4 ms·

This is an awesome idea. I’ve questioned why the Amateur TV “channels” in the 430MHz range can’t be re-purposed for digital TV or just 6MHz wide pure data chann

by mikece 6y ago

This is an awesome idea. I’ve questioned why the Amateur TV “channels” in the 430MHz range can’t be re-purposed for digital TV or just 6MHz wide pure data channels (over which digital TV could be sent). Much of the resistance is from old HAMs who don’t want anything to change. Hopefully TAPR can get behind something like this as well as lobbying for updates to encryption where TLS over IP over amateur radio is happening.

drmpeg 6y ago
70 cm is a bit of a problem. 97.307(f)(6) limits data transmissions to 56 kbaud and 100 kHz bandwidth. However, digital TV is allowed. Some folks have circumvented the rule by sending a low bitrate video stream as a small part of their overall data. https://www.law.cornell.edu/cfr/text/47/97.307 https://www.law.cornell.edu/cfr/text/47/97.307
- aidenn0 6y ago
  What sort of effective bit-rate can you get at 56kbaud and 100kHz bandwidth with the allowed powers? If you can net 4 symbols after any error correction, that would yield the 100kbit TFA wants
  - drmpeg 6y ago
    DVB-S2 With 8PSK and 2/3 code rate would give 111 kbps at 56 kbaud. With 0.2 rolloff, the signal would be 67.2 kHz wide. The article is using FSK with a bandwidth of at least 300 kHz, so it's not legal in the US (for data only).
jlgaddis 6y ago
Some of us were doing ATV on the 70cm band 25 years ago.
dbcurtis 6y ago
DATV is a thing on 430. The problem is equipment. MDARC runs DVB-S, I believe. For DVB-S, you can re-purpose satellite equipment. KH6ATV is a proponent of DVB-T (which in theory should be better than DVB-S for terrestrial paths). There is one company in Taiwan that makes DVB-T transmitters and receivers that are usable in the ham bands (available in their E-Bay store), and people have done DVB-T in the ham bands with LimeSDR. BATC has done a lot of work with DVB also. Sorry to be vague, I haven't been keeping up on my reading... about 1.5 years ago I was going to try setting up for DVB-T on 430MHz and 1.2GHz, but life got in the way. In theory, you should be able to run 780p in a 6 MHz wide channel in the 430Hz band, or even squeeze 480i down to fit a 2MHz wide channel. (The max bandwidth allowed for amateur video in the USA on 430 is 6MHz, DVB-T does have 8MHz wide formats used in some countries for broadcast.) Contact KH6ATV if you are interested in doing some experiments. I recommend reading his notes first: https://kh6htv.com/application-notes/ https://kh6htv.com/application-notes/ For those that haven't stopped reading already: DVB-C -- optimized for cable. DVB-S -- optimized for satellite path loss and fading, but not for multi-path. DVB-T -- optimized for terrestrial paths which may suffer from significant multi-path propagation. ATSC -- The US standard, which unfortunately was standardized earlier than the rest and is expensive to generate and has outrageously poor weak-signal performance, both of which make it a ridiculously bad choice for amateur radio.
- drmpeg 6y ago
  ATSC can easily be generated with GNU Radio and any transmit capable SDR (such as the LimeSDR you mentioned). It's no worse than DVB-S as far as over the air performance. Many TV's will tune 70cm directly (cable channel 58 is 429 MHz). http://www.w6rz.net/imd78.png http://www.w6rz.net/imd78.png GNU Radio is also capable of transmitting DVB-S, DVB-S2, DVB-T, DVB-T2 and cable TV 64QAM/256QAM. With DVB-T2, you can even send a MIMO (actually MISO) signal with dual TX SDR's.
- aidenn0 6y ago
  My understanding is that ATSC has fine weak-signal performance at UHF in rural areas; it's just extremely sensitive to multipath interference and it doesn't do well with the terrestrial noise in the high VHF range, so anywhere with large flat surfaces (like city buildings) is not so great.

by mikece 6y ago

drmpeg 6y ago

70 cm is a bit of a problem. 97.307(f)(6) limits data transmissions to 56 kbaud and 100 kHz bandwidth. However, digital TV is allowed. Some folks have circumvented the rule by sending a low bitrate video stream as a small part of their overall data. https://www.law.cornell.edu/cfr/text/47/97.307 https://www.law.cornell.edu/cfr/text/47/97.307

aidenn0 6y ago
What sort of effective bit-rate can you get at 56kbaud and 100kHz bandwidth with the allowed powers? If you can net 4 symbols after any error correction, that would yield the 100kbit TFA wants
- drmpeg 6y ago
  DVB-S2 With 8PSK and 2/3 code rate would give 111 kbps at 56 kbaud. With 0.2 rolloff, the signal would be 67.2 kHz wide. The article is using FSK with a bandwidth of at least 300 kHz, so it's not legal in the US (for data only).

jlgaddis 6y ago

Some of us were doing ATV on the 70cm band 25 years ago.

dbcurtis 6y ago

DATV is a thing on 430. The problem is equipment. MDARC runs DVB-S, I believe. For DVB-S, you can re-purpose satellite equipment. KH6ATV is a proponent of DVB-T (which in theory should be better than DVB-S for terrestrial paths). There is one company in Taiwan that makes DVB-T transmitters and receivers that are usable in the ham bands (available in their E-Bay store), and people have done DVB-T in the ham bands with LimeSDR. BATC has done a lot of work with DVB also. Sorry to be vague, I haven't been keeping up on my reading... about 1.5 years ago I was going to try setting up for DVB-T on 430MHz and 1.2GHz, but life got in the way. In theory, you should be able to run 780p in a 6 MHz wide channel in the 430Hz band, or even squeeze 480i down to fit a 2MHz wide channel. (The max bandwidth allowed for amateur video in the USA on 430 is 6MHz, DVB-T does have 8MHz wide formats used in some countries for broadcast.) Contact KH6ATV if you are interested in doing some experiments. I recommend reading his notes first: https://kh6htv.com/application-notes/ https://kh6htv.com/application-notes/ For those that haven't stopped reading already: DVB-C -- optimized for cable. DVB-S -- optimized for satellite path loss and fading, but not for multi-path. DVB-T -- optimized for terrestrial paths which may suffer from significant multi-path propagation. ATSC -- The US standard, which unfortunately was standardized earlier than the rest and is expensive to generate and has outrageously poor weak-signal performance, both of which make it a ridiculously bad choice for amateur radio.

drmpeg 6y ago
ATSC can easily be generated with GNU Radio and any transmit capable SDR (such as the LimeSDR you mentioned). It's no worse than DVB-S as far as over the air performance. Many TV's will tune 70cm directly (cable channel 58 is 429 MHz). http://www.w6rz.net/imd78.png http://www.w6rz.net/imd78.png GNU Radio is also capable of transmitting DVB-S, DVB-S2, DVB-T, DVB-T2 and cable TV 64QAM/256QAM. With DVB-T2, you can even send a MIMO (actually MISO) signal with dual TX SDR's.
aidenn0 6y ago
My understanding is that ATSC has fine weak-signal performance at UHF in rural areas; it's just extremely sensitive to multipath interference and it doesn't do well with the terrestrial noise in the high VHF range, so anywhere with large flat surfaces (like city buildings) is not so great.