What size of dish do I need?
James Bryant
Go with the largest you can handle.
Not only do you get a better look angle, but just as important, if not more
so, is the increase in signal gain figures. This matters a lot during those
winter months.
It can dictate how often you have to clean out that dish.
--
James Bryant
aka: The Uplinker
http://theuplinker.com
R. Rikoski
Disagree. Bigger is not better when it comes to Ku as the dish has to
be aligned more precisely when being set up and stopped right on the
money each time that you go to a Ku satellite. This is because of the
narrower beam of the larger diameter, higher gain dish.
Bigger dishes present a greater wind load too, so the mast has to be
anchored better. Bigger dishes have to be assembled with precision
otherwise the gain, even on C band drops to that of the next-sized
smaller dish and worse, for satellites with 2 degree separation, the
sidelobes come up with resulting cross-talk from adjacent satellites.
Because of these factors, the optimal size for non-professional mesh
dishes has to be somewhere between 8 1/2 to 10 1/2 feet.
In article <%o827.5615$6O3.3...@newsread1.prod.itd.earthlink.net>,
Mike S
"R. Rikoski" wrote:
>
> Disagree. Bigger is not better when it comes to Ku as the dish has to
> be aligned more precisely when being set up and stopped right on the
> money each time that you go to a Ku satellite. This is because of the
> narrower beam of the larger diameter, higher gain dish.
Yup, agreed. But this also increases your gain which is very much
needed when catching uplinks from remote news trucks and other weak
feeds. So, you need a receiver and actuator that can do accurate dish
positioning. Readilly available. Not rocket science. And desirable in
any event. It's only an issue when first hunting for the Ku sat and
once nailed, it's nailed.
>
> Bigger dishes present a greater wind load too, so the mast has to be
> anchored better. Bigger dishes have to be assembled with precision
> otherwise the gain, even on C band drops to that of the next-sized
> smaller dish and worse, for satellites with 2 degree separation, the
> sidelobes come up with resulting cross-talk from adjacent satellites.
I have a 9 ft. SOLID aluminum dish. It has no assembly. It doesn't warp.
It's properly mounted on a properly secured 3.5" post and hasen't moved
in 10 years through numerous storms with 60-70 MPh wind gusts. As for
sidelobes, a fairly well beat-up big dish has smaller sidelobes than a
perfect 6' dish.
>
> Because of these factors, the optimal size for non-professional mesh
> dishes has to be somewhere between 8 1/2 to 10 1/2 feet.
Nope, I still maintain bigger is better.
Mike S
R. Rikoski
<NoS...@this.address.com> wrote:
> See comments embedded.
>
> "R. Rikoski" wrote:
> >
> > Disagree. Bigger is not better when it comes to Ku as the dish has to
> > be aligned more precisely when being set up and stopped right on the
> > money each time that you go to a Ku satellite. This is because of the
> > narrower beam of the larger diameter, higher gain dish.
>
> Yup, agreed. But this also increases your gain which is very much
> needed when catching uplinks from remote news trucks and other weak
> feeds. So, you need a receiver and actuator that can do accurate dish
> positioning.
No question about it if the viewer needs the gain for "weak" newsfeeds.
But did the poser of the question, or most other big dish users for
that matter, intend to chase weak newsfeeds or was that something that
you thought would be a good thing to do even at the expense of the
added hassle of a really large (to me, a 12 foot and larger) dish.
> Readilly available. Not rocket science.
Science is not the issue here. Engineering complexity, cost and
reliability are.
And desirable in
> any event.
You keep saying that.
It's only an issue when first hunting for the Ku sat and
> once nailed, it's nailed.
With any slop in the actuator, and all actuators, even my two horizon
to horizon mounted dishes have slop; you will have to go back and forth
to hit the center of the Ku signal. If you are chasing "weak newsfeeds"
this is a probably a minor issue to you, if you just want to point and
shoot, like with a 4DTV receiver, it is a nuisance.
But since your dish is only 9 feet, this problem probably hasn't been
too noticible to you. Go up even one size to a 10 1/2 and I guarantee
you will experience it, no matter how carefully you do your
installation.
