DVB-T Dongle

[Robert Stratton]

Thanks for those insights! For people curious about Mobile DTV, there is a program for the PC from a company called decontis (I think. Their font makes it difficult to tell whether it's an i or a v.) that will pick the mobile data stream out and render it in some extremely version-specific instance of VLC. It works pretty well, and runs with all kinds of $14 and $20 receiver sticks. 

If you fire up TSreader you can also see what's there and which "channels" are encrypted, but I don't think Rod has built a parser for Mobile DTV yet. 

A while back I picked up an old but advanced-for-its-time LG portable DVD player that receives it. The screen's not great so the fact that the image has the pixel count of a postage stamp isn't particularly a problem. RCA (whoever that is these days) makes a relatively cheap mobile receiver that runs on 12V, if you want to pacify urchins. 

--Bob S.


----- Original Message -----
> 
> 
> Not Really. COFDM was much better around town where there is a lot of
> multipath. Out side of the city ATSC was better. The worse problem for both
> was distortion in the receiving end due to folks wanting to use amplifiers
> on their antennas.
> 
> 
> 
> I spoke with a number of people during the transition from NTSC to ATSC who
> lived across the river in Fairfax, Arlington and Alexandria who had bought a
> multi element antenna, then added a preamp and couldn't receive Ch. 48
> (Virtual Channel 4). When they bypassed the preamp things were better. They
> wanted to receive the Baltimore stations and that was the reason for the
> preamp.
> 
> 
> 
> We also got a large number of calls from out in Culpepper, Delaplaine and
> Paris, VA from people who used to receive Ch. 4. They were using outside
> antennas and I suspect what looked good (with fine grain noise) on Ch. 4
> (NTSC) became a victim of BER and the cliff effect on Ch. 48 (HDTV).
> 
> 
> 
> I used to check each complaint out using Terrain Analysis software to see
> what the path to their location looked like. In the majority of cases 30 to
> 35 miles out I don't think COFDM would have been of much use. It's hard to
> get UHF to penetrate a hill or mountain.
> 
> 
> 
> We did use COFDM for our news truck microwave back to the studio location and
> found QPSK with an FEC of 1/2 would get news stories in under almost all
> path conditions. When you went to higher bit rate FECs path conditions would
> start to take effect. When we started moving up to 32 and 64 QAM things
> became much trickier and your path had to have evev fewer obstacles (eg.
> Leaves on trees). Changing your FEC to increase data rates and decrease
> latency also had an effect.
> 
> 
> 
> I see Terry has also responded to your initial post and I will agree 100%
> with what he says. Yes there were many reasons behind ATSC becoming the
> system.
> 
> 
> 
> The comparison of ATSC and COFDM was done using a COMARK transmitter
> operating at 39 KW output power into an antenna (ERP was 894 KW) located
> 1020 feet above sea level in NW Washington, DC. We switched between the
> COFDM and ATSC exciters and maintained the same output power for both. MSTV
> had a truck containing measurement equipment out in the field and I believe
> the FCC was also out there making their own measurements. I still remember
> the folks from Sinclair down by the transmitter, with their battery powered
> COFDM TV receiver, making comments about how they could receive COFDM down
> there in the basement where the TX was located. Funny thing, I could also
> receive the ATSC on my receiver in the basement.
> 
> 
> 
> By the way, part of the ATSC data stream contains another service called
> mobile TV. It is basically .5 MB of data with 1 MB of error correction. It
> is intended for reception on small portable devices with small screens. It
> was not developed for home reception so HDTV receivers don't decode this in
> the data stream. The mobile stream works under severe multipath conditions,
> in fact, we received the ATSC signal that contained the mobile stream
> without any problem while going through the "E" street tunnel and all over
> down town DC amongst the tall buildings. We only lost lock briefly behind
> the Rayburn Building and in the 3rd Street Tunnel. Not bad for ATSC
> reception on a small receiver that was made by LG Electronics. Oh yes, the
> receiver also had a broken off antenna. Our route on this test was down
> Foxhall Road, onto the Whithurst Freeway, through the E Street Tunnel, then
> up to the Capital, back behind the Rayburn building, down to and thru the
> 3rd Stree tunnel, onto 14th street, across the 14th Street Bridge, over
> through Roslyn, up 29 to Glebe Rd., down Glebe and across Chain Bridge, up
> Arizona to Lougbroro returning Foxhall. Who says COFDM is the Cat's Meow?
> Not I said the Fly! And remember the modulation scheme is the ATSC method.
> 
> 
> 
> Bill
> 
> N4TS
> 
> 
> 
> -----Original Message-----
> From: Mike O'Dell [mailto:mo at ccr.org]
> Sent: Thursday, May 16, 2013 3:06 PM
> To: William Fenn
> Cc: tacos at amrad.org
> Subject: Re: FW: DVB-T Dongle
> 
> 
> 
> if I remember that test correctly, COFDM kicked VSB8's ass
> 
> from DC to Baltimore and back. Much less vulnerability
> 
> to multipath and more square miles per transmitted watt
> 
> in terms of coverage.
> 
> 
> 
> -mo
> 
> _______________________________________________
> Tacos mailing list
> Tacos at amrad.org
> https://amrad.org/mailman/listinfo/tacos
>