Friday, 9 January 2015

Workshop video rack.

Whilst I don't get as much time as I'd like to "play tellys", the state of the workshop video sources has been plaguing me recently.

For those outside the UK, I'll explain a little. All TV transmissions in the UK are now digital. They're delivered in Band IV UHF.

In times gone by, there used to be a 405 line black and white only service (System A). This existed  from 1936 until 1984 and started out in Band I VHF, and then expanded into Band III when ITV started in 1955. 625 lines (System I) was introduced for the start of the BBC2 service in 1964, in UHF only (it went colour (PAL) in 1967, and all services moved to UHF 625, both in bands IV and V (Band V has now been flogged off to the mobile phone operators for 4G etc.) )

Now, to run my old tellys we need to generate at least some of these signals. The UHF 625 line colour stuff is easy, just get a DVB receiver (Freeview) with a modulator built in. 405 lines is a little more tricky, but thankfully there exists a small box called an Aurora, which is a 625 line to 405 converter (there are other types available too, to convert between almost anything!)  with a built in VHF modulator. It's superb. Auroras (Auroae?) can be found here. If you are inside the EU, you can order them from Crowthorne tubes here.

The big problem is this motly collection  of boxes and power  supplies, the odd DVD player etc, has just been jury rigged as required. Not a satisfactory situation.

So, I designed myself a little rack to house it all.

 All connections are made on the front panel. This is a workshop piece of equipment, and you don't want to go fiddling around the back. The signal from our aerial (with our digital TV signal on) feeds the top Belling Lee socket, this is passed to a "4G" filter to remove any signals from band V. The RF then feeds the two freeview boxes and the outputs from these (in Band V) are mixed and sent to the mixer in a UHF modulator. The band I output from the Aurora standards converter feeds an attenuator (it's output is hot!) and a low pass filter, this is then combined with the UHF RF and passed (finally!) to the lower Belling Lee locket for connection to the set or sets.

Video to the standards converter is switchable from nothing (which causes the Aurora to output test card C), the Aux input sockets on the front, the DVD or either freeview receivers. Video to the UHF modulator can be switched from the Aux sockets or the DVD player (The freeview is already modulated)

 Much neater and I'm rather pleased with how it's all come out.

I've subsequently added a small Sumvision Cyclone media player to the set up, which is great for playing video files and test cards from a USB memory stick.

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