Monday, 5 April 2010

More DVB

I spent far more time that I meant to on
DATV S/W development yesterday.
I have started to integrate some of the MPEG2
transport stream code into my DVB-S modulator.

One problem is keeping the modulator fed with the
correct number of bits. The original S/W I used
required calculation of the various stream bit rates
so that the correct number of null packets can be
added to pad it out to the wanted transmission bit rate.

To automate the process I have added the ability
for my code to monitor it's transmit queue length.
When the queue length falls below a certain threshold
it will now inject null transport packets into the
transmitted bit stream to pad the bit stream out to
the wanted transmit bit rate.

Gradually I will add more of the required packets
into the bit stream from my MPEG2 code and drop
the corresponding packet types from the original

I still have a problem though, the link between
the USRP2 and the P.C keeps dropping out for
a fraction of a second which causes the
transmission to momentarily break up.

What I am trying to do is well within the capabilities
of the USRP2 so I suspect I have not set my Linux
box up correctly to deal with the Ethernet interface.
Hopefully I can get this sorted out otherwise I am
going to have a very very major problem.

I know this Blog is getting a bit dull without any
pictures but most of the hardware I am using is
standard off the shelf stuff that can be found using
Google but I will try and put up some pictures later
in the week. I have not figured out how to take sexy
pictures of software yet (suggestions on a post card).


  1. To capture a picture of the program under windows you press SHIFT and the PRINT SCR key
    This copies a bitmap image to the clipboard, then you open a paint package and paste the image into the program edit as you want then save it out.
    I am not sure if this method works under linux, but it is worth a try
    HTH Mark

  2. Hi Mark, yes there is an equivalent for Linux. Can't remember what it is though.