My first dabble with ATV in August 2005. I received these pictures between 27th and 29th August 2005 on 23cm.
This was quite impressive because:
- It was the first time I'd fired the kit up.
- GB3VR is based in Worthing and my QTH was New Milton, about 70 miles.
- GB3IV is on the Isle of Wight and you'd think the signal would be better than Worthing. I think that there is a big hill on the IOW breaking the line of sight.
- GB3VR - Worthing: http://www.videorepeater.co.uk/wvrg_gb3vr.htm
- GB3IV - Isle of Wight: http://www.ukrepeater.net/repeaters/gb3iv.htm
Based on the G1MFG 23cm ATV boards. I have chosen to mount these in a nice 19 inch rack case that I found at a rally. I have found a microwave relay, and plan to make my own control pcb that will allow both the transmitter and receiver to be programmed as well as control the RX/TX sequencing, and also allowing computer control.
The schematic for the controller is still in design, but I am quite happy so far. The circuit is based around a PIC16F873 microcontroller, and will have am RS232 interface for computer control, and an LCD display. I have some nice rotary shaft encoders kicking around, so I have decided to use one for frequency selection. The other functions of the circuit are relay switching, and transmitter and receiver power switching.
- 70MHz QPSK Modulator: http://jf.fourcadier.pagesperso-orange.fr/haut_debit/QPSK2/schema.htm
- DATV Boards: http://www.lechner-cctv.com/d-atv-dvb.151.en.html
For digital television transmission the symbol rate calculation is:
- symbol rate in symbols per second = (Data rate in bits per second * 204) / (188 * bits per symbol)
The 204 is the number of bytes in a packet including the 16 trailing Reed-Solomon error detection and correction bytes. The 188 is the number of data bytes (187 bytes) plus the leading packet sync byte (0x47).
The bits per symbol is the (modulation's power of 2)*(Forward Error Correction). So for example in 64-QAM modulation 64 = 26 so the bits per symbol is 6. The Forward Error Correction (FEC) is usually expressed as a fraction, i.e., 1/2, 3/4, etc. In the case of 3/4 FEC, for every 3 bits of data, you are sending out 4 bits, one of which is for error correction.
For QPSK the bits per symbol is 2.
- given bit rate = 18096263
- Modulation type = 64-QAM
- FEC = 3/4
- See: http://en.wikipedia.org/wiki/Symbol_rate#Digital_television_and_OFDM_example
- Also: http://www.w6ze.org/TechTalk76-DATV.pdf
- And: http://www.atco.tv/Symbols.aspx
ssh firstname.lastname@example.org (d...) asimon cd /root/master-2.7.1 make make install modprobe dvbm chmod 777 /dev/asitx0 chmod 777 /dev/asitx1 asimux-start asimon
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