problems with high def freeview

[moosegoose]

has any one herd of some problems with the trials of high def freeview in regaurd to the amount of band width they will use. parogon are in the proccess of developing v and h polirization aerial.as this may be the only way to get hd on freeview.if this is true all these nice digital aerials we have been fitting will be redundant.or will we be fitting hd aerials along side the digital ones.

 

[PaulR]

We already use the distinction between horizontal and vertical polarisation on terrestrial signals. The main transmitters are horizontally polarised and repeater stations are vertical. This ensures that we (hopefully!) get the maximum usage of our linited radio frequencies.

I don't understand what Paragon are doing. Do you have any information?

I don't know for sure but I'm fairly certain that HD will be in MPEG4 which is more efficient in compressing a signal than MPEG2, as used for SD digital. As a result HD occupies almost the same bandwidth as SD.

 

[moosegoose]

acording to the source of my infomationb there a problem fitting it into the 8 mhz slot. there for are considering v and h pol from the same transmitters to over come the problem.as you say there should be no problems. but real world tests have proved otherwise.

 

[PaulR]

Ah, now I understand. What they mean is transmitting both vertical and horizontal components so that it doen't matter whether your aerial is H or V.

Most (all?) FM radio stations have done this for some years now to cater for home aerials which are traditionally horizontal and cars which are vertical.

 

[moosegoose]

i presume digital freeview on horizontal and digital high definition on vertical.which means additional aerials or a aerial with both which is in development.

 

[Llew]

or a aerial with both which is in development.

Interesting. Any info on this moosegoose?

Maybe some control of polarity will be needed in the STB as the aerial presumably will need to be switched between H & V?

Llew

 

[rolfw]

Well that would be a popular move. . . . . I can just hear the phone calls now.!

 

[PaulR]

I still think some information is missing here. I've been to the Paragon website but as I'm not a registered member can't get any information. Looking at their products on the SCC site I don't see anything special there (apart from the rather delicious 1.2m parabolic!).

Adding Horizontal to Vertical doesn't give an extra amount of information sent. It will surely only increase the likelihood of good reception.

Can you be a bit more specific Mongoose.

 

[Channel Hopper]

Who knows, they might plum for circular polarisation :-googly

 

[2cvbloke]

Who knows, they might plum for circular polarisation :-googly

How in the monkies would that work??

 

[PaulR]

Circular polarisation can be imagined as a dipole aerial transmitter that rotates once for every cycle of frequency. Therefore there's at least sometime during the rotation when the receiving horizontal or vertical aerial will be in line.

I think the loss in strength is 3dB but the gain is that, as long as the aerial is pointed in the right direction, then there will be a constant signal.

 

[Llew]

OK if the receiver is just for HD, but presumably it'll be a combined HD/SD box, in which case it'll need to be able to switch polarities.

If an aerial is definitely being designed for combined H/V transmissions, then presumably the STB manufacturers are working on this.

All conjecture though until anything more is known.

Llew

 

[rolfw]

I'm not sure why there would be a need for switchable polarities, I can't see the advantages.

Digital signals, can sit on adjacent channels of the same polarity.

 

[Llew]

But surely the receiver will then only see half the channels in the mux?

The LH and RH polarities received by the circular aerial have, as with H and V, got to be somehow recognised by the STB.

Llew

 

[j..m]

I have been trying to adapt my chimney to accept a horisontal polarisation antenna ..... However the bricks keep falling off & bouncing down to floor level ...... Maybe I should construct a horisontal chimney on the ground & kinda carry it up & mount it ? .... Woddo ya think ? :-tree

 

[2cvbloke]

I have been trying to adapt my chimney to accept a horisontal polarisation antenna ..... However the bricks keep falling off & bouncing down to floor level ...... Maybe I should construct a horisontal chimney on the ground & kinda carry it up & mount it ? .... Woddo ya think ? :-tree

Have you tried just turning the aerial on it's side?

 

[j..m]

Now ya just being silly

 

[2cvbloke]

Now ya just being silly

Sillier things have happened, like satellite dishes on their sides and upside down dishes, plus to make an aerial Horizontally polarised, you turn it 90 degrees from vertical...

 

[j..m]

Ya can do tha "Ye olde" lie the dish on its back trick tho ....... Or am I thinking of summink else :-MrsC

 

[2cvbloke]

Ya can do tha "Ye olde" lie the dish on its back trick tho ....... Or am I thinking of summink else :-MrsC

There's the upside-down method too, I've not tried it yet...