Aerial feed to tv

[everthewatcher]

FWIW the attenuators were F connector ones left behind by Virgin Media. One was found in the street.

They're 'forward path' ones that attenuate only in the forward direction i.e. cabinet to the modem, used to optimise the received signal level, and the return path from the modem is unaffected. They cover far more than Bands VI &V and on the basis of this test seem to be quite accurate.

 

[Black Hole]

They're 'forward path' ones that attenuate only in the forward direction i.e. cabinet to the modem, used to optimise the received signal level, and the return path from the modem is unaffected.

Wow, that's clever (unless upstream and downstream use different frequency bands).

 

[everthewatcher]

Wow, that's clever (unless upstream and downstream use different frequency bands).

I thought it was going to be some variant on the telephone hybrid coil, but it seems they use different frequencies - downstream >88MHz, upstream <65MHz.

Here's a link https://en-gb.technetix.com/products1/product/140-forward-path-attenuators

 

[Trev]

But TVs don't work anywhere close to those frequencies as you know.
If they obviously attenuate 88MHz one way, I wonder what they do to 600(odd) MHz the other way around?

 

[everthewatcher]

But TVs don't work anywhere close to those frequencies as you know.

Do you know what < and > mean?

 

[Trev]

Yes, but I still can't get my head around how they work directional.
So, out of interest, what does happen attenuation wise if you reverse it?

 

[everthewatcher]

Yes, but I still can't get my head around how they work directional.

Ah, I see.

I initially thought the 'forward' part referred to direction relative to the filter. But it doesn't, as a look at the datasheet makes clear.

'Forward path' refers to the frequencies used to transmit stuff in the forward direction, i.e. downstream, which presumably are in the band 88-860MHz according to the datasheet, and it's only these frequencies that are attenuated.

The slower reverse/upstream stuff is carried on frequencies below 66MHz, which will go through the attenuator with only a 1-1.5dB loss, again according to the datasheet.

And of course 88MHz to 860MHz covers Band VI and V and a lot more (which is why they're hot on screening, having F connectors tightened properly and fitting terminators on unused cable ends.

So, out of interest, what does happen attenuation wise if you reverse it?

They'll work just the same - frequencies above 88MHz will be attenuated, those below 65MHz won't.

 

[Black Hole]

Yes, but I still can't get my head around how they work directional.

Neither can I, unpowered.

 

[Trev]

What about a HPF with attenuator in series and a LPF with no attenuation in parallel with that lot? Would that fly?
Must be something like that.

 

[everthewatcher]

What about a HPF with attenuator in series and a LPF with no attenuation in parallel with that lot? Would that fly?
Must be something like that.

Yes, that's what it effectively is, although how it's implemented I'm not going to investigate - it's soldered closed and I've never got into RF stuff.