Question about TV aerials (Bill Wright?)

[williamwright]

Thirty years ago Sxxx came out with some tellys that needed masthead amps even in medium signal areas.

Bill

[williamwright]

Just answer my question: "Why do you believe that an amplifier can correct signal loss caused by sharing the signal between several outlets but it can't correct signal loss caused by cable length?"

Regarding your statement: "Modern sets have such sensitive receivers that the problem is more with their ability to pick up remote transmitters in a sidelobe instead of the wanted stations in the direct beam" why would increased receiver sensitivity make that more of a problem? Two possible meanings of what you say:

1. You mean that the remote signals would be co-channel with the local ones so would cause interference. But the receiver sensitivity would have no effect on the signal/noise ratio.
2. You mean that the set would tune to incorrect transmissions. Most sets allow regional selection. Otherwise it's down to the installation. It isn't reasonable to blame better sensitivity for this 'problem'.

Incidentally, modern sets are not 'more sensitive'. They have better decoders, and front ends with lower thermal noise and better protection against out-of-band signals.

Bill

[williamwright]

A Gp A on those channels will have zero gain over a bit of wire.

Bill

[charles]

prior to that they had a model that would overload with 12 uhf channels spread across the band. You couldn't get noise free signals on any chaannel.

[Martin Brown]

It can provided that the mast head amplifier isn't swamped by other strong local RF interference. Mast head amplifiers of old almost invariably have too much gain for their own good. A sharing amplifier is also much more modest gain and acting more like a low gain buffer.

#2. Particularly in Manchester after digital day the Welsh channels in the sidelobe of an antenna pointed at Winter Hill were strong enough and found first to become the defaults on some older Panasonic sets.

You had to unplug the coax while it scanned past the low end.

The UHF front end is much more sensitive and lower noise now than any tuner circuit that would have ever been on a classical analogue set.

[williamwright]

I built a system for Reuters when they moved into 200 Grays Inn Road that had every channel occupied from 40MHz to 860. Then they moved in with an assortment of tellys...

Years later my systems in prisons that had a lot of channels revealed that some of the very cheap LG 14" sets coped better than the more expensive makes in the staff offices.

Bill

[williamwright]

Well yes, but it's down the the installer to check the spectrum.

Mast head amplifiers of old almost

They often still do, because ignorant installers and DIYers think 'the more gain the better'. Nowadays most MHAs have variable gain. When that idea came out some had a variable attenuator on the input! Nowadays it's usually interstage. Still not as good as using a single stage amp of course.

You'd be surprised. Most don't use efficient splitting. A typical example currently on sale has gain of about 26dB feeding a stripline thing, sort of like a printed directional tap-off unit, to feed each output. The loss is 15dB to each port, then most of the power is dumped in a terminating resistor!

Yes, this was a notorious problem. We had the same here. Most of S Yorks has strong Belmont and Bilsdale, and some areas have Crosspool, all were Gp A, so to tune Emley you had to pull the aerial out for the first half of the scan. Some sets insisted on autoscanning in the night and I was selling a lot of in-line Gp B filters (which sometimes killed Channel 5 on 37.)

Bill

[Andy Burns]

How long will CH55 be around for? 700MHz auction taking place in March?

[Mark Carver]

It's on Death Row, Ofcom licence expires next June. Arqiva can pull it at very short notice before then (as they did with COM 8) BTW COM 8 licence is still active, also until 30/6/22, not that Arqiva will ever bring it back

[Andrew]

So where will BBC4 HD, News HD etc go ?. Presumably at some point most people will (or should/could) be watching BBC1,2, ITV, C4 and C5 in HD, making Freeview 1,2,3,4,5 redundant ?

[Peter Able]

Thanks for that, both. I'd no idea - but have tried to bone up and, is this right?

All of the re-works have to happen simultaneously for things not to go wrong?

Using a full HD TV, we'll still get the current quality and quantity of service?

It'll offer, to Crystal Palace users with a group A aerial, the benefit of stuff moving from C55 to lower channel numbers?

What's to go wrong ;)

PA

[S]

well from my crystal ball, I expect some of the following:

the conversion of DVB-T muxes to DVB-T2 (that being PSB1, PSB2 ARQ A, ARB B and SDN. (PSB3 is already T2)

De-duplication of the DVB-T converted to DVB-T2 public service channels on PSB 1 & PSB 2 muxes vs the public service DVB-T2 channels on PSB3 mux

Both of the above will increase mux data capacity to allow some Mux 7 channels to move to the remaining muxes.

WILDCARD No 1.

The ARQ A, ARQ B and SDN are made into 3 national SFN's (having proven the concept of a SFN for Mux 7 and 8 on ch's 55 and 56 over the past few years)

That could produce a new 600 MHz clearance for 5G or create opprtunities for new Muxes (For the latter, OINK OINK, oh look, theres a jumbo jet of pigs flying by! :-) )

WILDCARD No 2.

Teh national DTT/Freeview transmitter network gets closed down and viewers moved to online streaming services (and even Freesat gets closed too!

[Peter Able]

Thanks. I boned up on some of that by reading

where they suggest your "some Mux 7 channels" will be six - somewhat less than COM7 currently carries.

As for wildcard 2, after it has crashed and burned, will someone say "Hey, let's build a new network based upon super-high-power wireless beaming simultaneously to every home in the land!"

PA

[Andy Burns]

Are you buying salt in bulk?

[Mark Carver]

Short term, they will probably cease on Freeview. Medium term, they should re appear whenever the conversion of the remaining 6 muxes to DVB-T2 starts, and flags the end of SD/HD dual emission

[Mark Carver]

Once COM 7 on Ch 55 does close, that's it, nowhere in the UK will anything above UHF Ch 48 be used for TV broadcasts ever again, so don't go to too much expense to receive Ch 55 for what will only be a maximum of 17 more months.

There is no 'roadmap' for the conversion of the remaining five DVB-T1 muxes  to T2, the government seem to be preoccupied on other matters at present !

[S]

Has any one noticed patterns appearing on the national TV transmitters?

It seems that SDN, ARQ A and ARQ B are often found on chs 22, 25 and 28 or on 29, 31 & 37?

and that PSBs 1, 2, 3 are often found on chs 41, 44 & 47....

Thats what led me to think of a national SFN for SDN, ARQ A and ARQ B is partially in the making......

[Mark Carver]

The main 6 muxes are jammed packed with services, and with robust FEC measures, that makes any large scale SFN working impossible. The geographical limit for the path difference on two receivable transmitters is about 20 miles

COM 7 is a national SFN, but with fewer services, and weaker FEC, so its limit is about 70 miles (DAB radio has a similar figure)

In order to make the main 6 muxes national  SFNs, you'd have to reduce the number of services (or each service's bit rate), so it's largely self-defeating

[Peter Able]

Well, I do - by the palette, actually...;)

I'm missing something !

PA

[Peter Able]

Well, with the HP Spectrum Analyser the only effort was getting the analyser up and down a loft ladder. I'd already installed a string crib for the aerial, so moving it in three dimensions was no problem.

Except for all outputs of the distribution amp outputs being

50Hz-modulated. Unbelievable! The Labgear dist amp starts with a 24vAC transformer, a bridge rectifier and then a 25v electrolytic - which was well bulging! With that replaced by a 40v cap, C55 was no problem.

I've not been able to find a cct diag for the Labgear, so can't decide if it was a batch build problem or an original design fault.

Afterall, 24v supply - 25v smoothing cap - what could go wrong?

PA