Celestial TV

[Vertigo]

Now I've got one of those and never considered using it like that - I shall have to have a play with it. I can just about get reception of one or two radio channels here; Radio 4, thank goodness, and just about classic FM, but not really acceptably, and that's with an external FM aerial mounted on the roof plus booster. We can't get terrestrial TV at all in the village and had to have a relay station up on the hill. After that was taken out by lightening and then battles with the insurance people meant it stayed out for several months pretty much everyone in the village switched to Sky. I already mainly listen radio channels in the evening. Only problem is that the sound quality is pretty dreadful (heavily compressed I suspect and with the top and bottom frequencies fairly seriously truncated). When I had both the terrestrial TV (via the repaired relay on the hill) and Sky it was interesting that the terrestrial picture was much worse than the satellite one but the terrestrial (analogue) audio was far superior to the Sky one.

 

[Ray McCarthy]

Audio on all sat channels is compressed some too much. DAB is even worse as bitrate is typically half that needed so the cost is halved. DAB+ is slightly poorer as they use it (where it exists) to fit twice as many stations in, not for more quality.
Modern TVs have rubbish speakers that accentuate poor audio.
Analogue TV sound was Mono HiFi FM. Terrestrial Nicam was a near CD quality digital stereo system simply in parallel to the Analogue transmission. Satellite & Terrestrial Digital audio can be any quality they pay for.
Not all stations are same compression, some are better.
Compare Jazz FM, Gold, Lyric FM, BBC R3, BBC R4, BBC R2
Gold and Jazz FM are likely poor.

For the Free TV & Radio, Sky and Freesat share EXACTLY the same signal. Some Sky boxes may not have high quality analogue out, if old and PSU capacitors wearing out.

 

[Vertigo]

Back when I was comparing it was a brand new Sky box. I noticed the difference when watching the Proms on BBC and elected to watch them on the terrestrial as it sounded so much better and the snowy picture didn't matter too much for that!

 

[Ray McCarthy]

The extra compression. Sickening. BBC bean counters.

 

[chrispenycate]

The only time I got mixed up with satellite transmission was during the Ski World Cup in - oh, early nineties, I suppose so lots will be different now. The parabola was probably a touch less than two metres, and yes, it was motorised, and it was carrying five individual camera channels (patched up for each race), final mix, preview and insert text, clean picture without keying or text, twenty-four audio channels plus talkbacks in several different languages, return of three Swiss TV channels, remote picture from a helicopter - and the 4X4 it was mounted on had been carried up the mountain below yet another helicopter.

The truck with all the switching and camera remotes was a lot lower down, actually on the road, with a seriously chunky multiway cable between the two (I suppose nowadays it's all digitally multiplexed?) and watching the guys manhandle that between the two was very amusing (one suspects that actually doing it was less so - couldn't they have left one end connected when going up with the 'copter?), and into the truck came the huge mass of triax camera cables, mic distribution boxes, ill defined RJ45 cables, three phase power and optical links, lighting controls…

Unfortunately, as a mere sound specialist I didn't need to understand any of this, and was quite well occupied, so didn't pick up much.

 

[Ray McCarthy]

I used to go to Anga (just started for 2015 today in Cologne/Köln) and IBC Amsterdam up till 2008. Lots of juicy Satellite OB trucks, esp at IBC. IBC is HUGE!
On my last Anga trip I persuaded various Chinese & Turkish vendors to part with stuff (I did pay) that I wanted to experiment with. I took it as carry-on to plane. Airport security was bemused.

In 1970s the BBC needed an emergency Scotland - N.I. link and took a terrestrial Microwave Link up a suitable Co. Antrim mountain. They "lost" a landrover temporarily in the snow.

The US news crews in Belfast brought their tapes in and we sent them via Eurovision/EBU/BBC terrestrial microwave to Spain, the Earth Station there tracked a satellite for the Transatlantic hop.

I was only on OB a few times, and there was no satellite links in those days for OB.

For Sport OB the big dish on an Artic. or Landrover was pointed at top of Divis TV mast for the one way Analogue FM video link + one sound channel. Additional Sound / Talk back by GPO lines, if available. It had only ever been used for sport, but on one occasion in 1978* they tried their first live news link from a hostage situation just off Malone Rd. By the time we had the link up it was all over!

[* I think 1978]

 

[chrispenycate]

I found it amazing they could do full duplex on one dish. I mean, microwatts or picowatts on the receiver, tens of watts on the transmitter and both of them as close to the focus point as you could put them – I'd have expected the receiver element or head amp to be completely swamped.

 

[Ray McCarthy]

I found it amazing they could do full duplex on one dish

Completely different bands!
Uplink might be 14GHz+ on an 11GHz downlink, About 2GHz to 4GHz TX/RX offset (2000MHz to 4000MHz)
Also alternate polarisation.
The coupler behind horn splits/joins the polarisations.
Then there is a MECHANICAL (I kid you not) passive filter, well, it's just basically a clever piece of aluminium.
Then the RX LNB has only one polarisation, unlike home TV and better strip line filters.

I can post photos of all the parts except the Transmit Power Amp of the ODU (Out Door Unit), I don't have one.
I've had 3 systems here on test in the past.

Earlier systems time compressed the data and ran half duplex to give appearance of full duplex.

My Broadband connection is 10.2GHz downlink and 10.65GHz uplink on ONE dish with no polariser or mechanical filters, but the transmitter is only 13.5km away on hill on other size of Shannon Estuary, about 100th of TX power and about 1000 times RX power, so the measly 450MHz separation works!
The Signal is actually DOCSIS shifted to Microwave, so receiver outdoor feeds a regular cable modem indoors. Due to the latency (152,000 km round trip for a "ping") Satellite two way data doesn't use regular TCP/IP, the modems at each end "spoof" or fake it.