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@ -8,4 +8,136 @@ Experiments in audio-visual transmissions (tags: narrowcasting, microfm, microtv
## Prior Art
Based on Tetsuo Kogawa's simplest tv transmitter
* You sharing a room with a analog CRT Television set in Europe (NL) (empty analog tv bands)
* <del> You have a HAM radio license and call sign (legally usable section of the band (6meter, 50MHz)) > TV signal's bandwidth is too high to be legally transmitted (4.5MHz). Only sstv is allowed on carrier: 50.510 MHz, with Bandwidth of: 1.2000Mhz (Our signal is 4.5Mhz....)</del>
This is illegal. Don't make it. What can you transmit with license:
* 4 ingredients: Frequency, Bandwidth, Transmit Power, Mode
* Novice callsign:
* "Beperkte machtiging alleen voor de 40-m-, 20-m-, 10-m-, 2-m- en 70-cm-band met een maximum zendvermogen van 25 Watt. (
* 144.500 - 144.800 MHz > all modes, 25 Watt, ...but yes..800KHz bandwidth, our signal is 4.5MHz (2 meter band)
* 434.000 - 435.000 MHz > experiments, atv, 25 Watt, 1Mhz bandwidth...image: AM modulated, soundFM modulated ( (70 cm band)
Instead of saying 144.500 MHz, these amateur bands are often refered to in meters rather than frequencies. These are the literal wavelenghts of the signal. The 'meter' bands are calculated by speed of light in a vacuum 300 million meters per second divided by frequency in million Hertz/sec (so 300/50Mhz=6 = 'the 6 meter band' )
[TV] ....(air)..... [TRANSMITTER]---(RCA CABLE)---[RPI]---(INTERNET*)
### Hardware
Raspberry Pi 1 B (fcc id: 2ABCB-RPI21), the first raspbberry pi board (2011-2012), for fullsizecomposite out (RCA) plug.
OR: RPI 3b v2 has composite out trough the minijack trrs connector. NOTE: the ground and + are inverted on this plug... (so centerpin on yellow plug is ground and sleeve is your signal). This also destroys the sound output on the trrs...great job rpi!
### Winding coils and soldering
Use a 5mm drill bit to wind your coil around. (coil = 7 tight turns of 0.7mm (measured 0.6mm) around a 5mm drill bit, after winding TIGHT, spread the coil out to be around 7mm/7.5mm in lenght, coild-end to coil end...).
### Parts
* Transitor - Kogawas japanese transitors are from the 1970's and unobtainable, but you can use practically any general purpose NPN transistor: BC547b, BC548b, 2N3904 just take notice of the pins and orientation.
* 2x Variable Capacitors - Instead of 10PF, we used the 50PF Murata TZ03Z500F169B00 Trimmer Cap
* 2x Ceramic capacitor 0.01uF / 10nF / 103
* 1x Electrolytic capacitor 100uF
* 1x 1k / 1000R / 102 Trimmer Potentiometer
* 1x 10K Ohm THT resistor:
* 1x 27K Ohm THT resistor:
* DIY: 1x Coil: 7 turns, 0.7mm magnet wire/transformer wire (width 6.8mm)
* 9 Volt Battery
* 9 Volt Battery Clip:
Complete Bill of Material:
10 parts, total costs: $1.49
### Tools
* Side Cutters
* 5mm drill
* Soldering Iron
* Solder
* Small set of screwdrivers for tuning (plastic prefered)
* Utility knife
* Super Glue
* Vernier Calipers
## Tuning the transmitter
roughly 6 variables:
* Input Voltage
* Antenna (Type+ Size)
* Coil (Material, diameter, length, wire gauge)
* Variable Capatitor 1 and 2
* Variable Resistor
* You position to the transmitter(+ transmitter is microphonic like a contact mic)
Preferably you use plastic screwdrivers to adjust the variable caps and resistors..this is not always possible, maybe coating your screwdriver in non conductive paint could work.
The exact transmitting frequency will always be a surprise. Usingt a SDR like HackRF + software like GQRX helps to find your transmitter's frequency in its 'waterfall' display...You can also just 'auto-tune' your tv and wait until you see something, it prolly won't lock-on, so besure to stay ready to stop the auto scanning and do some manual tuning (also see: Building the transmitter below for more details).
## Software
* this pi image: TODO (no gui/x)
* enable PAL on rpi 1 (sdtv mode 2) in /boot/config.txt
* `$ sudo apt-get install omxplayer`, a command line media player that is designed for HW acceleration on the RPI. Its capable of playing video RTMP streams as well.
* connect to tty1 from ssh:
`$ sudo chmod 666 /dev/tty1`
`$ script tty1`
Playing / streaming youtube videos
NOTE: download / update to the LATEST youtube-dl!!
`$ omxplayer 'youtube-dl -g -f mp4 <youtube-url>'`
(<youtube-url> can also be youtube ID, mind that when your ID has a dash, you must encapsulatethe id with single quotes)
(-f mp4: force mp4 (omxplayer cant play webm))
Analog capable TV with antenna. We used an Amstrad CTV 140 with antenna input.
### Tuning your tv
It's handy to fisrt check your RPI composite output on the AV/AUX channel of your TV using a cinch/rca/tulip cable. It should be crisp and colorful. If so, you can go wireless. Else try to enable PAL on rpi 1 (sdtv mode 2?) in /boot/config.txt
When all is good, you can manually tune your TV to the beginning of the VHF1 band or just use 'auto tune' to find the transmitted signal.
Notes: this transmitter is designed and tested to work on the VHF1, also called 'Band 1' (47 to 68 MHz for the European Broadcasting Area), specifically on 50 MHz, allocated to amateur radio operators ('hams'). The bandwidth of the PAL signal is around 4.5MHz though, and might not be allowed on this frequeny...Also, this transmitter is rather dirty and can possibly transmit on other frequencies (multiples of the base carrier wave). A filter would be good...Trivia: The '6 Meter band' is called the 'magic band' because it shares the treasured porperties of both High Frequency (HF) and Very High Frequency (VHF) radio wave propagation, namely: skywave, meteorscatter and Multiple-hop sporadic E propagation allowing for intercontinental communications at distances of up to 10,000 kilometres.
### Receiving using Software Defined radio
Cheap rtl-sdr sticks dont have enough (4MHz) bandwidth to receive full color pal. Black and white is supposed to be possible using 'TV Sharp': (no sound, atleast not withouth 2 stikcs)!
Find a way to transmit legally on this band: Either look into SSTV (and use computers to receive using a cheap sdr dongle) or look into amateur televisie (ATV) that uses much higher frequencies (thus allowing for more bandwidth...but good luck hand soldering such a transmitter/receiver):
* 3cm (10GHz)
* 6cm (5,7GHz)
* 13cm (2,3 GHz)
* 23cm (1,2 GHz)
* 70cm (434.25 MHz) < might be possible to hand solder...
(ref )
* Filter (see above).
* Amplifier: increase the range of your dirty transmitter...not sure 'ham' radio amplifiers will workbecuase they are mainly focussed on CW, voice or other low-bandwith (far reaching) signals.PALis4.5MHZ wide..and proly not allwed on the band <<< dikke 'space bug' as described here: line 6: (possible amp:
* Sound: there is no sound. Again Kogawa might have an answer:
* put camera on RPI (there are headers no?) I have cameras, and 'live stream'
## LINKS (hacking variable inductor to add audio to your fm tv transmitter) (video tutorial of kogawa fm audio transmitter with nice soundtrack by Dan Abrams (if u want this cd, i have it))