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Forum 141

Tech Chat Antiference XP6

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crustytv
(@crustytv)
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Hi, I've been rummaging in my stores and found a box of aerial distribution parts such as splitters, plugs, amps, VHF/UHF Tele-vertas, and I found this (see below). It's stumped me, it only has one in and one out, but six other possible connections. Are they inputs, outputs, anyone encountered one of these before, and if so what the intended use would be?

It mentions 'Tee Unit', still means nothing or how you would use it with regard to connectivity.

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Posted : 13/08/2023 4:17 pm
Lloyd
(@lloyd)
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Strange looking device! At first it looked a bit like the things I use for RF distribution around the shed, just a splitter.. What happens if you connect a few things to it?

 
Posted : 13/08/2023 4:46 pm
Cathovisor
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From memory, these sort of things are fed with a high level signal and then lower level outputs are taken from the tap points - but they can be cascaded, hence the in/out connections.

Have a look at the likes of https://www.blake-uk.com/distribution-metal-taps-split.html for a current equivalent.

 
Posted : 13/08/2023 8:09 pm
crustytv
(@crustytv)
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Thanks, Mike, another excellent resource. Now I think I may have solved my problem of adding a third modulator to my RF system, and the interference it causes on the two existing channels. It looks like I need an Overlap Blocking Filter.

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Posted : 13/08/2023 8:46 pm
Cathovisor
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Once upon a time you could get charts showing where you'd run into trouble with modulators running on close channel numbers - and it's not helped by the modulators being DSB rather than VSB. It's a bit of a science and sadly, we don't have Terry's guidance on such matters now.

However, I dare say resources may still be out there to guide us.

 
Posted : 13/08/2023 9:23 pm
irob2345
(@irob2345)
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For each modulator you need a bandpass filter with a trap for the unwanted sideband to make it VSB.

I used to make these for VHF and tune them using a spectrum analyser, using the tracking generator output feeding the input to the filter. The Marconi SA I used only went to 120Mhz so it was only useful for bands 1 and 2 (we used to use Band 2 in Oz for TV!), but it did go down to DC.

The design and construction of UHF filters is more challenging.

These days, the way I'd do it is run the modulator at TV IF frequency and use a SAW filter. Then frequency convert it to your desired UHF channel with a PLL. Kinda using a TV tuner backwards,

 
Posted : 14/08/2023 9:21 am
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