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.
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.
SDR-based PAL decoder is still black & white, but after a notch filter on the audio the picture quality is getting a lot better. pic.twitter.com/SUoBlnBZF3
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.
I’ve been looking for ways to capture NES video on my Mac. No easy+cheap solutions, but with some changes to my Tempest tool I can use the Airspy to receive the analog video carrier. The latency is almost good enough for playing, though it’s not my goal 🙂 pic.twitter.com/B6x44NEuvK
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.
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.
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.
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.
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 a PAL antenna connector
NOTE: Recent changes to WordPress seem to have broken the audio on this page. Please use the newSignal Identification Wikiwhich has many new signals. Anyone can edit and improve the information on the pages on the wiki.
A guide to help you identify some amateur and utility digital radio signals and sounds which you may find on the frequency spectrum. Most of these have been received with an RTL-SDR software defined radio. I will be slowly adding more to this list over time. If you enable stereo mix and pass the sample audio to an appropriate decoding program the sample audio should be decodable for most samples.
If you would like to suggest a modification or contribute a sample, please send a sample, waterfall image and information about the signal to [email protected], or post in the comments. (Note I am currently backlogged with contributed signals, if I haven’t replied or added your signal yet it will be done within a month or two).
Description:Terrestrial Trunked Radio (TETRA), also know as Trans-European Trunked Radio is a professional mobile radio and two-way transceiver (walkie-talkie) specification. Modulated with π/4 DQPSK. Audio sample recorded in NFM mode.
Common – 87.5 to 108.0 MHz OIRT – 65 to 74 MHz Japan – 76 to 90 MHz Consumer Wireless Devices – ~860 MHz
Mode: WFM
Bandwidth: 30000 Hz
Description: Stereo Wideband FM signal. Used for typical broadcast radio, and in some wireless headsets and speakers. This particular signal is from an AKG headset.
Top signal is WFM transmitted with low amplification. Bottom signal is WFM transmitted with high amplification.
Description: Single side band, specifically upper side band. Used in the HF band by amateur radio hams and aircraft weather reports. Single side band saves bandwidth.
Description: (Previously Unidentified Signal 5). Numbersstations are thought to transmit encoded information for various spy agencies around the world. They are recognized by a voice reading a sequence of numbers or words. This is a Cuban Numbers Station which has a data portion and a voice portion. Sound sample recorded in AM mode.
Thanks to Andrew from the comments section for the ID.
Description: (Previously Unidentified Signal 2). An Aircraft Communications Addressing and Reporting System (ACARS) data link that aircraft use to communicate short messages over long distances using HF signals.
Thanks to Andrew from the comments section for the ID.
Description: (Previously unidentified signal 10). Identified in the comments section by Ronen as an Asynchronous Frequency Shift Keying (AFSK) pager link. It is easier to transmit the FSK pager signal to the transmitter site as AFSK.
Description: Previously unidentified signal (11). Identified in the comments by various contributors as multiple overlapping RTTY signals sent by ham radios.
Voice Frequency Telegraph
Sample Audio:
Typical Frequency: 7453.50 KHz USB
Description: Previously unidentified signal (13). VFT or Voice Frequency Telegraph is one of several systems for sending multiple RTTY signals over one voice-bandwidth radio channel.
Portable Traffic Lights
Sample Audio:
Found Frequency: 154.463 MHz
Description: Previously unidentified signal (17). Identified by Peter via email as being signals sent from portable traffic lights that are often used at roadworks.
X2 on iDEN
Sample Audio: –
Found Frequency: 154.463 MHz
Description: iDEN is an acronym for Integrated Digital Enhanced Network and is a technology developed by Motorola. It is a type of trunked radio with cellular phone benefits.
If you know what any of these signals are please write in the comments. You can also submit any unidentified signals you would like to be added to [email protected]
(1)
Sample Audio:
Found Frequency: 171.3 MHz
Description: Recognized by DSD as a NXDN96 signal, but is disputed in the comments section. (Possibly a bug in DSD).
(3) – ALE?
Sample Audio:
Found Frequency: HF Band
Description: Sound sample recorded in USB mode. Potentially some sort of 2G ALE signal. Similar signal shown in balints HF tour video. Possible a weather map transmitted from Tokyo as noted in the comments section by Syd, or 4xFSK from China as identified by K2RCN in the comments.
(4)
Sample Audio:
Found Frequency: HF Band
Description: Periodic pulses. Sound sample recorded in USB mode. Possibly a GlobeWireless signal as identified in the comments section by K2RCN.
(6)
Sample Audio:
Found Frequency: 152.652 MHz
Description: Continuous signal. Audio sample recorded in NFM.
(7)
Sample Audio:
Found Frequency: 162.863 MHz
Description: Continuous bursts. Audio sample recorded in NFM.
(8)
Sample Audio:
Found Frequency: 457.168 MHz
Description: Audio sample recorded in NFM.
(10)
Sample Audio:
Found Frequency: 452.325 Mhz
Description: Sent in over email. Sounds like Motorola Type II smartnet, but Unitrunker does not recognize.
(12)
Sample Audio:
Found Frequency: 154.646 MHz
Description: Sent in over email. Repeats every minute.
(14)
Sample Audio:
Found Frequency: 433 MHz
Description: Sent in over email.
Hello! I was listening in the 433MHz band and saw this blip (about 1-2sec) on the waterfall on 433.873 (Millville, MA). It repeats about every 30-50 seconds, though doesn’t seem to be the same every time. Maybe a wireless instrument of some type (weather or something?). The only clear sound of it I could get was with AM, about a 4.2kHz wide filter (rtl-sdr, gqrx linux). Any ideas? Thanks!
(15)
Sample Audio:
Found Frequency: 455 MHz
Description: Sent in over email.
(16)
Sample Audio:
Found Frequency: 173.262 MHz
Description: Sent in over email.
(18)
Sample Audio: None
Found Frequency: ~856 MHz
Description: Sent in over email.
The antenna has a Yagi pointed to West from 23.5° South latitude, 47.46° West longitude. The signal can be local or from the sky. The signal is horizontal polarized.
(19)
Sample Audio:
Found Frequency: ~409.6 MHz
Description: Sent in over email. Recorded in NFM mode.
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
