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Are sat dishes too small?
I ask this as some people I know who live here darn souf, seem to always get
duff reception when the cloud cover is bad. OK I don't know enough about the location etc to comment, but there do seem to be a lot of people in forums etc complaining recently, and i just wondered if in order to make the dishes look smaller the gain has been paired to the bare minimum. Brian -- -- From the sofa of Brian Gaff - Blind user, so no pictures please! |
Are sat dishes too small?
"Brian Gaff" wrote in message ... I ask this as some people I know who live here darn souf, seem to always get duff reception when the cloud cover is bad. OK I don't know enough about the location etc to comment, but there do seem to be a lot of people in forums etc complaining recently, and i just wondered if in order to make the dishes look smaller the gain has been paired to the bare minimum. The belt and braces wearers amongst us install the next size up just in case. No idea of any recent problems though - wasn't watching it yesterday. -- No plan survives contact with the enemy. [Not even bunny] Helmuth von Moltke the Elder (\__/) (='.'=) (")_(") |
Are sat dishes too small?
Brian Gaff wrote:
I ask this as some people I know who live here darn souf, seem to always get duff reception when the cloud cover is bad. OK I don't know enough about the location etc to comment, but there do seem to be a lot of people in forums etc complaining recently, and i just wondered if in order to make the dishes look smaller the gain has been paired to the bare minimum. I think a better question would be: do satellite operators try to get too many channels into each transponder? DSB dish sizes tend to be set by planning law. They are set based on what is permissible without explicit planning permission. (I'm not sure how this works in Scotland, where you need bigger dishes. It might be they have larger limits or it might be there is some element of cosmetic sizing down South.) The satellite operators are constrained by the power from the photo cells on the satellites, but choose the technical parameters of their signals so as to get the maximum revenue (i.e. sell as many channels as possible) consistent with producing an acceptable signal most of the time. Increasing the bit rate on a multiplex means a higher signal to noise ratio is required to receive it accurately. The system is designed for "most of the time", so heavy cloud may well break it. Incidentally, they actually increase the uplink power if the uplink is affected in this way. I'd suggest that if bigger dishes became common, they would take advantage of them until the availability was reduced to the current level. One other variable is that the people with problems may be those with their dishes least accurately aligned, or maybe even with warm objects in the field of view. Brian |
Are sat dishes too small?
David Woolley wrote:
Brian Gaff wrote: I ask this as some people I know who live here darn souf, seem to always get duff reception when the cloud cover is bad. I think a better question would be: do satellite operators try to get too many channels into each transponder? squeezing in extra channels would increase artefacts, rather than reduce signal level or quality. DSB dish sizes tend to be set by planning law. They are set based on what is permissible without explicit planning permission. Sky zone1 elliptical dishes are considerably smaller than the 1m dishes usually allowed without planning permission. |
Are sat dishes too small?
On 05/06/2012 08:53, Brian Gaff wrote:
I ask this as some people I know who live here darn souf, seem to always get duff reception when the cloud cover is bad. OK I don't know enough about the location etc to comment, but there do seem to be a lot of people in forums etc complaining recently, and i just wondered if in order to make the dishes look smaller the gain has been paired to the bare minimum. Brian Did you mean to ask "Are Sky dishes too small?" I have always understood that the 45 cm Sky disk was the minimum size that Sky could get away with for (usually?) reliable reception. When I looked into getting Freesat a couple of years - or maybe more - ago, the minimum size of disk available relatively cheaply, complete with receiver, was 65 cm. Apart from having to move the dish because of a tree growing too high, I've never had reception problems from 28.5° here in Sussex, no matter what the cloud cover. What is the reception like much further north, particularly in Scotland? -- Jeff |
Are sat dishes too small?
In article , Jeff Layman
scribeth thus On 05/06/2012 08:53, Brian Gaff wrote: I ask this as some people I know who live here darn souf, seem to always get duff reception when the cloud cover is bad. OK I don't know enough about the location etc to comment, but there do seem to be a lot of people in forums etc complaining recently, and i just wondered if in order to make the dishes look smaller the gain has been paired to the bare minimum. Brian Did you mean to ask "Are Sky dishes too small?" I have always understood that the 45 cm Sky disk was the minimum size that Sky could get away with for (usually?) reliable reception. When I looked into getting Freesat a couple of years - or maybe more - ago, the minimum size of disk available relatively cheaply, complete with receiver, was 65 cm. Apart from having to move the dish because of a tree growing too high, I've never had reception problems from 28.5° here in Sussex, no matter what the cloud cover. What is the reception like much further north, particularly in Scotland? ISTR that Sky kept the size of the dish small so as to prevent them being used for any competing satellite service. Don't know if thats strictly true;!. Course a lot of them are poorly aligned and they have low "ish" gain anyway so no surprise when they fall over in bad weather;!... -- Tony Sayer |
Are sat dishes too small?
