# USRP2 + WBX for DVB-T replaying **URL:** \ **Category:** GNU Radio\ **Created:** [May 3, 2013, 11:37pm UTC](https://www.ruby-forum.com/t/usrp2-wbx-for-dvb-t-replaying/228698 "2013-05-03T23:37:03Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Dinos\_Pastos](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/7c8e57/32.png) [@Dinos\_Pastos](https://www.ruby-forum.com/u/Dinos_Pastos)\ **Post date:** [May 3, 2013, 11:37pm UTC](https://www.ruby-forum.com/t/usrp2-wbx-for-dvb-t-replaying/228698/1 "2013-05-03T23:37:03Z")
Hi there, I have a USRP2 with WBX board which has been sitting around doing nothing. I was wondering if it is possible to use this hardware to get a live DVB-T signal and replay it back. What I want to do is to intercept entitlement management messages and modify/remove them on the fly. Please let me know if there is such support with this hardware or even a previous project that tackles this request. Regards Dino ---
**Author:** ![Dinos\_Pastos](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/7c8e57/32.png) [@Dinos\_Pastos](https://www.ruby-forum.com/u/Dinos_Pastos)\ **Post date:** [May 4, 2013, 4:32pm UTC](https://www.ruby-forum.com/t/usrp2-wbx-for-dvb-t-replaying/228698/2 "2013-05-04T16:32:44Z")
Hi Dino, DVB-T works in the UHF / VHF frequency bands, something you can tune your wbx at without problems. Bandwidth is about 8MHz (if I’m not mistaken), so that’s low enough. Since it sounds like you’ll be doing stuff offline (not in realtime), processing power is not a factor for your problem, either. DVB-T generally uses OFDM with large numbers of bins (2^11 or 2^13-bin fft), generous guard intervals and whatnot. A moderately complex system, but someone has already implemented a dvb-t modulator in GNU Radio[1], you can take a look at that, but I doubt it would work with current versions of GNU Radio. Regarding to your EMM “hint”: You do have to realize that EMMs are rather “high level” concepts; you need to encode them into a data stream, mux them together with the video stream, encode that whole thing, map it to the correct OFDM carriers and transmit that. Since what we’re talking about are messages meant to inform decryption devices about their working state, I guess it won’t be as easy as replaying EMMs you captured, since it most probably carries keys for specific content. Then, on the other hand, TV encryption in the 90s has gained notority for being broken shortly after deployment, so this is actually an interesting field of research for someone with a cryptographic background (which I can’t claim to have). Happy hacking Marcus [1] PELLEGRINI, Vincenzo; BACCI, Giacomo; LUISE, Marco. Soft-dvb: A fully-software gnuradio-based etsi dvb-t modulator. Proc. WSR, 2008, 8. Jg. Am 03.05.2013 23:35, schrieb Dinos Pastos: ---
**Author:** ![Dinos\_Pastos](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/7c8e57/32.png) [@Dinos\_Pastos](https://www.ruby-forum.com/u/Dinos_Pastos)\ **Post date:** [May 5, 2013, 9:02am UTC](https://www.ruby-forum.com/t/usrp2-wbx-for-dvb-t-replaying/228698/3 "2013-05-05T09:02:24Z")
Thanks for the info I do need it to be real time actually As for your concerns about the Emm. All I need to do is disable one not edit it, so it’s either a re package of the steam or a jam of a specific header. Can you point me to a working dvb-t project? Thanks again ---
**Author:** ![Dinos\_Pastos](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/7c8e57/32.png) [@Dinos\_Pastos](https://www.ruby-forum.com/u/Dinos_Pastos)\ **Post date:** [May 6, 2013, 4:34pm UTC](https://www.ruby-forum.com/t/usrp2-wbx-for-dvb-t-replaying/228698/4 "2013-05-06T16:34:41Z")
> Thanks for the info > I do need it to be real time actually > Doable. > As for your concerns about the Emm. All I need to do is disable one not > edit it, so it’s either a re package of the steam or a jam of a specific > header. > I understand that, but I guess you don’t understand the way the multiple > streams of data get combined in dvb-t: It’s not like you tune your > receiver to the “video channel”, the “audio channel” and the “additional > data channel”; these data streams are heavily interleaved. > You do have to deinterleave them to modify/jam only specific parts. > Then, of course, you’ll need the knowledge of how an EMM actually looks > like to intercept it; and then you need to interleave it to get a > working dvb-t transmission. > It’s not like “I choose to jam frequency range x-y, therefore my card > never notices that it shouldn’t decode PayTV”, it needs a understanding > of the way DVB-T transports different kinds of information, from the > highlevel point of view of “video, audio and EMMs” down to the physical > layer of QAM on 8096-OFDM. I hope that helps defining the situation better. > Can you point me to a working dvb-t project? > Uhh.. actually I’d start googling as much as you would. Hope that helped, Greetings, Marcus