How many coaxial cable feeds do I need?

[linsladeboy]

I am still unsure on what permutation of LNB's and receiver to install when I take the plunge and I am perplexed regarding the issue of cable feeds on units with hard drives.
According to other forums I have read SKY+ BOX needs multiple output LNB as 2 cables have to be connected to back of receiver. Would that be the same for a NON-SKY satellite receiver with hard drive?
The reason I am asking is I was under the impression that terrestrial hard drive receivers were connected to single aerial lead and then used a short loop-through cable to connect to second tuner in the unit .
Could one of you friendly boffins please explain!

[BGonaSTICK]

It's not the hard drive in the Sky+ box that needs the second coax, but the second tuner.

Inside the Sky+ box there are physically two tuners. That's the only way to be able to record one thing while watching another, or record two different things at the same time etc.

A tuner component can only be tuned to one frequency (that's its primary function), so if you want to watch/record two frequencies, you need two tuners and hence two cable runs and two outputs from your LNB.

HTH

[linsladeboy]

Ok Stick I'm with you there!
So I am wrong in thinking that a Freeview hard drive receiver with 2 tuners as in say a Topfield only needs one cable run from aerial?
Why am I so thick!!!

[BGonaSTICK]

Firstly, I should say that terrestrial TV isn't my specialist subject ops: but as far as I'm aware, a single cable would do the job on a 'Freeview with HDD' type gadget.

OK, I'm going to 'fess up now in that I slightly over-simplified my 'tuner' description above so that you could get your head around it. If you have that ticked off in your mind, you can read the next bit!

Domestic European satellite TV typically uses (keeping this simple and ignoring all the odd/exotic stuff) a 'Universal' LNB. This is an active component as opposed to your dumb old TV aerial.

Your terrestrial aerial is just a big scoop which shovels any signal it finds down your coax to your terrestrial device avec tuner. That's not to say it picks up any old frequency regardless, because the elements in the antenna array are tuned by way of length to receive a particular band of transmissions.

A satellite setup works differently. The LNB is actively involved in the tuning and signal selection process, under supervision and control of the receiver itself. There are two adjacent frequency bands used, and two signal orientations. More on this in a mo.

Bouncing around a bit here - with terrestrial, you have Horizonally polarised signals and Vertically polarised signals, depending on which transmitter you have your antenna pointed at. Most are horizontal in the UK, but some are vertical. You can see which is which by looking at the aerial itself. If the elements are laying flat, your local transmitter is transmitting the TV signal horizontally polarised. If you twisted your aerial through 90 degrees so that the elements were all standing up, you would get cr@ppy reception for sure!

Satellite works the same, but the signals on adjacent channels tend to alternate polarisation so that they don't interfere with each other, and so that more can be squeezed into the available spectrum.

How does your dish cope with both? The LNB does it for you, and the receiver tells it which way to expect the signal based on the transponder definition it has stored in the firmware (and which you can manually change) for a given frequency.

So, a quick review. The satellite signal can be in one of four 'states' if you like.

1) Low band, Horizontal polarisation
2) Low band, Vertical polarisation
3) High band, Horizontal polarisation
4) High band, Vertical polarisation

The LNB/receiver combination sorts this out based on which channel you're tuned to, and dynamically switches when you do. Cool.

What the LNB also does is take that really flimsy, weak microwave signal, and knocks a whole heap of frequency off of it.

Now, getting to the bloody point at last (:) it does this in a whole block of frequencies. The LNB (low noise block down converter) down-converts a block of frequencies into what is known as the IF (Intermediate Frequency) which is now at a much more useful wavelength, amplifies it, and pokes it down your coax to the receiver.

See, I told you terrestrial was stupid and boring.

Didn't I?

Oh, well it is

There you go! You're not thick, you just didn't learn this stuff yet

STICK

[Chrisuk]

............and thats why he is admin

[linsladeboy]

Bleedin' hell Stick, you're a satellite genius!!! : :clap:
It all makes sense now!
Have you ever thought of starting a night school on satellite tuition, you'd make a fortune!

[BGonaSTICK]

I thought I'd make a fortune by starting a free satellite forum, but I think my plan was doomed from the beginning due to the fact it was free...

:roflmao:

I'm poor, but I feel good about myself

[alcina]

Methinks this should be a sticky!

Alcina

[BGonaSTICK]

Well, you're the boss in this section ... you can try out some of your new moderator-superpowers.

Let me take a backup first though :roflmao: JOKING!

Perhaps you could rename the thread 'How many coaxial cables do I need?' or something even more obvious so that everyone can tell at a glance what it is. I'm sure linsladeboy won't mind

STICK

[alcina]

Oooh...I feel like God!

Alcina