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Television Standards Converters, Modulators etc Standards converters, modulators anything else for providing signals to vintage televisions. |
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15th Apr 2006, 11:39 pm | #1 |
Octode
Join Date: Mar 2006
Location: Co. Durham, UK.
Posts: 1,117
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"If you were a crank...."
Hello,
Just been reading about the 'Vest Pocket' Aurora. One of my many 'impossible' schoolboy inventions was a tobacco-tin sized 'plug-in' which went between the aerial downlead and the set, and let you get BBC2, like the posh kids! Yesterday's science fiction.......! More seriously, If you were a crank, and you had the correct period recorded programmes from both BBC and ITV, and seperate machines to play them simultaneously, would it be possible to use a pair of the new budget-priced Auroras, together with attenuators and a band I/III diplexer, to create the effect of 'turning over' to see what was on the 'other side'? You would have to be a crank, of course! Cheers. B. |
16th Apr 2006, 7:27 am | #2 | |
Retired Dormant Member
Join Date: Dec 2003
Location: North London, UK.
Posts: 6,168
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Re: "If you were a crank...."
Quote:
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16th Apr 2006, 11:49 am | #3 |
Retired Dormant Member
Join Date: Dec 2003
Location: Solingen, Germany
Posts: 727
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Re: "If you were a crank...."
Hi,
guess why I use these complicated filters at the output of my modulators. But I sadly learned that noise in the picture is well accepted on an old set. Kind regards Darius |
16th Apr 2006, 1:08 pm | #4 |
Retired Dormant Member
Join Date: Jul 2005
Location: West Yorkshire, UK.
Posts: 1,700
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Re: "If you were a crank...."
Hi,
Flying dangerously close to drifting OT, here; but still staying within the general theme of "having several 405-line VHF channels rather than just one" I have a moderately insane idea... With an indecently rapid PC and some hacking about with the software it wouldn't be impossible to fit three tuner cards in a PC. Theoretically one can then arrange to have the three image streams from the cards greyscaled then combined into one colour image such that one channel is in red, another is in green, and the third in blue. Then you just need to add the syncs seperately to the three RGB card outputs; feed each of these three now composite monochrome outputs to three modulators set to different channels... Don't expect me to demonstrate this anytime soon; I have plenty of other mad ideas to be getting on with for now and there's only one of me, only 24 hours in a day, etc., etc. Regards, Kat |
16th Apr 2006, 1:28 pm | #5 |
Retired Dormant Member
Join Date: Dec 2003
Location: North London, UK.
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Re: "If you were a crank...."
Kat, doesn't sound too implausible to me.
The approach that Darryl and I discussed some time ago (and I think some of it was in the forum too) was direct digital synthsis at the final RF carrier frequency. This can do multiple channels without any fundamental problem except that as you get above band 1 the digital clock frequency gets a bit impractical. I suppose you could synthesise at a suitable IF and heterodyne the whole lot up to RF. The conclusion we reached was that it was almost certainly technically feasible but a whole lot more work than any of us reckoned was worth it. |
16th Apr 2006, 6:25 pm | #6 |
Retired Dormant Member
Join Date: Dec 2003
Location: Solingen, Germany
Posts: 727
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Re: "If you were a crank...."
https://www.vintage-radio.net/forum/...ead.php?t=2837
Good evening, I think the London- Birmingham modulator is the ultimate solution. It makes all 405 sets working without any switching. The only complicated thing is the filter, but until now I haven't seen any modulator that don't need a filter. The axing modulator uses the MC44B_373 and has a switched filter banch at its output. Not good but much better than nothing. Darius |
16th Apr 2006, 6:34 pm | #7 |
Dekatron
Join Date: Feb 2005
Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW
Posts: 3,518
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Re: "If you were a crank...."
The DDS idea is a good one, and with a fixed crystal oscillator and mixer on the output you could generate band 1 and 3 signals fairly easily, you do still need filtering, which becomes complicated when you have to change frequencies so far apart - simple at up to 30Mhz, but into VHF the additional inductance and loss is not so acceptable.
There is no reason why the modulator Darius has designed cannot be converted for ch2 or 3, the one I have built does channels 1 and 3 at the same time, however, there are some very strange mixing products on the output! No real need for things to be so complicated Cheers Sean
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Engineers make things work and have spare bits when finished |
19th Apr 2006, 3:30 pm | #8 |
Tetrode
Join Date: Aug 2003
Location: Cambridge, Cambridgeshire, UK.
Posts: 91
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Re: "If you were a crank...."
I wonder if it would be possible to use one of these - http://www.gnu.org/software/gnuradio/ - to generate the signals? With some very clever software could you can take an off air signal with one daughterboard (maybe a couple of channels in a digital boquet?), convert them to 405 and then generate the relevant Band I/III signals?
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