Tagged: PAL

Decoding the RF Output of a VCR with an RTL-SDR

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.

Decoding RF Output of a VCR with RTL-SDR Dongle

Decoding PAL Video from a Nintendo with An Airspy SDR Part 2

Oona combines composite output for color images.
Oona combines composite output for color images.

Last week we posted about Oona Räisänen's ([Windytan] and @windyoona) project to capture live video from her 1985 Nintendo Entertainment System (NES) using an Airspy SDR. In order to avoid expensive Video Capture cards which didn't work on her Mac, she used an Airspy SDR to decode the PAL composite video output of the NES. Last week she had black and white video working.

This week she has full color working, and has on her blog posted a write up about her project with the Airspy and her experiences with trying to find a suitable capture solution. She also goes into some detail about the CPU performance considerations of this solution, noting that there are some performance bottlenecks. She's also uploaded a video showing the results in action.

MacBook decodes PAL video via SDR

Decoding PAL Video from a Nintendo with an Airspy SDR

Oona (also known as [Windytan] and @windyoona) was recently looking for a way to capture PAL composite video from her old 1980’s Nintendo Entertainment System (NES) without spending a bunch of money on what are often poor video capture cards. As she already owned an Airspy SDR she decided to receive the PAL signal with the Airspy and modify some software to act as a PAL decoder.

PAL decoding was handled via some modifications to her private Tempest software. Normally Tempest type programs like TempestSDR that we covered in a [previous article] are used to spy on computer/TV monitors from signals that are unintentionally emitted in the surrounding area.

Oona has made the connection from the composite output directly to the SDR antenna input so it’s not unexpected that you’d have a strong signal. However, I have to admit that’s an incredibly clear image for a video being demodulated via a software radio.

What makes this an even more amazing feat is that the latency is low enough that it’s nearly playable using a computer and SDR in place of a television set.

We note that we’ve also seen SDRs used to decode standard PAL TV broadcasts before with an SDR# plugin called TVSharp.

Transmitting Analog TV Broadcasts with a HackRF

Over on the user submitted hackaday.io community, user marble has shared his work about using a HackRF to transmit PAL analog colored TV images with his rad1o (the rad1o is a slight variation of the HackRF One) using a GNU Radio flowgraph.

In his submission he shares a tutorial that explains the theory behind the PAL analog video standard. He explains the different components of the PAL signal, including the luma (black and white part), frame rates, and modulation. He then goes on to explain how color is encoded onto the PAL by using Quadrature Amplitude Modulation (QAM).

Finally in the files section marble also supplies us with the GNU Radio flowgraph which can be used to transmit PAL video with a HackRF.

PAL test signal transmitted with a HackRF.
PAL test signal transmitted with a HackRF.

New SDR# Plugin: PAL / SECAM TV

The SDR# plugins programmer over at rtl-sdr.ru has recently released a new plugin which allows the decoding of PAL / SECAM TV images from within SDR# (note link in Russian, use Google translate or see the download link at the bottom of the page). The author also writes that if you are using a newer software defined radio like an Airspy, you can also receive the audio channel using the SDR# multiple VFO plugin.

We note that there is also the TVSharp software by the same author which is a standalone program that can decode PAL and NTSC.

PAL / SECAM TV SDR# Plugin
PAL / SECAM TV SDR# Plugin

TVSharp Updated to Version 1.2

The PAL/NTSC analogue TV viewer TVSharp has recently been updated to version 1.2. This new version features an updated GUI as well as automatic frequency correction and automatic position correction. This may correct some of the scrolling and slanting problems seen in previous versions.

The latest TVSharp can be downloaded from here.

Word of warning: Chrome recognizes the download as malicious, however I have downloaded the file using FireFox and scanned it with Microsoft Security Essentials which found it to be clean.

TVSharp v1.2
TVSharp v1.2

Review of Various Lesser Known RTL-SDR Dongles

While the standard R820T dongles are the cheapest, most popular and best overall performing, there are other lesser known dongles variants out there which contain RTL2832 chips. Gough Lui has reviewed two lesser known dongles with Belling Lee (PAL) connectors on his blog.

One dongle uses the FC0013 tuner, and the other uses the R820T chip. Gough opens the dongles up and inspects their electronics and gives his opinions on the design.

One of the alternative R280T models with PAL antenna connectors
One of the alternative R280T models with a PAL antenna connector

Analogue TV with RTL-SDR

A user on the SDR# Google Groups forum has posted a program based on ADSB# called TVSharp, which can be used to watch analogue PAL and NTSC TV using the rtl-sdr dongle. Download TVSharp directly here (Mirror 1) (Old Version Mirror 2 (with source)).

The rtl-sdr as a software defined radio actually does not have enough bandwidth to receive a PAL or NTSC signal properly. PAL and NTSC signals require more than double the 2MHz typical bandwidth of the rtl-sdr. But, a decent black and white signal can still be obtained by using some of the luminance part of the signal.  As only part of the signal is sampled, resolution will be lost. Also, as sound is broadcast on a separate frequency, a second rtl-sdr dongle will be required to receive the matching audio.

On YouTube, users Superphish and ek6rc have posted videos showing TVSharp in action.

Analogue PAL TV with RTL SDR (RTL2832) and TVSharp

TVSharp R820T SDR sound via Yaesu VX-7:)