small self-help transposer

pegasuspub

hi i am aware analogue is coming to a close,can any tech savy boards user advise on an old self help transposer consisting of off air channels 5,8,27,31 received at hill top (where there is no mains power) line fed through 220 meters of tx125 coax,the incoming channels are converted to 44,47,42,49 using alcad channel converters each feeding alcad zg401 single channel amps(i think the number is correct)there are two outputs from each amp and as the amps are linked together i have two dedicated outputs of 123db each feeding into 2 triax grids to give approx 75 degree spread into a valley with 7 houses,the system worked fine except for the odd hill fire and lightning strike.
the problem now is that two more houses want to use the system,these houses are almost at right angles to the other houses,i tried to add a third tx aerial but it seemed to be out of phase to the others and reduced channels 42 and 49,can anyone advise where i could get advise/technical info please?
also dtt signals (ch 21) are on the downlead at the tx site,as the tx and rx antennas are totally shielded by mountains what is likely to happen if i transmitted ch 21 with another alcad amp? i suppose the newer houses could wait for saor sat and the entire system wiil need upgrading later on,the newer houses have no interest in sky tv,and each of the 7 houses using the system pay the esb each year to a local farmer who supplies it to the tx site.sorry for the long message and thanks for any help.

watty

Google
Polytron in Bandon Co. Cork
Taylor Bros. In UK
There is a Trade supplier of CATV gear in Dublin, that's occasionally used even by RTE. I forget name. Sorry

12 element

http://www.mcgrathelectronics.ie

These are the Irish suppliers for Alcad. You mention the two outputs on the ZG401's are you talking about the bottom two F connectors? are they not looped across into the adjacent amp like in the picture.

watty

Actually I think it may have been McGrath I was thinking of. They have Dublin and Mayo offices.

You know your transposer has to close very soon, or else replace the aerials with coax.

There is also available now from Comreg long term 12.5GHz Terrestrial licences cheaply. Required to use Digital of course.

The Cush

watty wrote: »

You know your transposer has to close very soon, or else replace the aerials with coax.

There is also available now from Comreg long term 12.5GHz Terrestrial licences cheaply. Required to use Digital of course.

Are you referring to the deflectors that have shut down by the end of 2012?

Wasn't that legislation about the retransmission of the UK channels and not the Irish channels? I was under the impression the community-owned TV self-help schemes were assisted by RTÉ and legally provide the Irish channels.

I think it would be nightmare to cable somewhere like the Black Valley in Kerry.

pegasuspub

thanks for your help,the system was installed originally in 1994 (for the world cup i think) initially carrying rte1 and rte2 only on ch 44 and 47,rte technical were helpful but we could not meet their terms and conditions to get an official scheme(not enough houses and secure ,insured tx site if my memory is correct) later on tv3 and tg4 were added on channels 42 and 49.this is an extremly remote location and at the end of the valley is the atlantic ocean in fact most of this area cant receive sufficient tv3 signal,
thanks 12 element for your images that is the exact setup
the 4 amps are linked together with metal u links,this gives me 2 outputs ie, the top socket on the first amp and the bottom socket on the last amp looking at it from right to left,normally there is a 75 ohm termination into one of these sockets.however i was using two triax grid aerials to tx,one grid is plugged into the top output on the first amp (lhs)and the other grid is plugged into the bottom output on the end amp (rhs) there is 4 meters of tx125 coax between the amps and the grids.looking down the valley about 100 ft below the tx site there is a road thru the middle of the valley and the 7 houses are left and right off this road,this was why i used two grids,one to look at each line of houses.two more houses are now built at right angles to existing tx site so the two grids are not covering these 2.when i split one of the original grids to feed a third grid aimed at 2 new houses i get problems on both ch 42 and 49 with loss of power and range.system runs fine with 2 tx aerials only,it is not possible to drive upto the tx site even by tractor as it is on the side of a mountain and can only be reached carrying tools,meters,tv,aerials etc.possibly not the most technically advanced scheme but at the time it was the only way to get reception for the families involved at a very reasonable cost.once again thanks.

watty

The Cush wrote: »

I was under the impression the community-owned TV self-help schemes were assisted by RTÉ and legally provide the Irish channels.

Those will have to close end of 2012.

Three solutions:
1) Per home Saorsat, more expensive than DTT, but Government/RTE NL should subsidise massively. Same dish can do Freesat if done sensibly.
2) cheap pair of DTT mux fed by pair of ASI output sat receivers. Basically a Community DTT with full copy of Soarview. RTE NL will allocate a pair of suitable DTT channels. Maybe €15,000 to €30,000 but Government/RTE NL should subsidise massively. More suited to 100+ families as at less than this a free Saorsat install is cheaper (and can feed as many setboxes as you want)
3) 12GHz MMDS licence fed by pair of ASI output sat receivers. More expensive than (2) and LOS only.

I believe the Black Valley has Electric now since 1976. They should pay ESB to add fibre to the Electricity cable for Broadband as part of a National Fibre to Home/Cabinet scheme instead of Metro North.