In message , Brian Gaff
wrote I ask this as some people I know who live here darn souf, seem to always get duff reception when the cloud cover is bad. OK I don't know enough about the location etc to comment, but there do seem to be a lot of people in forums etc complaining recently, and i just wondered if in order to make the dishes look smaller the gain has been paired to the bare minimum. Brian Or is it just poor installation? I have fitted a zone 2 mini-dish in an area where 99.9% of installations are a zone 1 dish. Previously I had a zone 1 dish and the only time I lost signal was when it was raining so hard the road outside my house became a 6 inch deep river for a short period. -- Alan news2009 {at} admac {dot} myzen {dot} co {dot} uk |
Are sat dishes too small?
"Brian Gaff" wrote in message
... I ask this as some people I know who live here darn souf, seem to always get duff reception when the cloud cover is bad. OK I don't know enough about the location etc to comment, but there do seem to be a lot of people in forums etc complaining recently, and i just wondered if in order to make the dishes look smaller the gain has been paired to the bare minimum. Brian -- -- From the sofa of Brian Gaff - Blind user, so no pictures please! Most people who, like myself, spend much of their time living on a canal boat use a 12" dish because it's beam width is slightly greater and so the signal doesn't keep being interrupted when the boat moves slightly. There isn't ever a problem with signal strength (unless we're moored behind a tree!) -- Allan Jones - N/B 'Keeping Up' www.keeping-up.co.uk |
Are sat dishes too small?
Andy Burns wrote:
David Woolley wrote: Brian Gaff wrote: I ask this as some people I know who live here darn souf, seem to always get duff reception when the cloud cover is bad. I think a better question would be: do satellite operators try to get too many channels into each transponder? squeezing in extra channels would increase artefacts, rather than reduce signal level or quality. Obviously once you have chosen the low level coding and aggregate bit rate, you can only increase the number of channels by reducing the bit rate per channel. However I'm talking about the process that would have gone into deciding the coding and bit rate. Whilst there would be a quality multiplier in determining the actual number of channels, a higher aggregate bit rate always allows more channels for a given quality, and they would have chosen the highest bit rate that they could get away with, subject to available technology and the link budget on the majority of days. |
Are sat dishes too small?
David Woolley wrote:
I'm talking about the process that would have gone into deciding the coding and bit rate. Whilst there would be a quality multiplier in determining the actual number of channels, a higher aggregate bit rate always allows more channels for a given quality, and they would have chosen the highest bit rate that they could get away with, subject to available technology and the link budget on the majority of days. True. Does the symbol rate, QAM and FEC setting vary purely based on which satellite and beam a transponder is on, or based on more commercial considerations? I presume Astra/Eutelsat set the parameters unless someone is renting an entire transponder? |
Are sat dishes too small?
On 05/06/2012 8:53 AM, Brian Gaff wrote:
I ask this as some people I know who live here darn souf, seem to always get duff reception when the cloud cover is bad. OK I don't know enough about the location etc to comment, but there do seem to be a lot of people in forums etc complaining recently, and i just wondered if in order to make the dishes look smaller the gain has been paired to the bare minimum. Brian their dishes are the right size - assuming they are pointing in the correct direction. -- Gareth. That fly.... Is your magic wand. |
Are sat dishes too small?
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Are sat dishes too small?
On Tue, 05 Jun 2012 10:07:55 +0100, Jeff Layman wrote:
On 05/06/2012 08:53, Brian Gaff wrote: I ask this as some people I know who live here darn souf, seem to always get duff reception when the cloud cover is bad. OK I don't know enough about the location etc to comment, but there do seem to be a lot of people in forums etc complaining recently, and i just wondered if in order to make the dishes look smaller the gain has been paired to the bare minimum. Brian Did you mean to ask "Are Sky dishes too small?" I have always understood that the 45 cm Sky disk was the minimum size that Sky could get away with for (usually?) reliable reception. When I looked into getting Freesat a couple of years - or maybe more - ago, the minimum size of disk available relatively cheaply, complete with receiver, was 65 cm. Apart from having to move the dish because of a tree growing too high, I've never had reception problems from 28.5° here in Sussex, no matter what the cloud cover. I went for 65cm, just to be on the safe size. What is the reception like much further north, particularly in Scotland? That needs Skye dishes. -- Peter. The gods will stay away whilst religions hold sway |
Are sat dishes too small?
