DATV-Express Project - Febuary update report

[G4GUO]

Ken W6HHC has been unable to submit a report this month due to
the loss of his wife through bereavement. He has asked me to
include the following statement.

“Ken W6HHC dealt with the illness, death and burial of his wife in February.”

Things have been fairly quiet on the Express hardware side and most of what I
have been doing has been for the upgrade of my own DATV facilities.

A fair amount of time has been spent on investigating Digital Pre-distortion
(DPD). This has shown that useful improvements in the transmitted spectrum
can be gained through this technique. However it will require a new board
design to achieve the full potential of the method.

Some work has been done on making DATV-Express usable in a Windows environment.
I have written a small program that runs on a Windows P.C monitoring a UDP socket
and sending the received transport stream to the Express hardware for transmission.

I am using the signed drivers from the HPSDR project and the libusb library for
the USB interface with Express.

My current test set up uses vMix (a commercial Windows based video mixer from
a company in Australia) for video capture and mixing. This outputs the video and audio
as 2 directshow capture devices. I then use a directshow filtergraph to do the MPEG
encoding and transport stream multiplexing and UDP framing. The UDP transport stream
is then sent via the loopback address to the Express Server application which transmits
it over the air. It would also be possible to use FFMPEG in place of the filtergraph.
As you can imagine this opens up a huge number of possibilities.

The basic version of vMix is free, it supports 4 SD inputs, two of which can be capture
devices. The others can be captions or a virtual studio. If you want to do HD you will
have to pay for a licence but compared to other such programs they are not too expensive.

The quality of the transmitted signal will depend on how good the 3rd party codecs and
multiplexors are. For further details you can look at my blog
http://www.g4guo.blogspot.co.uk/

The last few days I have been working on a networked DATV box. This consists of a
DATV-Express board and an Odroid C1 board in a small Hammond box that sits on
my home Gigabit network. The Odroid C1 is a quadcore ARM board which costs the same
as a Raspberry PI 2. On the plus side it has better USB/Ethernet IO than the PI but
on the downside it has poorer software support.

To manage the box I am using a Web interface, I have an Apache webserver server running on
the Odroid which means I can control the system via any web browser. I am a total novice at
this sort of stuff though so progress is slow. My own goal is to have the studio located
in the nice warm house and the noisy transmitters located in the cold unheated brick
shed in the garden.

Yesterday for the first time I was able to transmit DATV from the shed, the webcam video
coming from my Windows 7 P.C in the house and the transmit receive switching being done
from an old iPhone 5 mobile phone. While it showed up some issues with the CGI script it did
work using 3 entirely different OSes with about 1 sec delay across the system.

The aim is not to produce an off the shelf set up for others but instead produce the building blocks
that will allow people to experiment and come up with their own novel solutions. There are
just so many different approaches open to us.

The Express team also supports the narrowband (<1 MHZ BW) DATV community and was represented
recently at a UK/France discussion on future paths for narrowband. The emphasis seems to be
moving from transmitters to better receiving equipment with a number of projects in the pipeline.

I continue to scan the Web for new and interesting technologies that can be used for DATV
in the future. There is always some interesting new silicon just around the corner!

I apologise for the rather egocentric tone of this report, hopefully normal service will
be resumed soon.

Kind regards to everyone from the DATV-Express team.

- Charles G4GUO