> >
> > Bigger dishes present a greater wind load too, so the mast has to be
> > anchored better. Bigger dishes have to be assembled with precision
> > otherwise the gain, even on C band drops to that of the next-sized
> > smaller dish and worse, for satellites with 2 degree separation, the
> > sidelobes come up with resulting cross-talk from adjacent satellites.
>
> I have a 9 ft. SOLID aluminum dish. It has no assembly. It doesn't warp.
> It's properly mounted on a properly secured 3.5" post and hasen't moved
> in 10 years through numerous storms with 60-70 MPh wind gusts.
Most readily bought large dishes are mesh.
But let me see if I have this right: you have suggested that bigger is
better; you told the questioner that he should get the largest dish
that he could; you took exception to my suggestion that the optimal
size for a dish was somewhere between 8 1/2 to 10 1/2 feet, yet your
own dish, at 9 feet, falls right in the range that I suggested? So what
is your basis for arguing that bigger is better?
As for
> sidelobes, a fairly well beat-up big dish has smaller sidelobes than a
> perfect 6' dish.
Well, both are pretty awful and on some C band transponders, unusable
for the crosstalk from a transponder on an adjacent 2 degree satellite.
What would be the point of erecting a larger dish in this instance? The
small one is easy to put up and align and would not have to be aimed
precisely to get identical results.
You might want to take a look at the ARRL Antenna Handbook for
parabolic dishes. There is a graph that shows that tolerances on
surface irregularities are pretty severe on parabolic dishes. Gain
reduction gets much worse as the reflector size increases. Look it up.
A quarter of an inch is a lot.
>
> >
> > Because of these factors, the optimal size for non-professional mesh
> > dishes has to be somewhere between 8 1/2 to 10 1/2 feet.
>
> Nope, I still maintain bigger is better.
If you say so, Mike. But you are being pretty vague.
Two questions: How big did you really have in mind? You didn't say,
only that you thought your 9 foot solid was yummy. (Which I agree with,
completely).
Secondly, Where is there a readily available supplier (not a source
only known to a rocket scientist with a federally funded project
budget) that a poster to this newsgroup might obtain a really large,
non-mesh dish?
Enjoyed talking with you Mike. BTW, I like solid dishes too.
I once had a solid 8 footer that I got from the railroad. It was my
second personal satellite dish, after a 10 1/2 foot Prodelin that took
4 guys and 18 bags of Sakrete to install. I was lucky enough to get a
spun aluminum dish that wasn't out of shape because I would have had a
devil of a time bending it back into parabolic.
It worked well except for terrestrial interference. I was right in the
path of an ATT phone beam to downtown Chicago. The solid dish didn't
reject that very well. Something about shallowness and diffraction from
the edge of the dish. I learned about microwave filters from that
experience and happily left that problem behind, and the railroad dish
too, when I moved. But that's another story.
Rick
Mike S
I am enjoying the discussion also, so let me point out that I
answer in that interest, lest anyone accuse one of us of beating the
proverbial dead horse.
> No question about it if the viewer needs the gain for "weak" newsfeeds.
> But did the poser of the question, or most other big dish users for
> that matter, intend to chase weak newsfeeds or was that something that
> you thought would be a good thing to do even at the expense of the
> added hassle of a really large (to me, a 12 foot and larger) dish.
Ok, the need to quest for weak Ku signals is my opinion, point taken.
But the original poster did not specify his wants or needs, maybe
doesn't have any yet because of lack of experience. It is my belief
that sooner or later ALL BUD users will chase an occasional weak signal,
if for no other reason than to try it once.
However, your assertion that 12 foot and larger dishes are an added
hassle is YOUR opinion. We have conflicting opinions.
> > Readilly available. Not rocket science.
>
> Science is not the issue here. Engineering complexity, cost and
> reliability are.
This was a retort to your "added hassle" opinion. My point was that
even cheap, used gear from Ebay can point a large dish at a Ku sat
within a click or two, it's not a problem.