One thing that did intrigue me was that some sats vertical and horizontal
signals are not exactly that and need a bit of skew added, somone here suggested the dishes were small to make them useless for other sats, but maybe the skew does that. Brian -- -- From the sofa of Brian Gaff - Blind user, so no pictures please! "the dog from that film you saw" wrote in message ... On 05/06/2012 8:53 AM, Brian Gaff wrote: I ask this as some people I know who live here darn souf, seem to always get duff reception when the cloud cover is bad. OK I don't know enough about the location etc to comment, but there do seem to be a lot of people in forums etc complaining recently, and i just wondered if in order to make the dishes look smaller the gain has been paired to the bare minimum. Brian their dishes are the right size - assuming they are pointing in the correct direction. -- Gareth. That fly.... Is your magic wand. |
Are sat dishes too small?
On Tue, 5 Jun 2012 14:30:18 +0100, PeterC
wrote: On Tue, 05 Jun 2012 10:07:55 +0100, Jeff Layman wrote: On 05/06/2012 08:53, Brian Gaff wrote: I ask this as some people I know who live here darn souf, seem to always get duff reception when the cloud cover is bad. OK I don't know enough about the location etc to comment, but there do seem to be a lot of people in forums etc complaining recently, and i just wondered if in order to make the dishes look smaller the gain has been paired to the bare minimum. Brian Did you mean to ask "Are Sky dishes too small?" I have always understood that the 45 cm Sky disk was the minimum size that Sky could get away with for (usually?) reliable reception. When I looked into getting Freesat a couple of years - or maybe more - ago, the minimum size of disk available relatively cheaply, complete with receiver, was 65 cm. Apart from having to move the dish because of a tree growing too high, I've never had reception problems from 28.5° here in Sussex, no matter what the cloud cover. I went for 65cm, just to be on the safe size. What is the reception like much further north, particularly in Scotland? That needs Skye dishes. Oh! ye'll take the high band and I'll take the low band, And I'll be in Scotland afore ye. I'll get ma kilt. Haste ye back! I've had ma tea. -- Graham. %Profound_observation% |
Are sat dishes too small?
"Brian Gaff" wrote in message ... I ask this as some people I know who live here darn souf, seem to always get duff reception when the cloud cover is bad. OK I don't know enough about the location etc to comment, but there do seem to be a lot of people in forums etc complaining recently, and i just wondered if in order to make the dishes look smaller the gain has been paired to the bare minimum. Brian 60cm works in most of the UK, but at least this is advisable in Scotland. As most installations are "free" from $ky and any front of house / chimney stack dishes are limited to 45cm, then this is the size they normally use. Pretty marginal for coverage especially on poor weather or if water gets in anywhere. |
Are sat dishes too small?
Brian Gaff wrote:
I ask this as some people I know who live here darn souf, seem to always get duff reception when the cloud cover is bad. OK I don't know enough about the location etc to comment, but there do seem to be a lot of people in forums etc complaining recently, and i just wondered if in order to make the dishes look smaller the gain has been paired to the bare minimum. The question is, what is meant by 'too small'? Too small for normal commercial standards of reliability, yes. Too small if the odd bit of rain fade can be tolerated now and then, no. Complaints about poor satellite reception always come down to dish misalignment, faulty LNB, faulty cable, faulty tuner, terrestrial interference. Bill |
Are sat dishes too small?
David Woolley wrote:
DSB dish sizes tend to be set by planning law. They are set based on what is permissible without explicit planning permission. The max size set by planning law significantly exceeds the range of mini-dish sizes. Bill |
Are sat dishes too small?
