Is your DStv satellite dish too small?

That "slightly" higher signal level you refer to, is arround 3dBW. 3dBW translates to double the power, not slightly as the number seems to mislead (see basic logaritmic calculations).

Therefore a receiver located at a point 3dBW lower than the "sweet spot" will have to have twice the area to achieve the same signal gain.

It is interesting to note that a 90cm dish has roughly 2.2 times the area of a 60cm dish while a 80cm dish only comes in at about 1.7 times. This would somehow suggest that Multichoice is ensuring good reception for the worst case scenario (which makes sense).
 
Since upgrading to HD in December there have been a number of times when my HD signal went out, but the SD signal on my extra-view decoder was fine, coming from the same dish. It's very annoying because they don't tell you this when you fork over the cash for the HD decoder.
 
Maybe somebody can clear this up for me as I don't understand it...

We changing signal or whatever in order to get mor HD channels and therefore need a bigger dish.

How come SkyDigital in the UK has a minuscule dish (it's seriously small!!!) and they have like 50 HD channels???? And I've never ever experiencd any signal degradation over there and trust me, when it rains, it rains!!

Sounds like a money making scheme to me from Multichoice
 
Pixual said:
Since upgrading to HD in December there have been a number of times when my HD signal went out, but the SD signal on my extra-view decoder was fine, coming from the same dish. It's very annoying because they don't tell you this when you fork over the cash for the HD decoder.
Click to expand...

The switch to DVB-S2 for HD has not happened yet... Something else is wrong on your setup.
 
IceDreama said:
Maybe somebody can clear this up for me as I don't understand it...

We changing signal or whatever in order to get mor HD channels and therefore need a bigger dish.

How come SkyDigital in the UK has a minuscule dish (it's seriously small!!!) and they have like 50 HD channels???? And I've never ever experiencd any signal degradation over there and trust me, when it rains, it rains!!

Sounds like a money making scheme to me from Multichoice
Click to expand...

The satellite footprints are much smaller in Europe, so the signal is a lot stronger when it arrives at the dish.
 
IceDreama said:
Maybe somebody can clear this up for me as I don't understand it...

We changing signal or whatever in order to get mor HD channels and therefore need a bigger dish.

How come SkyDigital in the UK has a minuscule dish (it's seriously small!!!) and they have like 50 HD channels???? And I've never ever experiencd any signal degradation over there and trust me, when it rains, it rains!!

Sounds like a money making scheme to me from Multichoice
Click to expand...


The satellite that Multichoice transmits through is far away - it is sitting in a geostationary orbit directly above Indonesia (Northern Australia), but has it's antennas pointing our way to cover the whole continent of Africa.

I would imagine the UK sat is not as far away, and uses a more concentrated beamwidth on its antenna to only cover the UK - a WAY smaller footprint compared to the whole of Africa, right ? We therefore need more gain at the dish (bigger dish) to reach our far more distant sat, which has a wider angle of radiation, and a comparably weaker signal due to the distance.

Why do we not use a sat in a geostationary orbit closer to us ? Firstly it will then only cover a very small part of our continent and exclude millions, and secondly the geostationary belt above the earth is very narrow. A sat needs to be exactly on this belt in order to remain in the same position in the sky every day. If it is off this belt, the sat will appear to move around and never sit still. This would never work with your dish as it is focused on one spot in the sky. Having a parking bay in this belt is therefore PRIME real estate, and is quite full of sats already. The sat that they are using at the moment, was the best compromise they had in terms of large footprint to cover the entire continent of Africa
 
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T3rminator said:
That "slightly" higher signal level you refer to, is arround 3dBW. 3dBW translates to double the power, not slightly as the number seems to mislead (see basic logaritmic calculations).

Therefore a receiver located at a point 3dBW lower than the "sweet spot" will have to have twice the area to achieve the same signal gain.

It is interesting to note that a 90cm dish has roughly 2.2 times the area of a 60cm dish while a 80cm dish only comes in at about 1.7 times. This would somehow suggest that Multichoice is ensuring good reception for the worst case scenario (which makes sense).
Click to expand...

Quoted for emphasis. Good spot, T3rminator.
 
Since canceling my DStv last year my dish is 100% too big. Should probably take it down.
 
Logarithmic scale

The graphic below from Intelsat shows that central SA enjoys slightly higher signal strength than the rest of the country.
Click to expand...

This "slight" variation in signal strength is 2dB.
This means a change in signal of 10^0.2=1.58
i.e. the signal within the 55dB contour is 1.58 times the strength of the signal in the 53dB contour.
 
Pity that mono-choice does not have a proper flexivle online streaming platform. 3mbps is enough for 720p HD streaming. But until they (or hopefully another company) comes up with a solution I'll be anchoring in TPB.
 
T3rminator said:
That "slightly" higher signal level you refer to, is arround 3dBW. 3dBW translates to double the power, not slightly as the number seems to mislead (see basic logaritmic calculations).
Click to expand...

True, but in the RF world 3 dB is considered little. When planning PtP microwave links, a fade margin of about 10 dB is fairly common.
 
Tacet said:
True, but in the RF world 3 dB is considered little. When planning PtP microwave links, a fade margin of about 10 dB is fairly common.
Click to expand...

Yikes. If my memory isn't failing me now, we used to design filters (in digital signal processing / linear systems) using -3dB as the cutoff. That is, anything beyond that cutoff is expected to have such poor SNR that it is considered "filtered".
 
All the satellites are 40k km from the earth, or they would not appear to maintain the same position relative to a viewer on the ground

Most of the transponders that serve South Africa have a much broader footprint than those in use over Europe. Given that a transponder serving Southern Africa must cover an area of 10000 sq km with the same radiated power of a transponder serving South East England, the surface area is maybe 3000 sq km, the effective power available to the LNB is 30 times in the UK compared with here. Therefore a 40cm dish is quite adequate

If you have a HD-PVR, a correctly aligned 90cm dish will give drop outs caused by weather 100 times less often than a 60cm dish

Also, go for an alu-zinc dish, not painted mild steel. In the Cape, I have seen 9 month old steel dishes going rusty
 
A MultiChoice accredited installer installed my HD-PVR system using a 60CM dish. After the installation I also got a call from MC surveying my satisfaction with the service, in which I mentioned that I was concerns that the 60CM dish might be too small. I was assured that it was not and, to date, have not had issues with receptione etc. My SD-Decoder also loses signal long before the HD-PVR does during bad weather as well.

In any case, the fact that MC now comes back and says most dishes installed for HD telly and DVB-S2 are now actually too small is their faux-pax, not the accredited installers or customer's
 
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Jan said:
Yikes. If my memory isn't failing me now, we used to design filters (in digital signal processing / linear systems) using -3dB as the cutoff. That is, anything beyond that cutoff is expected to have such poor SNR that it is considered "filtered".
Click to expand...

Yep, but that's for circuitry on a board. MW transmission is a different game entirely - a typical system will be able to transmit up to about 20 dBm, with a receive sensitivity of about -70 dBm. That is a 90 dB difference...

Just a note - quoted numbers are for a PtP system I'm currently working with.
 
I don't believe a thing MC says.
LNB Technology has improved so much, I use a smaller dish and by taking the time to adjust the stupid thing properly I hardly ever lose signal. Anyway I've cancelled DSTV, too much junk and nothing to watch at all.

MC need more money so this is a ploy to get their subs to replace dishes and keep their "accredited installers" in business, I bet a lot of people have started to install their dishes themselves. What would you expect from a media conglomerate, certainly not the truth.
 
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