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UK TV - signal disappeared?


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We are in Bearn, 64, and installed a 1200mm dish late last summer and enjoyed good reception during our visit in October. Returning for the first time at the beginning of March, the reception of all free to air channels was again good. The signal did, however, disappear over a 10-15 minute period every night at around 10.30-10.45 (French time), which at that time of night was just an inconvenience.

Just before Easter the signal started to disappear earlier until at the beginning of last week, before we left, there was none at all.

It may be that the dish has moved slightly although it is in a well protected but accessible position, and needs adjusting, or is it a further 'refinement' of the satellite signal transmission?

Has anyone else encountered a similar problem? Advice appreciated.
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Thanks for your suggestion re a 'man with a machine'. This had occurred to us but we were unsure whether the transmission had been moved again.

Last year we tried to get a quote from the local Pro & Cie shop but they declined, saying that UK TV reception was no longer possible. Hence we did it ourselves, successfully until the signal disappearance a week or so ago. We will be back later this month and will try with another shop if the signal hasn't moved.

Thanks again for your reply.
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The one slightly counter-intuitive thing about satellite dishes is that the larger you go, the narrower the beam (the more tightly focused) it is reflecting to the LNB, and therefore the more critical the exact positioning becomes.

The upside is the greater gain, the downsides are the lowered ability to compromise between the slightly different positions of the various satellites which are all nominally sitting at 28.2E, but each in their own 1km cube box.

The other downside (which I'll bet is more applicable to your site) is the bigger the dish: the greater the suseptibility to being blown off-station by the wind.  

The only way I can get my 1.2m dish into an acceptable position is to drag a tv and a receiver to the dish and keep scanning after each move (I have a receiver which gives a signal strength for each of the frequencies as it's tuning up the band).

Then we get another bloody gale, and it's back to square one!

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[quote user="Jonzjob"]Which end did he tweek HSD?? [6]

Nearly forgot to give a reminder about the BIG change to French TNT transmissions tomorrow.

Full HD transmissions are starting tomorrow. If you don't know then just google it..

[/quote]

...and after all the bally-hoo FR3 (Limousin) still looks like it's broadcasting through a net curtain!

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That's presumably the terrestrial TNT (as opposed to sat?) or the sat regional version...?

Apparently the problem is that in order to allow for the regional opt outs most regions have to pass the Paris France 3 HD signal through their studios, and thence on to the transmitters so if any part of the chain isn't HD capable then neither is the end picture off the transmitter (I'm putting it simply because I don't know exactly the pathways).

If you watch the France 3 HD national signal on Fransat or TNTsat it's pretty good. TNTsat actually manage to get our boxes to opt in and out of the regional decrochages, that's to say they hop frequency to the local version just before the opt out and hop back to the national HD version just after; on our box there's a few seconds of blank screen at each change. On Fransat you can watch the National France 3 HD version on channel 300, but of course you won't get the decrochages.

One way round would be for the engineers to do a similar opt in and out at the transmitters (ie switch to the studio for the local decrochage and back to the sat distribution for the rest of the time). But that would involve a whole lot of extra equipment, and the problem will in any case go away by 2017 when we're promised that France 3 regionals will have gone all HD anyway, so the pass through on the way to the txs will be HD.

But you're right, there's been disappointment nationally that France 3 on terrestrial still looks awful in most areas apart from Paris.
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I should have added - for GP's benefit as he knows what he's on about (and may know this already) - that you don't need a Fransat receiver to access France 3 HD on 5 deg W - it's replaced the FTA SD version on 11591 MHz and is also FTA.

So those of us who find the likes of Julie Andrieu and Carole Gaessler irresistible can now enjoy them in wonderful FTA HD.
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Just a quick question on French TV reception?

When you can recieve all the channels with an ordinary, old fashioned TV ariel what is the point of a sat dish? This is a genuine question. We have an ordinary ariel and get all the channels clear as a bell.

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If you can receive all the channels with an ordinary old fashioned TV ariel there is not much point in using a sat dish.**

The purpose of TNT channels by satellite is precisely for those that cannot receive a signal via a rooftop aerial as they can't get a direct line of sight to the transmitter. Think mountains etc.

Danny

**Unless one does not have an aerial on the roof and already has a sat dish and maybe also wants the extra channels available by satellite.

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As Danny says.

France built over 3500 UHF main stations and relays in the period 1964 - late 1990s. Pratically every nook and cranny had one, sometimes only serving a few houses (cf Britain where the criterion was eventually 500 homes unserved before a relay could be considered, we have 1150 stations approx).

Come digital switch-over it was simply impractical to maintain such a large network, so in fact only about 1600 relays carry French digital TV, the rest lie sadly silent. In some favourable cases people thus deprived can make use of a main station, but it's reckoned that UHF coverage dropped from over 99% of homes to about 95%.

France already had an analogue satellite distribution system in place, which was already used by about 2 million homes, mostly to pick up France 5/Arte/M6 which had incomplete terrestrial coverage. This sat distribution was ideal for conversion to digital and meant that those with dodgy or lost terrestrial after switchover had a simple solution for maintaining their pictures. Another operator (Canalsat effectively) provided yet another sat alternative via TNTsat.