Jeff Layman wrote:
I have always understood that the 45 cm Sky disk was the minimum size that Sky could get away with for (usually?) reliable reception. When I looked into getting Freesat a couple of years - or maybe more - ago, the minimum size of disk available relatively cheaply, complete with receiver, was 65 cm. Apart from having to move the dish because of a tree growing too high, I've never had reception problems from 28.5° here in Sussex, no matter what the cloud cover. We find it helpful to use larger dish sizes for communal systems where there is a lot of amplification, because the increased s/n ratio (less beamwidth means less sky noise) means the amps aren't having to carry the whole bandful of noise at a high level. Also, really clean muxes can stand more amplifier noise. Bill |
Are sat dishes too small?
R. Mark Clayton wrote:
As most installations are "free" from $ky and any front of house / chimney stack dishes are limited to 45cm By what decree? Bill |
Are sat dishes too small?
On 05/06/2012 09:53, David Woolley wrote:
The satellite operators are constrained by the power from the photo cells on the satellites, but choose the technical parameters of their signals so as to get the maximum revenue (i.e. sell as many channels as possible) consistent with producing an acceptable signal most of the time. Increasing the bit rate on a multiplex means a higher signal to noise ratio is required to receive it accurately. Is that what they do? I assumed they kept the transponder symbol rate the same, but squeezed more channels into it - with a resulting continuous loss of quality as there are fewer bits per channel. I suppose you could fiddle with the symbol rate or error correction, but I'd be a little surprised. Andy |
Are sat dishes too small?
"Bill Wright" wrote in message ... R. Mark Clayton wrote: As most installations are "free" from $ky and any front of house / chimney stack dishes are limited to 45cm By what decree? Bill The Town and Country Planning (General Permitted Development) Order 1995 (H.1.a.i) but amended by The Town and Country Planning (General Permitted Development) Order 2005 http://www.communities.gov.uk/docume...drantennas.pdf the latter allowed 60cm NOT 45cm - so well spotted. |
Are sat dishes too small?
Andy Champ wrote:
Is that what they do? I assumed they kept the transponder symbol rate the same, but squeezed more channels into it - with a resulting continuous loss of quality as there are fewer bits per channel. That is what they do to choose the rate in the first place. They can then try and find the point that finds the best balance between number of chargeable channels and what people are prepared to pay for a given level of quality. First choose the fastest bit rate that produces a usable signal for enough of the time that the punters won't complain too much. This maximises the number of channels at a given technical quality. Then you can try reducing the quality until what people are prepared to pay starts off dropping faster than the bit rate per channel. |
Are sat dishes too small?
R. Mark Clayton wrote:
"Bill Wright" wrote in message ... R. Mark Clayton wrote: As most installations are "free" from $ky and any front of house / chimney stack dishes are limited to 45cm By what decree? Bill The Town and Country Planning (General Permitted Development) Order 1995 (H.1.a.i) but amended by The Town and Country Planning (General Permitted Development) Order 2005 http://www.communities.gov.uk/docume...drantennas.pdf the latter allowed 60cm NOT 45cm - so well spotted. and well known to dish installers, who often face florid-faced local ladies who see the new dish as they walk their pet rats and declare, "I'll send for the police!" Bill |
Are sat dishes too small?
Bill Wright wrote:
David Woolley wrote: DSB dish sizes tend to be set by planning law. They are set based on what is permissible without explicit planning permission. The max size set by planning law significantly exceeds the range of mini-dish sizes. There are two limits; one for the first aerial and one for the second. Are you referring to the smaller one. If so, I guess that there is a combination of people self policing the visual impact of the dish and also wanting to minimise the materials cost. |
Are sat dishes too small?
On Tue, 05 Jun 2012 22:03:08 +0100, Bill Wright wrote:
R. Mark Clayton wrote: "Bill Wright" wrote in message ... R. Mark Clayton wrote: As most installations are "free" from $ky and any front of house / chimney stack dishes are limited to 45cm By what decree? Bill The Town and Country Planning (General Permitted Development) Order 1995 (H.1.a.i) but amended by The Town and Country Planning (General Permitted Development) Order 2005 http://www.communities.gov.uk/docume...drantennas.pdf the latter allowed 60cm NOT 45cm - so well spotted. and well known to dish installers, who often face florid-faced local ladies who see the new dish as they walk their pet rats and declare, "I'll send for the police!" Bill y dish caused a lot of comment at first: I couldn't hear what was being said, but the number of people who stopped/pointed/talked...! It's not only 65cm (Only 5cm over permitted size) but pale cream and solid. Fortunately it's about 20m back from the road and the house is set back from the one next door, so the dish isn't visible for far along the road. It used to suffer loss of signal in v. bad weather, then I realised that I hadn't skewed the LNB. Since then there's been no problem at all. -- Peter. The gods will stay away whilst religions hold sway |
Are sat dishes too small?