The Cush

pegasuspub wrote: »

the system was installed originally in 1994 (for the world cup i think) initially carrying rte1 and rte2 only on ch 44 and 47,rte technical were helpful but we could not meet their terms and conditions to get an official scheme(not enough houses and secure ,insured tx site if my memory is correct) later on tv3 and tg4 were added on channels 42 and 49.this is an extremly remote location and at the end of the valley is the atlantic ocean in fact most of this area cant receive sufficient tv3 signal,

Thanks for that clarification pegasuspub.

12 element

If you could get a picture of the set up it would be great, but it sounds very difficult to access!
When you added the 3rd grid did you make sure all your cable lengths were equal after the split? What kind of splitters did you use?
I'm not too sure how this would work if you have two separate outputs maybe you'd have to add an other two grids to keep it symmetrical.

An other idea that might be worth looking into would be setting up satellite receivers for each channel you want and taking them in off soarsat and transmitting them out on your existing channels but this would limit you to the 4 channels you have unless you wanted to buy more equipment.

Sam Russell

Would not the OP be better to look at the aerials he is using? Surely the grids are too diectional for the new situation?

pegasuspub

thanks for you advice,as i said it is a remote area,it takes 30 minutes to walk/clamber up to the tx site although having seen the recent post of the tower climbers i think walking through furse and briars is easy.i have tried splitting the signal with a triax 2 way f type splitter,i also tried a small value catv tap,ive done my best to keep all coax lengths equal,at one stage i tried a triax stacking/phasing in reverse ie, one up lead with two equal length coax cables to the aerials,it must be possible to do this but im afraid i cant figure it out,maybe i should try 3 small yagi aerials,it may be best to wait for saorsat as a small antenna feeding multiple receivers in each house would be the best way to go,at this stage it is annoying me as i dont want to give up without getting a resolution or at least figure out what im doing wrong,all hadvice appreciated,thanks.

lucernarian

Here's a tip though it may be obvious. Those triax grids have a part of the back grid bent at an angle slightly over the dipoles. Generally it means that Grids have a wider acceptance angle when vertically polarised rather than horizontally polarised.

Also, what is stopping a DTT signal from simply being transposed (i.e. to hell with re-modulation and the likes), particularly if the S/N ratio was very good, e.g. above 40dB?

Sponge Bob

To_be_confirmed wrote: »

Also, what is stopping a DTT signal from simply being transposed (i.e. to hell with re-modulation and the likes), particularly if the S/N ratio was very good, e.g. above 40dB?

I'd like to hear that too, although the current 5,8,27,31 will go all UHF the outputs should continue to work. The OP should keep an eye on this list of DTT channels that Watty maintains.

Certain areas will be in satellite shadow even with Saorsat, if this valley has a mountain to the south it could be impossible to pick up SKY from the sun @ 11am position and the sun @ c.12.30pm position that Saorsat should appear in.

watty

There are various fancy problems with "transposing DTT". It's not at all robust for that. A system I was working on we had to switch to DVB-C (which is easier). DVB-S is easiest.

It can be done, but is expensive. This is why ALL the 51 RTE sites are fibre or microwave fed, no rebroadcast. AFAIK it's the same in UK. Nowadays if you can actually get ESB to a site, fibre is usually feasible. I'm told the plan is to have very few on terrestrial Microwave links. The old Analogue days RBL/RBS test to try and run Divis from Crystal Palace all by re-broacast at every stage was examined to DTT and abandoned as far too expensive. The BBC has done some research on the subject.

Before I tried it, I thought it would be easier than it was.

RTE NL will have to add some Community DTT Transmitters fed by Satellite.

Mike 1972

OP Id be very vary about spending large sums upgrading an analouge relay at this stage unless youre confident the gear can be used in the future for DTT signals.

The Cush wrote: »

Wasn't that legislation about the retransmission of the UK channels and not the Irish channels? I was under the impression the community-owned TV self-help schemes were assisted by RTÉ and legally provide the Irish channels.

There are(/were?) a small number of deflectors which carry/ied RTE and/or TV3 (in addition to the UK channels). Some by agreement with RTE (once licences were issued) others on their own initative.

Interesting that TV3 is carried on a "self help scheme" serving 7-9 houses but not on relays serving tens of thousands.

watty

Because TV3 won't pay.

The Cush

Question in the Dáil this week on the position of community television systems/deflectors when digital television becomes operational/post ASO.

Broadcasting Services

513. Deputy John O’Mahony asked the Minister for Communications, Energy and Natural Resources the position regarding community television systems when digital television becomes operational; and if he will make a statement on the matter. [38610/10]

Minister for Communications, Energy and Natural Resources (Deputy Eamon Ryan): The Commission for Communications Regulation (ComReg) is the statutory body responsible for the licensing of UHF Television Programme Retransmission services, as set out in the Wireless Telegraphy Act, 1926.

These community or ’deflector’ television systems retransmit the analogue signals of the UK and, in some cases, Irish ’free-to-air’ services and their future position in light of plans to switch-off analogue television broadcast transmissions by end-2012 is a matter for ComReg.

ComReg is an independent statutory body and as such I have no role in its day-to-day operations.

http://debates.oireachtas.ie/DDebate.aspx?F=DAL20101027.xml&Node=3325#N3325