Notice there is a spike on the left edge - this is the “pilot tone”, at precisely. For example, RF channel 36 is 602–608 MHz, centered at 605 MHz.Ĭonfigure an 8 MHz bandwidth (enough to cover the 6 MHz of ATSC, and then some) in GQRX, and tune to the center frequency, 605 MHz in my case, and a strong ATSC signal should be visible:Ħ MHz ATSC signal. Wikipedia gives a lower edge and upper edge, add +3 MHz to the lower edge to get the center. Find a strong ATSC signal in your area, find the RF channel, then lookup the frequency ranges from North American television frequencies. To capture the signal from the air to disk, try gqrx. The raw IQ captures grow large quickly, so having a fast RAM disk for saving and loading can mean the difference between overloading and not. Hdiutil attach -nomount ram://4000000 diskutil eraseVolume HFS+ ramdisk /dev/disk4 To read/write data quickly, create a RAM disk: Open this file in gnuradio-companion, the flowgraph is straightforward:Įditing file_atsc_rx to read Complex files instead of ShortsĬomplex floating-point is the native format saved by GQRX, so if the flowgraph is adjusted to read in this format no conversion is needed. Gnuradio/gr-dtv/examples/file_atsc_rx.grc First find the GNU Radio ATSC receive example file: I found that article quite helpful, even without an SDRplay and Windows. Introducing GNU Radio’s file_atsc_rxīack to the Watching ATSC HDTV on the SDRplay RSP tutorial. Some stations transmit up to a dozen or so subchannels. Digital television is efficient enough to allow multiple simultaneous video/audio/data streams, so the subchannel identifies the specific stream in the broadcast. What is this minor number? The “subchannel”, another 10-bit number chosen by the broadcaster. The FCC website uses dashes so I’ll use that as well. These may be separated by a dot, but that can be misleading since it is not a decimal number (unlike, say, FM frequencies, which are decimal numbers), or a dash, although that can be misleading too since it is not a range. The virtual channel has two parts, a major and minor number. The virtual channel is listed first, but you can click the callsign to see the RF channel.Ī virtual channel number, including the subchannel.īut that’s not all. The FCC helpfully provides a website of DTV Reception Maps, where you can enter your address and see what channels you can expect to receive. By contrast, the RF channel is always determined by the frequency (554–560 is still “RF channel 28”). This is known as the “virtual channel number”.
Any 10-bit number can be transmitted (0–1023), arbitrarily. The “channel number” for 554–560 MHz, if there is one, is chosen by the broadcaster, embedded within the transmission stream. With ATSC, this relationship is not so straightforward.
#Hackrf one ham it up tv#
In the old days of NTSC analog television, largely phased out since 2009, the channel you see on your TV set would always map to a fixed frequency, e.g. In this post I’ll use the HackRF One (20 MHz bandwidth, plenty enough to cover ATSC, and then some) since that’s what I have readily available, but others have had success with the SDRplay, see: Watching ATSC HDTV on the SDRplay RSP Virtual channels & subchannelsīefore we begin to tune into the radio spectrum we need to know how the television “channels” correspond to frequencies.
However, there are several mid-range SDR transceivers available with greater bandwidth encompassing ATSC. You could solder multiple RTL-SDRs together and use something like multi-rtl, in an attempt to attain the 6 MHz bandwidth required for receiving digital television signals. This SDR mode only supports a bandwidth of 3 MHz, at best, not nearly enough for receiving DVB-T, nor ATSC (6 MHz) for that matter. RTL2832 has a hardware demodulator for DVT-B (a 5 MHz - 7 MHz signal), in addition to the software-based mode, where the analog-to-digital converter passes raw IQ samples to the host computer for processing. Well it turns out, despite the common use case of these RTL2832U-based DVB-T receivers as SDRs, they don’t perform television signal demodulation in software. Waterfall graph of ATSC channel 36 (602 MHz - 608 MHz)