DX TV has been a hobby since the early seventies when as a young lad growing up in Mid Wales I would visit the shack of a local radio amateur 'Bert Mills' GW3LJP and wonder at the many sides of this hobby.For many years I would spend every sunday afternoon walking up to the highest point in our local village of Crossgates in Powys where Bert was a caretaker of the local chapel. I remember the first time I saw colour tv on a small noisy picture of a Sony triniton - it was the African Queen Film. Now bear in mind in our neck of the woods we only had BBC Cymru/Wales on channel 1 405 black and white and here I guess is where my first sort of DXTV came in where bert had given me a band 1 antenna 4 ele with the match rods which you could adjust. I put this on a pole up the garden and could just get a watchable picture on channel 4 for the full english which had .........The Goodies show in mid week. Ok so maybe not real DX but soon to come was a dual standard set which Bert showed me how to break the line switch and get VHF tuning and 625 line scan....I was only 11 years old and tinkering already much to the dismay and careful eye of my parents. Soon TVE was romping in and many saturdays were spent watching the bullfighting.
It was all this which obviously steered my career in Radio and Electronics through various part time in HM Forces Sigs and main time Satellite comms which I am now into my 31'st year. Having seen Analogue come and go and various 'ever clever' compression techniques push discrete components further and smaller into that black box I can still honestly say I get no more kick than hearing the roar of the Vestigual sideband carrier rising out of the noise....and then dissapearing again.
My past years have been taken up with lifes usual activities and then a few years ago decided to feed the 6 Metre beam into the analogue tuner of the 42 inch plasma in the Lounge ( much to the dismay of the other half this time who also seems to keep a watchful eye over me) Had great fun watching suprisingly good full colour pics for the last few years including Iceland one evening. So I thought it was time to dust off the receiver. I had already been monitoring E2/R1 on a TS2000 for 6 meter openings.
In the early 80's I built a scanning DX TV receiver which was basically a varicap tuner where the scanning part made of logic had preset channels to give the voltages required for R1 E2 etc and the composite video fed via some filtering to a 15625 Hz detector (NE567 PLL) this would stop the scan when video was detected and give a beep alarm. After much messing with the video filtering it would detect video before you could even see any change of noise on the screen.
I am on version 4 now which obviously has switchable IF filtering and lcd channel display which scans locks out on detect etc etc ( all discrete logic as I have to go begging my colleagues to write a pic chip prog which is in hand.) Even the LCD channel display in V 3.0 is done with a diode matrix and still going well with dc biasing.
This is a messy prototype of version 2 ( why do they always make it to the final version !! )
The top adjustment pots select the tuning voltage for any varactor tuner. With the addition of the video detector it can be encorporated to complete a scanning receiver.
The detector makes it a very good early warning and the video can obviously still be fed through to Dscaler and the likes..
If anyone wants specific circuit details please contact me.
The display unit can also be as simple as a row of LED's it's really not needed.
Logic comprises of a clock, a decade counter and many analogue swiches. A problem is you have a max of 12 V Tuning adjustment for the varicap although this will take you well up above 90 Mhz so not really a drama.
Here are a few pics below from this week of Syria on E2, freq offset was comparable but luck enough to see the testcard (no logo) go to a waving flag which looks like Syria.
I don't know if Bert is looking down now but I do know he'll have a receiver running somewhere.....It'll be a sad day when band 1 Analogue falls silent of that faithfull hum ..I intend to use the last years to the full !!
Ian Collins G8ZVZ iancol@fotoesque.com ........http://www.weatherpictures.co.uk ..............http://www.icpic.co.uk
Band 1 Home brew DXTVscanning RX ( luxor tv board+Tuner,modified if filtering), 6 metre 5 ele beam pre-amp+ a lifelong interest :-)
Sony SB920 + narrow fitering FM DX