"Bill Wright" wrote in message ... R. Mark Clayton wrote: "Bill Wright" wrote in message ... R. Mark Clayton wrote: As most installations are "free" from $ky and any front of house / chimney stack dishes are limited to 45cm By what decree? Bill The Town and Country Planning (General Permitted Development) Order 1995 (H.1.a.i) but amended by The Town and Country Planning (General Permitted Development) Order 2005 http://www.communities.gov.uk/docume...drantennas.pdf the latter allowed 60cm NOT 45cm - so well spotted. and well known to dish installers, who often face florid-faced local ladies who see the new dish as they walk their pet rats and declare, "I'll send for the police!" Bill In Scotland: 2 antennas maximum (fronting and non-fronting (these terms are not specifically used in the Order)) 1 antenna: up to 100cm and 35 litres cubic capacity. Other antennas: up to 60cm and 35 litres cubic capacity. Chimney-mounted antenna: up to 60cm and 35 litres cubic capacity I love teh idea of a dish having cubic capacity. |
Are sat dishes too small?
In article , Bill Wright
wrote: Jeff Layman wrote: I have always understood that the 45 cm Sky disk was the minimum size that Sky could get away with for (usually?) reliable reception. When I looked into getting Freesat a couple of years - or maybe more - ago, the minimum size of disk available relatively cheaply, complete with receiver, was 65 cm. Apart from having to move the dish because of a tree growing too high, I've never had reception problems from 28.5° here in Sussex, no matter what the cloud cover. We find it helpful to use larger dish sizes for communal systems where there is a lot of amplification, because the increased s/n ratio (less beamwidth means less sky noise) Erm... I'm puzzled by you saying a larger dish ("less beamwidth") means "less sky noise". I can see that a larger dish will have a higher gain, so should pick up more signal. But why do you say a larger dish will reduce sky noise? I'd expect the improvement in CNR to be due to more signal, not less sky noise. Although I can see that reducing the dish overspill may reduce the noise from what the feed sees around the rim of the dish (house, ground, whatever). Are you assuming a larger dish will also give a changed illumination factor? Slainte, Jim -- Please use the address on the audiomisc page if you wish to email me. Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html Audio Misc http://www.audiomisc.co.uk/index.html |
Are sat dishes too small?
Jim Lesurf wrote:
I'm puzzled by you saying a larger dish ("less beamwidth") means "less sky noise". I can see that a larger dish will have a higher gain, so should pick up more signal. But why do you say a larger dish will reduce sky noise? I'd expect the improvement in CNR to be due to more signal, not less sky noise. I'd agree with you. If there were no temperature variations, you would expect the amount of noise to be independent of the dish diameter. A smaller dish may see more warm buildings than a large one. Warm is relative; the sky is very cold. |
Are sat dishes too small?
On Wed, 6 Jun 2012 09:16:07 +0100, Geoff Pearson wrote:
In Scotland: 2 antennas maximum (fronting and non-fronting (these terms are not specifically used in the Order)) 1 antenna: up to 100cm and 35 litres cubic capacity. Other antennas: up to 60cm and 35 litres cubic capacity. Chimney-mounted antenna: up to 60cm and 35 litres cubic capacity I love teh idea of a dish having cubic capacity. Should have been given in micro-olympicswimmingpool units - or possibly use the Wok as a unit. -- Peter. The gods will stay away whilst religions hold sway |
Are sat dishes too small?
In article , David Woolley
wrote: Jim Lesurf wrote: I'm puzzled by you saying a larger dish ("less beamwidth") means "less sky noise". I can see that a larger dish will have a higher gain, so should pick up more signal. But why do you say a larger dish will reduce sky noise? I'd expect the improvement in CNR to be due to more signal, not less sky noise. I'd agree with you. If there were no temperature variations, you would expect the amount of noise to be independent of the dish diameter. Indeed. Although there may be other effects like the extent to which the feed sees itself, I assume. What puzzled me was the sweeping statement about "less beamwidth means less sky noise", though. A smaller dish may see more warm buildings than a large one. Warm is relative; the sky is very cold. Although that is true, I wonder if the feed sees rather more 'warm ground/buildings' due to the feed's field-of-view not being filled by the dish. Hence my question about illumination factor. FWIW I'm more used to systems like Cassegrain, though, where the overspill is also mainly onto the sky with most microwave designs I've known. Slainte, Jim -- Please use the address on the audiomisc page if you wish to email me. Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html Audio Misc http://www.audiomisc.co.uk/index.html |
Are sat dishes too small?
