Aerial cabling for freeview HD

[admin_exported]

How many aerial cables do I need for freeview HD knowing that freesat needs 2 (thats if you need to record one and watch another)?

I havent seen the rear of any freeview HD set top boxes.

I would like to be able to record two channels at the same time while even watching another - is this possible?

Thanks in advance.

 

[Andrew Everard]

Same aerial and single downlead as standard digital or indeed analogue TV, provided the signal strength is OK.

 

[Anonymous]

That means I can watch any channel on freeview HD and record any another channel (provided that the setbox is a recorder) with one cable from my aerial. Sounds good to me.

Why is it with freesat you cant, you must have 2 cables from your dish.

 

[daveh75]

beedee:

That means I can watch any channel on freeview HD and record any another channel (provided that the setbox is a recorder) with one cable from my aerial. Sounds good to me. YesWhy is it with freesat you cant, you must have 2 cables from your dish. Because DTT/Freeview is broadcast using single frequency band/polarisation, so the signal can be easily split to feed two tuners.

Where as satellite uses both Horizontal and Vertical polarisation as well as high and low bands, giving four different frequency bands/modes i.e horizontal low, horizontal high,vertical low and vertical high.

Due to technical limitations, an LNB (part on the end of the dish arm that receives the reflected signals) can only output one band at any one time, meaning that if you was to split a single feed to two tuners,both tuners would be limited to only channels on the selected band.

So for example, if you were watching channel 4(which is horizontally polarised) on one tuner, you then wouldn't be able to record BBC HD (which is vertically polarised) on the other tuner...

 

[Big Aura]

interesting - if there are just 4 'options', does that mean that that with a single LNB, could you watch 1; record another provided they were both, say, "vertical low", or is it still one signal per channel.

Thanks.

 

[daveh75]

Big Aura:
interesting - if there are just 4 'options', does that mean that that with a single LNB, could you watch 1; record another provided they were both, say, "vertical low",Theoretically yes,though in practice it's a pita and doesn't always work.

Using a splitter drastically reduces the signal strength,each leg/output of a 2 way splitter will only output around 40-45% of the input signal, so if you have longish cable runs,the stb has insensitive tuners or there's bad weather you may find you dont get any signal at all.

You also need to consider that the LNB "mode" is controlled by the STB's tuner, the polarisation is controlled by voltage switching between around 13v (for vertical polarisation) and around 18v (for horizontal polarisation) and by sending a 22kHz signal along the cable to switch the LNB into high band.

As you can imagine, two tuners sending current along the cable at the same time can lead to problems.So a splitter that only allows DC pass through on one of it's legs is required,meaning only one tuner controls the LNB and the other acts as a slave.