Over on YouTube use Scelly has uploaded a video showing how he has used an RTL-SDR dongle and the TVSharp SDR# plugin to decode video from the RF output of an old VCR (videocassette recorder). VCR players were designed to output the same PAL or NTSC signal that old analog TV transmissions used, and the RF output of the VCR was connected directly to the TV's antenna input.
The TVSharp plugin for SDR# can be used to decode these signals, however as the bandwidth of PAL/NTSC signals is much larger than the 2.4 MHz provided by the RTL-SDR, only a black and white image can be received. Scelly writes:
RF Output from VCR connected directly to input of my RTL-SDR. The RF output is tuned to channel 22 (487.25 MHz), and as the signal is so wide, my RTL-SDR can only display the luminance data (black and white video) and audio, although not at the same time. If I had two RTL-SDRs or an SDR with a larger bandwidth, I could have both audio and video playing at the same time.
The video playing is "The Prince of Egypt" on VHS Video Cassette.
Over on his YouTube channel Aaron has uploaded a video showing how we can SigDigger to decode analog NTSC video from a drone camera which is transmitted at 5.7 GHz. SigDigger is a rapidly evolving SDR program for Linux and MacOS that has a lot of built in functionality for inspecting signals in more depth. Although not specifically designed for it, the Symbol Stream viewer in SigDigger can be used to display NTSC Analog Video. Aaron writes:
For the most part, the older an analog modulation is, the easier it is to get basic results when decoding. TV receivers were rather dumb back in the day, basically fast fax machines glued to an off-band FM radio receiver. Receiver circuits were also slow, and the signal had lots of invisible blank spaces in the borders so that the cheapest TVs could switch to the next line in time. The invention of Teletext leveraged those blanks in order to carry digital information and color information was embedded as an additional narrowband signal in the gaps in the spectrum.With this in mind I wanted to take a look at decoding analog video transmissions from drones. While some drones have moved to more effective digital compression and channel transmission technologies allowing for high definition video, there’s still drones using RC-like communications and the FPV video link is pure FM-modulated NTSC.
Searching the internet provided few results on how I could go about using low cost equipment, such as the HackRF One, to decode drone feeds. After an extensive search I decided to start looking at Linux based software defined radio applications I was already familiar with. By chance I happened to be working with SigDigger, a free digital signal analyzer. It has been discussed on RTL-SDR.com and more recently on Signal Lounge (https://signal-lounge.com/2020/05/05/sigdigger-for-signal-analysis/). It is also included in my own creation, DragonOS (https://sourceforge.net/projects/dragonos-lts/)
After a brief email exchange with the developer it was brought to my attention that visualizing analog video transmission is possible in SigDigger (although with no color information, of course). Since SigDigger supports the HackRF and the HackRF provides coverage in the 5ghz band, it was now possible for me to try to decode a 5ghz drone video feed. I’ve documented the process and my results on my YouTube channel. I should point out that this is currently a side feature of SigDigger and currently lacks synchronization. The symbol view area I used in the video is not made for this. It is meant to display symbols and symbols patterns which, due to its behavior, can incidentally show the contents of analog TV and weather faxes with lots of manual adjustments.
While the SigDigger developer makes mention of plans to include an embedded generic analog TV viewer and possibly add the ability to automatically sync video, there’s currently no timeframe on when that might become available.
DragonOS LTS SigDigger demodulating a 5 GHz analog video/FPV drone link (HackRF One, SigDigger)
We note that if you're interested in PAL/NTSC decoding, there is also the excellent TVSharp plugin for SDR# available.