Geoff Pearson wrote:
In Scotland: 2 antennas maximum (fronting and non-fronting (these terms are not specifically used in the Order)) 1 antenna: up to 100cm and 35 litres cubic capacity. Other antennas: up to 60cm and 35 litres cubic capacity. Chimney-mounted antenna: up to 60cm and 35 litres cubic capacity I love teh idea of a dish having cubic capacity. This is measured in whisky of course. It's also important to remember that that a dish can exceed the sizes given above by 50% if it is painted using tartan paint. Bill |
Are sat dishes too small?
Jim Lesurf wrote:
In article , Bill Wright wrote: Jeff Layman wrote: I have always understood that the 45 cm Sky disk was the minimum size that Sky could get away with for (usually?) reliable reception. When I looked into getting Freesat a couple of years - or maybe more - ago, the minimum size of disk available relatively cheaply, complete with receiver, was 65 cm. Apart from having to move the dish because of a tree growing too high, I've never had reception problems from 28.5° here in Sussex, no matter what the cloud cover. We find it helpful to use larger dish sizes for communal systems where there is a lot of amplification, because the increased s/n ratio (less beamwidth means less sky noise) Erm... Got a bad throat Jim? That 'erm' that some people use, it means, "You're talking ********." It's like, "With all due respect." Don't do it. It's had its day, like ponytails on IT men and dungarees on lezzas. I'm puzzled by you saying a larger dish ("less beamwidth") means "less sky noise". I can see that a larger dish will have a higher gain, so should pick up more signal. But why do you say a larger dish will reduce sky noise? I'd expect the improvement in CNR to be due to more signal, not less sky noise. Less area of sky received. Same area of satellite tx dish visible. Improved ratio. Although I can see that reducing the dish overspill may reduce the noise from what the feed sees around the rim of the dish (house, ground, whatever). Are you assuming a larger dish will also give a changed illumination factor? No, I'm basing my remarks on various publications used in the industry. Bill |
Are sat dishes too small?
"PeterC" wrote in message
... On Wed, 6 Jun 2012 09:16:07 +0100, Geoff Pearson wrote: In Scotland: 2 antennas maximum (fronting and non-fronting (these terms are not specifically used in the Order)) 1 antenna: up to 100cm and 35 litres cubic capacity. Other antennas: up to 60cm and 35 litres cubic capacity. Chimney-mounted antenna: up to 60cm and 35 litres cubic capacity I love teh idea of a dish having cubic capacity. Should have been given in micro-olympicswimmingpool units - or possibly use the Wok as a unit. Can't you use a wok as a dish? -- Max Demian |
Are sat dishes too small?
In article , Bill Wright
wrote: Jim Lesurf wrote: We find it helpful to use larger dish sizes for communal systems where there is a lot of amplification, because the increased s/n ratio (less beamwidth means less sky noise) I'm puzzled by you saying a larger dish ("less beamwidth") means "less sky noise". I can see that a larger dish will have a higher gain, so should pick up more signal. But why do you say a larger dish will reduce sky noise? I'd expect the improvement in CNR to be due to more signal, not less sky noise. Less area of sky received. Same area of satellite tx dish visible. Improved ratio. Which isn't the same as saying that a " smaller beamwidth means less *sky noise* ". The actual level of sky noise may not change much when you change the beam width. Depends on what is in the field(s) of view. The CNR may well change for reasons that don't require any alteration in "sky noise" when the "beamwidth" is altered. The most obvious being change of the signal level. Although I can see that reducing the dish overspill may reduce the noise from what the feed sees around the rim of the dish (house, ground, whatever). Are you assuming a larger dish will also give a changed illumination factor? No, I'm basing my remarks on various publications used in the industry. That opens up the possibility that some "industry" "publications" are either poorly worded, or that you haven't quoted them accurately. As someone else has already agreed here, if the 'sky' has a fairly uniform radiation temperature then changing the "beamwidth" may have little effect on the "sky noise" level. What may well change is the signal power collected from the source, of course. And you may get noise that is *not* from the "sky". Can you quote/cite one or two parts in the industry publications you have in mind that I can read on the web? I'd be interested to see where they say what you are telling us they do. Since textbooks often contain mistakes I can understand other publications having misleading wordings, etc. So maybe they are mis-ascribing changes in CNR to changes in "sky noise" when other reasons are the cause. Slainte, Jim -- Please use the address on the audiomisc page if you wish to email me. Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html Audio Misc http://www.audiomisc.co.uk/index.html |
Are sat dishes too small?
