed to create an OpenGL widget that displays a
window in a Qt application, grab samples using UHD, process
them using the CUDA library and write some simple kernel code.
I need to learn a bit more about using OpenGL before I go any further
as I want to display the results as a waterfall and getting CUDA to
talk to OpenGL via the GLWidget does not look too easy to do.
Getting CUDA to share buffers with OpenGL is not difficult but adding
the extra complexity of the GLWidget means I start to stray off the
beaten path.

The biggest problem has been installing the CUDA toolkit and more
especially the correct NVIDIA driver. The one that Ubuntu wants me
to install is not the right one. It has to be the latest one on the NVIDIA
website for CUDA 6.0 to work. I am using a GTX680 card for the GPUs.
I have also been looking at OpenCL but as I am using an NVIDIA card
I thought it better to use CUDA for the moment.

I bought the GTX680 a few years ago and for the same price I could get
something much more powerful now.

I notice it is not going to be long before Ubuntu 12.04 LTS is no longer
supported at which point I will have to consider upgrading. I have heard
upgrades never go smoothly so I am not looking forward to it.

I will post some more about Odroid in the next epistle.