Wednesday, 26 March 2014

Sockit Zipper and Myriad

This is a project for later in the year. What you are seeing is an Altera Sockit kit.
The main chip combines a Cyclone V FPGA and dual core ARM processors on
one piece of silicon. The board has both a Gigabit Ethernet and a VGA output
as well as sound i/o and a number of USB2 connectors. As you can see this
screams "I want to be an SDR".

To the right is a Myriad RF board and its associated Zipper interface adapter.
The chip on the Myriad board a LMS6002D currently operates from
300 MHz to 3.8 GHz. Lime have announced a new chip LMS7002M which
will have an extended frequency range 50 MHz to 3.8 GHz and boasts
2 complete transceivers. 

The Zipper board allows Myriad to be used on either Xilinx FPGA boards
that have an FMC connector or on Altera boards that have HSMC connectors.
It also adds a USB to I2S chip to program the Lime microsystems chip and a
programmable clock generator.

There are already a  number of Linux ports to run on the Sockit board. I have
also spoken to one of the clever people at TAPR and he suggested that I might
like to use the work done on HPSDR which should be easy to move to this
board. He is planning to do something similar himself.

This will give me a chance to learn to use the Avalon fabric promoted by Altera.
Avalon is licence free and forms a way of connecting FPGA blocks together in
a relatively painless manor using their QSys tool.

Technology just gets better and better.

Monday, 24 March 2014

DVB-S running on the FPGA

Just a note to let you know that after many weeks of work I have finally
managed to get the DVB-S encoding moved into the FPGA. This offloads
about 60% of the processing from the host to the FPGA and will allow
me to use a Raspberry PI with Express.

I am hoping to have a demonstration transceiver based on the PI and Express
ready in time for CAT14 in September. The system will use MPEG4 video.
The video will be captured with the PI's webcam and the audio with a
Wolfson sound board. For receive I plan to use a USB DVB-S dongle.

In the process I will also provide a module to allow Express to be used
with the MK808 standalone system pioneered by Rob M0DTS.

I was going to post something about MyriadRF but I had a problem with
the batteries in my camera so that will have to wait until another day. 

Friday, 14 February 2014

Crazyscan2 and TBS 6280

I finally managed to track down a TBS 6280 PCI card that I could use for testing
DATV-Express. A TBS 6220 card would have worked just as well. So above is
a constellation display of DATV-Express transmitting 64QAM with 7 MHz
channel spacing and 2k FFT. It seems that while it does work just with the FPGA
producing the clock it works a lot better with an Si570 fitted. The program I am
using to do the display is crazyscan2.

Wednesday, 5 February 2014

Boxed and booted

Boxed DATV-Express with tri-band stubby

As you will know by now, DATV-Express boards are on sale to Radio Amateurs.
Our first batch of boards has almost sold out, hopefully the feedback we get from
the first of the few will enable us to improve what we have to offer. 

The next item on the list is a variant of the software that will work with small
embedded systems. To shed some of the CPU load we will be working to move
the DVB-S encoding from the host computer onto the FPGA on the board itself.

This has been a steep learning curve for myself and the others on the team. I am not
sure I would want to do another project like this but if I ever do, what I have learn't
on this project will make the next one much easier.

The software will develop over the next few years so watch this space as they say.

Wednesday, 29 January 2014

Trouble with aliases

2k mode using 2048 iFFT
2k mode using 4096 iFFT

The top picture is 2k mode DVB-T being generated with a 2048 point iFFT
notice the aliases either side. The lower picture is the same DVB-T mode
but this time being generated using a 4096 point iFFT only the centre bins
were used, the others filled with zeros. Of course to get the same bandwidth
(in this case 2 MHz) the second iFFT has to be clocked out at twice the
frequency.  The difference in the far out noise is down to me not setting the
levels the same in both traces, but I wanted to show you the aliases.
I learn a new DSP trick every day!

Side-band Suppression
This picture shows the DATV-Express board being modulated with a minus 1MHz
tone. The peak at the left is the LSB, the one in the middle is the un suppressed carrier
at 437 MHz and the one just above that is the unsuppressed USB. The one to the far
right is a harmonic of the modulating tone.

Wednesday, 22 January 2014

DATV-Express Jan latest

7 MHz DVB-T tx DATV-Express rx RTL Dongle and DVB Dream

Some progress has been made on the DATV-Express software.
The latest build is more stable although some problems with
the PCR still remain.

I have done some testing of the DVB-T software on 6/7/8 MHz
channels and that appears all to be working now. When I moved
from a fixed point iFFT to a floating point iFFT I neglected to
change the pilot tone lookup table from short to float and that
was why it stopped working. Rob M0DTS has also done some
testing and has been able to receive the low powered DVB-T
signal on his domestic TV.

The software also supports 2/3/4 MHz channels. I am hoping to
test that soon as I have just purchased a UT100D demodulator
from the Hides eBay store. As the 2/3/4 modes are simply scaled
down versions of the 6/7/8 channel modes I am expecting it to work.

My preferred solution for receiving DATV on a Windows P.C is
the excellent DVB Dream software, it is not free but has a manual
scan screen that allows you to set the parameters yourself.

The observant of you may have noticed there is a blank space on the
PCB for a Si570 clock generator. I have now added support for that
chip in the main code. The chip is quite expensive and not needed
for DVB-S, it now looks like it is not needed for DVB-T either as the
clock generator in the FPGA seems to do as good a job.

Monday, 30 December 2013

DATV-Express launch delayed

We are still having software issues with DATV-Express.
Rather than release an unreliable product we have decided
to delay the launch. There are two main issues, firstly the board
does not always configure itself correctly, this can cause it to
generate either an off frequency or distorted signal and secondly
there are issues with providing an accurate PCR, this can cause
lock ups of the picture. We do not expect a launch before June 2014.

Update: The board configuration issue now seems to have been fixed.