Jim Lesurf wrote:
That opens up the possibility that some "industry" "publications" are either poorly worded, or that you haven't quoted them accurately. As someone else has already agreed here, if the 'sky' has a fairly uniform radiation temperature then changing the "beamwidth" may have little effect on the "sky noise" level. What may well change is the signal power collected from the source, of course. And you may get noise that is *not* from the "sky". Can you quote/cite one or two parts in the industry publications you have in mind that I can read on the web? Just leaving this aside while I find a minute to have a look through some CAI publications, what's your view on my statement (might have only implied it; can't remember) that on a system with a lot of amplification a better c/n ratio has the (additional) benefit that with the full bandwidth of noise reduced relative to the signal it should be possible to obtain higher max signal output from the amps? Bill |
Are sat dishes too small?
In article , Bill Wright
wrote: Jim Lesurf wrote: That opens up the possibility that some "industry" "publications" are either poorly worded, or that you haven't quoted them accurately. As someone else has already agreed here, if the 'sky' has a fairly uniform radiation temperature then changing the "beamwidth" may have little effect on the "sky noise" level. What may well change is the signal power collected from the source, of course. And you may get noise that is *not* from the "sky". Can you quote/cite one or two parts in the industry publications you have in mind that I can read on the web? Just leaving this aside while I find a minute to have a look through some CAI publications, what's your view on my statement (might have only implied it; can't remember) that on a system with a lot of amplification a better c/n ratio has the (additional) benefit that with the full bandwidth of noise reduced relative to the signal it should be possible to obtain higher max signal output from the amps? The above question is a bit long, and has many clauses, so I hesitate as I'm not certain I've understood it. Are you asking if high CNR at input probably means the noise power can be neglected when assessing how much gain you can apply before the output reaches a given (clipping) level? If the above is what you mean, then the answer is "yes" in principle, on the basis that essentially all of the max output power and voltage should be available for the signal. But you might need a fair CNR for the effect to be significant. As usual it depends on the details. If I've misunderstood the question then you'd have to clarify. Slainte, Jim -- Please use the address on the audiomisc page if you wish to email me. Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html Audio Misc http://www.audiomisc.co.uk/index.html |
Are sat dishes too small?
On 05/06/12 10:07, Andy Burns wrote:
David Woolley wrote: Sky zone1 elliptical dishes are considerably smaller than the 1m dishes usually allowed without planning permission. Bring back the squarial. Wasn't that just an array of grid antennas? in a white square box? |
Are sat dishes too small?
On 06/06/12 09:34, Jim Lesurf wrote:
In , Bill Wright wrote: Jeff Layman wrote: I have always understood that the 45 cm Sky disk was the minimum size that Sky could get away with for (usually?) reliable reception. When I looked into getting Freesat a couple of years - or maybe more - ago, the minimum size of disk available relatively cheaply, complete with receiver, was 65 cm. Apart from having to move the dish because of a tree growing too high, I've never had reception problems from 28.5° here in Sussex, no matter what the cloud cover. We find it helpful to use larger dish sizes for communal systems where there is a lot of amplification, because the increased s/n ratio (less beamwidth means less sky noise) Erm... I'm puzzled by you saying a larger dish ("less beamwidth") means "less sky noise". I can see that a larger dish will have a higher gain, so should pick up more signal. But why do you say a larger dish will reduce sky noise? I'd expect the improvement in CNR to be due to more signal, not less sky noise. Larger dishes are more directional, e.g. you need to aim them more accurately but get a commensurately higher gain. Smaller dishes are less directional so have a wider beamwidth. Think about telescopes/binoculars/magnifying glasses. The bigger the lens the more you are able to "zoom" and pick up more detail from your intended target, but the more accurate you have to aim. |
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