Can anyone confirm whether the local multiplex in London on Channel 29 is being transmitted from Crystal Palace along with the others or is it being transmitted from Croydon. I did read somewhere it was Croydon but I am not convinced.
And I think my reception improved when Croydon was switched on as I understand one transmitter effectively reinforces the other.
It is usually called SFN ( single frequency network).
It is one of the many wonders of the technology of COFDM digital TV modulation .
Invented by the French (Thompson).
As usual a much better TV broadcast system than the digital TV broadcast system across the pond, (they always get it wrong) , NTSC (pooh) , VHS ,compared to Betamax (yuk)
Croydon only sends a beam to the South, it's just a hole filler I think for the local area, CP looks after the main signal for most of the service area
The real cause of the problem is the girth of the tower at the height the antennas are mounted .
To provide coverage at 360 deg coverage ,it needs a cluster of panels all around the large girth of the tower .
This then will cost a very large amount as to achieve the correct antenna gain needs a enormous amount of panels .
However our monopoly supplier should supply what is required to provide the correct coverage.
What should have been done is configuring the main broadcast antenna to accommodate the input of a local TV multiplex.
With the correct design ,beam tilt and diffrent power levels over 360 deg ,it could ensure full compliance with the antenna radiation mask and provide better coverage .
I am afraid in my opinion a bit of bad engineering yet again is what we have here.
Comments
It is usually called SFN ( single frequency network).
It is one of the many wonders of the technology of COFDM digital TV modulation .
Invented by the French (Thompson).
As usual a much better TV broadcast system than the digital TV broadcast system across the pond, (they always get it wrong) , NTSC (pooh) , VHS ,compared to Betamax (yuk)
Croydon only sends a beam to the South, it's just a hole filler I think for the local area, CP looks after the main signal for most of the service area
It's to minimise overspill to the south - IIRC Crystal Palace is pretty much limited to North, East, and West - it also operates at 20kW.
Croydon on the other hand is 4kW from a lower aerial (219m vs 237m) so can put more of it's signal to the south without excessive overspill.
As a comparison - COM 7 from Crystal Palace is 324m @ 43.1kW and the average 1-6 is 319m at 200kW.
(All heights are Site Height + Antenna above AGL)
So there is a null to the south ...
Whilst Croydon has stacked shrouded yagis to fill in the gap... http://tx.mb21.co.uk/gallery/gallerypage.php?txid=1259&pageid=2118
So there is a null to the south ... As the mast is in the way
Whilst Croydon has stacked shrouded yagis to fill in the gap... http://tx.mb21.co.uk/gallery/gallerypage.php?txid=1259&pageid=2118
The real cause of the problem is the girth of the tower at the height the antennas are mounted .
To provide coverage at 360 deg coverage ,it needs a cluster of panels all around the large girth of the tower .
This then will cost a very large amount as to achieve the correct antenna gain needs a enormous amount of panels .
However our monopoly supplier should supply what is required to provide the correct coverage.
What should have been done is configuring the main broadcast antenna to accommodate the input of a local TV multiplex.
With the correct design ,beam tilt and diffrent power levels over 360 deg ,it could ensure full compliance with the antenna radiation mask and provide better coverage .
I am afraid in my opinion a bit of bad engineering yet again is what we have here.