Where we are in 24 our terrestrial signals aren't brilliant unless you're up on a hill, but satellite romps in, and we know a number of people who - having seen their rateau crash onto their roofs during the 1999 hurricane - swore never to replace them having discovered just how convenient satellite is.....

In our case it means we can cart the sat receivers back to Britain and go on watching French TV.

But - indeed - if a rateau works (which in 95% of cases it will) then it's convenient, and the receivers are FAR cheaper.

Incidentally, a lot of French TV is now available via FTA satellite across 19 E 5 W and 9 E. TF1/2/3/4/M6/Arte/W9/TMC/LCP/BFM/iTele/LCI/TV5 are all FTA so if like me you have satellite dishes pointing in all directions the need for Fransat and TNTsat has largely disappeared.

You didn't really need to know all that did you.....!
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  • 1 month later...
We live in 65 near Madiran, and even on a 1.2m dish the reception now varies a lot - more or less OK on a modern Humax decoder but even that is weather dependent. Compared to a year ago, when we never had any problems, the signal now seems to be weaker.

There is one issue which I fail to understand, the difficulty of aligning a larger dish. Using an elementary calculation, the resolving power of an optical element can be calculated from the ratio wavelength being received divided by the aperture. This gives an angle, in radians, from which you can calculate the minimum distance apart of two objects which can just be resolved, known as the Rayleigh criterion.

Carrying out this calculation for a 1.2 metre dish receiving a 10GHz signal, ie 3cm wavelength, the minimum angle comes to 1/400. Since the satellite is about 40,000 kms away, this means that the minimum distance apart for two objects at that distance to be resolved is 100kms. There is no way that the individual Astra 2 satellites, which are only a few kms apart, can be resolved by a dish of that size, so the dish will "see" all of them.

What am I missing? In general I have found aligning my dish no more difficult than my original smaller one, although it has to be precise within 1/400 radians, ie about 1/7th of a degree -  difficult enough!

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[quote user="Buzby"]We live in 65 near Madiran, and even on a 1.2m dish the reception now varies a lot - more or less OK on a modern Humax decoder but even that is weather dependent. Compared to a year ago, when we never had any problems, the signal now seems to be weaker.

There is one issue which I fail to understand, the difficulty of aligning a larger dish. Using an elementary calculation, the resolving power of an optical element can be calculated from the ratio wavelength being received divided by the aperture. This gives an angle, in radians, from which you can calculate the minimum distance apart of two objects which can just be resolved, known as the Rayleigh criterion.

Carrying out this calculation for a 1.2 metre dish receiving a 10GHz signal, ie 3cm wavelength, the minimum angle comes to 1/400. Since the satellite is about 40,000 kms away, this means that the minimum distance apart for two objects at that distance to be resolved is 100kms. There is no way that the individual Astra 2 satellites, which are only a few kms apart, can be resolved by a dish of that size, so the dish will "see" all of them.

What am I missing? In general I have found aligning my dish no more difficult than my original smaller one, although it has to be precise within 1/400 radians, ie about 1/7th of a degree -  difficult enough!

[/quote]

Would the same be true of - say - a 90cm dish? If so it would seem to fly in the face of experience whereby it is possible to 'favour' one sat over another (in the same nominal location) where the transponder beams - and therefore the relative received signal strengths - may differ. (Classic FM comes to mind).

Certainly the ordinary physical business of moving a dish about to find the damned sats is harder the bigger and heavier the dish is - perhaps that's what effects my view of ease of station finding/keeping?

I never cease to be amazed at how rudimentary the alignment and attachment fittings remain on even quite high-end products: having struggled for hours to get the best possible signal strength, the effect of tightening the bolts then throws the dish half a degree off-station!

The most intelligent design for dish alignment I've seen is for my satellite internet which has a bleeper whose pitch alters the nearer you get to peak signal, and to actually make the adjustments you turn a geared bolt. Easy, smooth and accurate. Would that all systems were like that!   

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I am afraid my calculations are wrong! It seems I am unable to divide 1.2m by 3 cm, so the ratio should be 40, not 400.

This makes things even worse for resolution, but I think you've hit the nail on the head, in that the adjustments provided are totally inadequate for the precision required. A smaller dish will have a wider range of acceptance, but the signal for the narrow beam transmissions on a "small" dish will be too weak for the decoder. As a result the whole process becomes hit or miss.

As you have found, a peak signal meter will certainly help, but now it seems even a 1.2m dish is barely adequate.

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There is an easier way to make this calculation.

A 1.2 meter dish has an aperture of 1.5 degrees, that is the -3dB point. As the aperture works both ways (left and right) we need half the aperture for the calculation, 1.5/2=0.75

The current positions of the Astra2 fleet is:

Astra 2E: 28.52 degrees east

Astra 2F: 28.20 degrees east

Astra 2G: 29.19 degrees east

The Astra2E satellite has been placed quite far from the original 28.2 position, probably to occupy the former Eutelsat slot at 28.5 degrees.

The difference between Astra2F and Astra2E is 0.32 degrees. So when you point your 1.2 meter dish at Astra2F at 28.20 degrees the signal for Astra 2E will be 0.32/0.75*3=1.28 dB lower.

That is not much, but it might be enough to notice.

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