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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 31st Jul 2008, 8:12 pm   #1
murphyv310
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Default Using multiple aurora's

Hello.
I now have 5 aurora converters and 4 of them are being used on my aerial system. I tried simple capacitance coupling to a distribution box with no end of trouble. I chose the following channels for the necessary spacing Band 1, channels 1 & 5. Band 3 channels 7 & 10. All of the problems were to do with cross mod, I tried attenuation from the Auroras, after coupling etc with no success.
I then had a brainwave (very rare) I wound on a 2 inch ferrite torrodial 5 turns on each band one input and 2 turns on each band 3 input using 18SWG enamalled copper wire, and a further 3 turns of wire for the output. Now I know there must be a bad mismatch but when fed to the distribution amp all is fine, what I did do was to fit an adjustable attenuator in each band one feed to set the level so you don't have to adjust the contrast between band 1 & 3 on the older sets.
I am feeding BBC1 to channel 1, Test card "C" to channel 5, STV to channel 7 & a DVD input to channel 10.
My last aurora is used to make up VHS tapes on 405 but will also be used for my 819 line set.
Trevor
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Old 31st Jul 2008, 9:25 pm   #2
BGmidsUK
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Default Re: Using multiple aurora's

Very interesting thanks. Using a single Aurora at present to feed my Sony portable which has a single aerial input, I find that there are harmonics all over the place and this basically makes it unuseable for a distribution system.

I'm about to set up a 3-channel system using Auroras, but will be restricted to Band I only if I follow my original intention of feeding it into the CATV distribution, as most (if not all) Band III channels are in use. Use of Ch4 is needed for my TV12B Obviously I will have to use adjacent channels if I do this, as I need to leave Channel 1 clear for the proposed BHTG transmissions from Alexandra Palace! Or find 1 free Band III channel .. and I can't guarantee that it won't already be earmarked or in use for digital Cable TV, aside from the different channel spacing ..

In my case it will likely require use of tuneable preamps for each channel, these then fed into a combiner.



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Old 31st Jul 2008, 9:32 pm   #3
murphyv310
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Default Re: Using multiple aurora's

Hi BG.
It looks as if you will have more problems than me, the auroras do produce many harmonics and Darryl does make that quite clear. Weather there is some filtering using the torroid I dont know but it works for me. I am not using my system for UHF or 625 though.
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Old 31st Jul 2008, 10:10 pm   #4
Sean Williams
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Default Re: Using multiple aurora's

It is quite easy to make notch filters, or bandpass filters to sort this issue out - there may even be design tools available on the web
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Old 31st Jul 2008, 11:57 pm   #5
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Default Re: Using multiple aurora's

That's an interesting method you came up with Trevor. I wonder if there is some inherent filtering going on with your coil?

I have used regular RF splitter/combiners to add multiple outputs together, but have been careful in choosing the channels so the harmonics won't affect the main carriers. The output from the Freescale modulators at lower frequencies is not a simple square wave. They modify the shape to lower the odd harmonics at the expense of adding even harmonics. So for example, a video carrier of 45MHz (+/-3MHz for the video if referencing 405) would spread out at 84-96MHz, 126-144MHz, 168-192MHz and so on. This means you should be able to combine this with channels 2,3,4 and 5 without filters.You would not be able to add channels 6,7,8 or 9 without filtering.

FYI: the Freescale RF modulator chip has gone end-of-life. As of next month, you will only be able to get them as long as you can find them in stock somewhere.

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Old 25th Aug 2008, 10:07 pm   #6
BGmidsUK
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Default Re: Using multiple aurora's

I have found that connecting no more than one Aurora, Band I channel is fine, but (without filtering) connecting another Aurora causes a pattern a bit like sparklies on the Band I signal, regardless of the channel the second Aurora is set to.

However, I found that using Channels 6, 8 or 9, and 12 produces good results seemingly free from interference. Channel 13 is also useable but I noticed slight patterning. Therefore 3 channels can be used at once without mutual interference problems, using a simple splitter/combiner unit (such as those used by ntl/virgin, with a 5-1000MHz bandwidth).

There is plenty of signal there .. even when dividing the output from the combiner to feed more than one set!


I've yet to test this setup with my other TVs so will report on the results here



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