Must the dish size be an educated guess ?

koansrc

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#1
I'm wondering, is it not possible to actually measure how much of a satellite signal is reaching a particular spot ? and so be able to actually calculate the dish size needed ? All these hot and cold spots seem to confuse the "official" footprint charts.

I'm thinking along the lines of : use an existing functioning dish & receiver, tune in to a chosen transponder and actually measure whatever little signal there is ( even though there may not be enough to actually watch anything ). Take the result and calculate the gain or signal increase that would be needed from the current setup.

Aren't "traces" of 2D signal (just as an example) detectable on a dish that is obviously too small for proper reception ?
 

Lancelot

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#2
A good idea BUT........
Receiver type and sensitivity, LNB type (and even batch), cable type and length and local oddities all make for a very hit and miss 'definitive' guide I would say.



L.:)
 

Likvid

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#3
Possible and feasible to do.

Just put up a large 5meter dish or something, bring a spectrum analyzer and print out the C/N levels, go home and make your work and calculate what the smallest dish you could get away with.

Plain easy G/T budget.
 

dxsat

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#4
It is possible to measure the signal strength being received at any point within the theoretical footprint of Astra 2D in europe, and to convert the signal strength into a dish size projection, via a mathematical formula.(which I don't have, unfortunately. I may be able to find it)
You are quite correct in assuming that a dish will receive traces of a 2D signal, which can be measured with a good meter, but are too weak to give a picture on a digibox. Most meters require a 'lock', and without this will show you nothing, as the signal is digital.
You would have to take the 'worst case' signal and base a projection from there. You would then have a number of options:
-Only one polarity received properly.
-Partial reception, loss of one or both polarities at some times of day.
-24 hour reception of both polarities.
-24/7 reception even in rain.

The last option might require an unfeasibly large dish in some areas.
Receiver sensitivity is generally within small variations for a given make and model. For example, it's known that Pace 2600 CI give good results on weak signals, with little variation from one 2600 receiver to another
The same applies to better LNB's. Invacom is the only make I can think of. There is almost no variation between batches of the the same model.
Cable length makes very little difference to signal quality, but cable type does. A good PF100 or similar will give good results regardless.
I don't think anyone has ever done a comprehensive, accurate map of dish size outside the official footprint. There have been a few published but they are generally inaccurate.
 

koansrc

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#5
snap said:
You are quite correct in assuming that a dish will receive traces of a 2D signal, which can be measured with a good meter, but are too weak to give a picture on a digibox. Most meters require a 'lock', and without this will show you nothing, as the signal is digital.
Are these meters common amongst professional installers ? Would I ever find one on ... Ebay ? Do they have a specific tech name ?
 

rolfw

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#6
Search for spectrum analyser, or satellite meter, the cheapest you will get for digital signals worth its salt is the Satlook NIT, from there they rise in price, my Swires Annie was over £1,600 and that is not one of the expensive ones. :)

Whatever you measure the signal with, your calculation is at best going to be an approximation, hence the number of threads regarding dish size and performance in the different areas.
 

dxsat

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#7
If it's any help, my Lacuna Mk3 meter will show a measureable 2D signal at a level a digibox cannot register. They cost about £300, but, as Rolf says, a spectrum analyser will do this job better but cost a fortune.

You could make an educated guess about how much bigger a dish needs to be to get a stable picture, when you're receiving a trace of 2D. The answer is usually a lot bigger.
I made the mistake of thinking that changing from a 1.2 metre dish to a 1.5 metre would pull in horizontal 2D channels at night, 6 pm - midnight. It didn't, and I had to spend yet more money on a 1.8 metre.
 

iceman

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#8
snap said:
If it's any help, my Lacuna Mk3 meter will show a measureable 2D signal at a level a digibox cannot register. They cost about £300, but, as Rolf says, a spectrum analyser will do this job better but cost a fortune..
I would like to add that a good quality spectrum analyser will also show signals not detected by inferior sat meters...
For example,2D vertical transponders in Cyprus not visible to a receiver or sat meter will show up on the spectrum analyser..
 

izefisherman

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#9
iceman said:
For example,2D vertical transponders in Cyprus not visible to a receiver or sat meter will show up on the spectrum analyser..
Exactly, thus giving a rough indication on how much one would need to increase dish size to actually receive it by comparing the spectrum to a just about receivable signal.
 

Llew

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#10
Even my old Metrix analogue spectrum analyser will give a good display of otherwise barely readable digital signals on my STBs, and that's ancient by modern standards.

Llew
 

koansrc

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#11
So, perhaps those with meters and analyzers, new or old, could post some results comparing eg. 3 frequencies. The BBC1 on 2D, the Euronews freq and the SKY News freq, as a typical weak signal, a difficult signal and an easy freq respectively. Obviously all factors of each particular setup would affect the absolute readings BUT not the relation between them. So perhaps we will find that the BBC1 signal is 45% weaker than the Euronews signal which is 28% weaker than the SKY News signal in Cyprus, where as in Spain the numbers are different (or will they ?). Does this make any sense ? Anyone care to go first ?
 

Analoguesat

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#12
The exercise would be totally futile. Signal strengths from any particular satellite will vary greatly over a few miles in extreme fringe areas due to minute imperfections in the transmission reflector surface.

Results in one town would be comparable but could be useless 20 miles down the road. Theres plenty of evidence for this in southern Spain where received signal strength vary wildly over a dozen miles or so. The info is in the archives here somewhere - about 18 months back.
 
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