1 Sep
2017
1 Sep
'17
5:32 a.m.
Well aware of digital ATV, I'm the developer of the digital television
component of GNU Radio. The DVB-T2 DSP code was developed by myself and
Charles G4GUO. The DATVExpress transmitter board (that G4GUO is one of
the developers on) could be used for this project along with many other
transmit capable SDR's. However, the Ettus B2x0 is known to have the
best phase noise performance on microwave frequencies.
The cheap DVB-T dongles can work, but the latency of DVB-T is not
controllable due to a fixed "PHY" frame size. In DVB-T2, the frame size
can be made very small and this works wonders for latency. Currently,
I'm using a 3.458 millisecond frame size out of a maximum of 250
milliseconds. However, short frame sizes sacrifice throughput for latency.
The DVB-T2 receiver I'm using is not too expensive, only $69.
http://www.hauppauge.com/site/webstore2/webstore_pctv292e.html
The transmit functionality is accomplished by having an instance of Pcap
running in the GNU Radio ULE block. All the IP packets sent to the
normally receive only dvb0_0 interface are captured by Pcap before they
go to the bit bucket.
Ron W6RZ
On 09/01/2017 01:40 AM, Rob Janssen wrote:
Very interesting indeed!
You are probably aware that there is some activity on Digital ATV and
the boards made
for that purpose (and/or the cheap dongles they use) could be used for
this as well.
We have a Digital ATV repeater here that is currently under some
reconstruction, and I
have suggested putting some IP broadcast on the multiplex. Indeed, as
you note, a
Linux-based DVB receiver can easily put the demodulated and extracted
IP traffic on its
LAN interface. More than a decade ago I did some "experiment" logging
the downlink of
satellite-internet on a Dreambox and it just used standard features of
its software.
But your test of using this full-duplex (rather than just
unidirectional as it was envisioned)
surely is innovative.
It could be useful here as well, indeed as you indicate to make links
on amateur bands
for which there is no commercial WiFi equipment. It is not
straightforward to use that
equipment with transverters, and a steady fullduplex link would
certainly be easier.
Some people are also working on a 70cm digital access with smaller
bandwidth, there is
little detail on what modulation they use, it would be interesting to
see if using DVB-T2
in halfduplex more is feasible. Probably not, due to high turnaround
delays.
Rob
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