> It's only an issue when first hunting for the Ku sat and
> > once nailed, it's nailed.
>
> With any slop in the actuator, and all actuators, even my two horizon
> to horizon mounted dishes have slop; you will have to go back and forth
> to hit the center of the Ku signal. If you are chasing "weak newsfeeds"
> this is a probably a minor issue to you, if you just want to point and
> shoot, like with a 4DTV receiver, it is a nuisance.
If you get within a click or two, point and shoot works fine, even on
Ku. Even on digital. (I use a 4DTV 922 receiver these days, still have
my trusty Uniden SQ-590 warmed up). Other than that, nudging the dish
back and forth, or the skew this way and that, in order to chase a weak
signal is, well, chasing it!
> But since your dish is only 9 feet, this problem probably hasn't been
> too noticible to you. Go up even one size to a 10 1/2 and I guarantee
> you will experience it, no matter how carefully you do your
> installation.
Oh, I notice it. There is a known bug in the 4DTV concerning accurate
positioning of Ku Sats. But again, it's not the big hassle you seem to
make it out to be.
> But let me see if I have this right: you have suggested that bigger is
> better; you told the questioner that he should get the largest dish
> that he could; you took exception to my suggestion that the optimal
> size for a dish was somewhere between 8 1/2 to 10 1/2 feet, yet your
> own dish, at 9 feet, falls right in the range that I suggested? So what
> is your basis for arguing that bigger is better?
Because _I_ really lust for bigger. If I could figure a way to manage
it, I'd really like a 15 METER dish on an H-H or maybe even an AZ/EL
mount with clear sky over the entire satellite arc!! Ever see a dish at
a commercial uplink facility? Yup, that's it!! Other than that, your
point is well taken. <G>
>
> As for
> > sidelobes, a fairly well beat-up big dish has smaller sidelobes than a
> > perfect 6' dish.
>
> Well, both are pretty awful and on some C band transponders, unusable
> for the crosstalk from a transponder on an adjacent 2 degree satellite.
>
> What would be the point of erecting a larger dish in this instance? The
> small one is easy to put up and align and would not have to be aimed
> precisely to get identical results.
There's no real case study I'm aware of on this, but lots of hearsay
evidence on the newsgroups from users with various sized dishes. The
biggest problem appears to be capturing SOME digital channels using a
4DTV. In order to reliably get these channels, one needs adequate gain
AND the ability to avoid adjacent sat interference. My general
observation is that folks with 6 footers, no matter how well
constructed, solid or mesh, can't hack it. (Even their analog reception
suffers because they mention the "picture behind the picture" effect)
Folks with 7.5 footers seem to be on the edge with some success and some
failure probably having a lot to do with location within the footprint
and a finely tweaked dish. Folks with 9-12 foot dishes, solid OR mesh,
who seem savvy enough to have them set up right, have no problems at all
with these signals.
> You might want to take a look at the ARRL Antenna Handbook for
> parabolic dishes. There is a graph that shows that tolerances on
> surface irregularities are pretty severe on parabolic dishes. Gain
> reduction gets much worse as the reflector size increases. Look it up.
> A quarter of an inch is a lot.
I believe that. Misaligned surfaces do worse than not collect signal,
they actually send "anti-signal" to the focal point thus canceling out
an equal sized area of the dish which IS aligned.
> > > Because of these factors, the optimal size for non-professional mesh
> > > dishes has to be somewhere between 8 1/2 to 10 1/2 feet.
> >
> > Nope, I still maintain bigger is better.
>
> If you say so, Mike. But you are being pretty vague.
No, I'm being stubborn! There's a difference! <G>
Actually, I was deliberately overstating my case. We have so much
competition from the little dishes these days and Joe Average can't help
but hold them up as a comparison to C band. If I just said a 7.5 was
marginal and an 8 foot was great, the original poster might just weigh
in with his inexperienced wishes and go for that 6 footer! Then he ends
up spending lots of time and money on a system that has no real chance
of performing like C band does, and we lose another subscriber to the
pizza plates.
