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Television Standards Converters, Modulators etc Standards converters, modulators anything else for providing signals to vintage televisions.

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Old 18th Feb 2013, 1:34 am   #1
Redders03
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Question Recreating Analogue 1-5

Hi all, I was recently now thinking about how useless the tuners are on all my VCR's and had a though, you can obviously provide one Chanel in analogue by using a freeview box with an RF Modulator but only one signal is produced at one time. Unless you string 5 freeview boxes together and that isn't exactly small and most the output frequency channels are fixed on the boxes.

My question is, does a box exist or one be created that takes freeview channels and converts them into analogue signals all in one go. So Chanel 1-5 recreated once again. The ability to have other channels that could show tests cards would also be a great idea.

Not a necessity just a wondering thought

Thanks
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Old 18th Feb 2013, 2:47 am   #2
paulsherwin
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Default Re: Recreating Analogue 1-5

There are some commercial modulators which will do this, designed for use in places like hotels and hospitals. Not cheap though, and probably OTT for a domestic installation.
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Old 18th Feb 2013, 8:26 am   #3
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Default Re: Recreating Analogue 1-5

One problem is that the simple modulators in domestic equipment are not as well filtered as the original transmissions and so produce more harmonics and larger sidebands. This makes using more that a couple of frequencies difficult as interference problems between them soon build up. You could of course build the necessary filters yourself but designing them for UHF is not a trivial task.

If you want to run a parallel system of aerial wiring (e.g. you don't want to distribute off-air DVB through the same outlets) then you may be able to get away with it, the Labgear MOD111 UHF modulator is supposedly suitable for daisy-chaining together for multiple frequency operation.
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Old 18th Feb 2013, 9:49 am   #4
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Default Re: Recreating Analogue 1-5

If you're making a group of modulators, you don't have to cluster them as tightly as the old analogue transmitters used to be. You can spread them out across the full band. You don't have to fit them all within the bandwidth of one aerial group, you don't have to stagger channels with adjacent service areas.

So you should be able to get away without vestigial sideband filters.

Cheap modulators with drifting carrier frequencies and poor quality are a different matter. As Paul says, there is an established industry making cable TV head-ends for in-house use in hotels etc. I remember a trip to see a spectrum analyser customer with a small business distributing the component modules and his showroom was full of demonstration rigs. Definitely one of the nicer field-trips. He's based in Annecy. Set top boxes are almost junk nowadays to many consumers, it''s good modulators which are pricey.

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Old 18th Feb 2013, 4:32 pm   #5
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Default Re: Recreating Analogue 1-5

It's probably a non-starter but I had thoughts on this a while back.

Would it be possible to switch between tuning points at high speed using a suitable device?

I.e. say you want two channels simultaneously and one uses 20V to tune to that channel and the other channel needs 16V to tune to that one, then a device is used to switch at high speed between the 20V and 16V. If the speed were high enough the switching wouldn't be seen.

I understand that such a 'frequency hopping' system was used in the military a while back.

Obviously there are a myriad and one other factors to consider such as any PLLs needing time to lock up between switch states.
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Old 18th Feb 2013, 6:10 pm   #6
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Default Re: Recreating Analogue 1-5

An alternative to several Freeview boxes and to avoid the cost of an expesive "hotel" unit.
The original Sky Digiboxes can often be found 2nd hand very cheap or free, as many people went over to newer boxes with hard disks, and then to High Definition boxes. They all have an RF modulator and the output frequency can be changed. 5 of them fed from a multi-output LNB might be a cheap way to get all five channels back in analogue.
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Old 18th Feb 2013, 6:19 pm   #7
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Default Re: Recreating Analogue 1-5

Yes thats a good idea why didn't I think of that !
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Old 18th Feb 2013, 8:51 pm   #8
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Default Re: Recreating Analogue 1-5

I was thinking about this last year, around switchover time. I was thinking on the following lines;
A traditional TV tuner has a local oscillator which runs at about 39Mhz above the frequency it is tuned to receive. This local oscillator signal leaks up the aerial cable and is what the detector vans pick up. (its easy to see this signal, just use a double ended coax cable to connect the aerial sockets of two analogue TV's together. Tune one to say ch.22, and start tuning the other one, a blank signal will be recieved around ch26/27 on the second TV). Tune 4 buttons to 4 different frequencies, use a UHF tuner with a microcontroller such as an Arduino to poll the 4 corresponding frequencies fed back up the co ax to determine which button is pressed, using the tuners agc line to detect the channel at which the local oscillator signal from the tv is present, set a i2c controlled modulator to the base frequency of that channel, and issue the IR remote control signal to select the relevent channel on a Freeview box. Hey presto, 4 different channels selectable by 4 push buttons. This hasn't as yet made it into anything further than a thought process though.

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Old 23rd Mar 2013, 8:25 am   #9
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Default Re: Recreating Analogue 1-5

I have done some tests with an old Sky box, the RF output passed through an amplifier and then to a standard TV aerial. Using my Casio handheld TV set, I could watch the signal all around my house easily on channel 21, but when on 68, the signal is much less.

My ultimate aim is to re-create analogue 1-5 as well, but I may use the lower channels as the range seems better.
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Old 23rd Mar 2013, 8:59 am   #10
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Default Re: Recreating Analogue 1-5

Of course, I don't intend to completely re-create the situation whereby 1-4 was a good picture with 5 snowy!!
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Old 23rd Mar 2013, 12:58 pm   #11
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Default Re: Recreating Analogue 1-5

I have a situation here where I am combining 1 and 9 on 405 from 2 auroras and one modulater producing analogue on 625 channel 33 so I can recreate television as it was in the London area in the 1960s .
Incidently , this is the same as we are hoping to produce at the wireless museum too .
Redders , feel free to send me a PM and pop round to see how I have done it !
regards
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Old 23rd Mar 2013, 3:14 pm   #12
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Default Re: Recreating Analogue 1-5

I thought about relaying BBC1, BBC2, ITV, CH4 and CH5 analogue around the house a few years ago when Mendip analogue switched off. I had it all planned out as to where I was going to fit the Freeview STB’s with RF modulators and the UHF channels that I would use. Sadly I never got around to completing this project.
But it is an interesting idea and should work well providing you were careful with the choice of RF channels. To avoid any interference you would obviously have to avoid the local Freeview channels plus the RF output channels of VCR’s etc and then there is the image clash to be considered. This means avoiding all channel spacing +/-5 and +/-9. But as modulators are double sideband to completely avoid any risk of potential clashes I suppose you would have to avoid spacings of +/-4, +/-5, +/- 6 and +/-8, +/-9 and +/-10. This could be problematic in areas where there is more than one group of Freeview channels and of course there is the future 4G use of the 800Mhz band to be considered.
I have decided to use just one extra Freeview box fitted with a modulator to feed our two serviceable VCR’s which means only finding one spare channel and switching it on only when required. To avoid leaving the extra Freeview STB box running on standby for most of the time I will have to split and combine the signal which should not be a problem as we have a very strong Freeview signal from the might Mendip transmitter.
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Old 24th Mar 2013, 1:21 am   #13
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Default Re: Recreating Analogue 1-5

I have 5 Sky boxes now up and running,iam using 21,31,41,51,61,and it is working nicely,picture perfect,no problems at all!
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