On the other hand, if I say bigger the better, 20 meter if you can get
it, that 6 footer starts to look less likely to succeed. Oh, and I have
never heard any owner of any BIG dish say "Gosh, I wish this thing was
smaller!" except in the context of moving one.
> Two questions: How big did you really have in mind? You didn't say,
> only that you thought your 9 foot solid was yummy. (Which I agree with,
> completely).
See above.
>
> Secondly, Where is there a readily available supplier (not a source
> only known to a rocket scientist with a federally funded project
> budget) that a poster to this newsgroup might obtain a really large,
> non-mesh dish?
Saw a 9 METER dish posted in the newsgroups as a come-n-getit. Was
sorely tempted. Yes it WAS 9 METERS. I have a neighbor across the
alley with a big solid dish, maybe even 12 feet. But it's shiny
aluminum. I suspect it bakes LNB's at the solstice. And it's pointed
north, so I bet I could talk him out of it if I wanted to bake some
LNB's. <G> Also, there's nothing wrong with a well constructed mesh
dish and those are available new if not cheap.
>
> Enjoyed talking with you Mike. BTW, I like solid dishes too.
>
> I once had a solid 8 footer that I got from the railroad. It was my
> second personal satellite dish, after a 10 1/2 foot Prodelin that took
> 4 guys and 18 bags of Sakrete to install. I was lucky enough to get a
> spun aluminum dish that wasn't out of shape because I would have had a
> devil of a time bending it back into parabolic.
Hmm, 4 guys and 18 bags of Sakrete. I'm beginning to understand your
"hassle" opinion. <G> At least the dish itself was a freebee. (yes?)
> It worked well except for terrestrial interference. I was right in the
> path of an ATT phone beam to downtown Chicago. The solid dish didn't
> reject that very well. Something about shallowness and diffraction from
> the edge of the dish. I learned about microwave filters from that
> experience and happily left that problem behind, and the railroad dish
> too, when I moved. But that's another story.
Chicago, hey? Not to far from Ft. Wayne, IN. where I am.
Regards,
Mike
R. Rikoski
<NoS...@this.address.com> wrote:
> Hi Rick,
>
> I am enjoying the discussion also, so let me point out that I
> answer in that interest...
>
>It is my belief
> that sooner or later ALL BUD users will chase an occasional weak signal,
> if for no other reason than to try it once.
Then they should put up a big one as their next dishes.
>
> However, your assertion that 12 foot and larger dishes are an added
> hassle is YOUR opinion. We have conflicting opinions.
Have you ever put one up?
>
> My point was that
> even cheap, used gear from Ebay can point a large dish at a Ku sat
> within a click or two, it's not a problem.
Big dish: big problem. It has to be spot-on to get the gain that made
you go for the big one in the first place. With high gain comes narrow
beamwidth.
> > But let me see if I have this right: you have suggested that bigger is
> > better; you told the questioner that he should get the largest dish
> > that he could; you took exception to my suggestion that the optimal
> > size for a dish was somewhere between 8 1/2 to 10 1/2 feet, yet your
> > own dish, at 9 feet, falls right in the range that I suggested? So what
> > is your basis for arguing that bigger is better?
>
> Because _I_ really lust for bigger. If I could figure a way to manage
> it, I'd really like a 15 METER dish on an H-H or maybe even an AZ/EL
> mount with clear sky over the entire satellite arc!! Ever see a dish at
> a commercial uplink facility? Yup, that's it!!
I understand. That's you and maybe Joe Six-Pack, too or maybe, not.
>
> >
> There's no real case study I'm aware of on this, but lots of hearsay
> evidence on the newsgroups from users with various sized dishes. The
> biggest problem appears to be capturing SOME digital channels using a
> 4DTV. In order to reliably get these channels, one needs adequate gain
> AND the ability to avoid adjacent sat interference. My general
> observation is that folks with 6 footers, no matter how well
> constructed, solid or mesh, can't hack it. (Even their analog reception
> suffers because they mention the "picture behind the picture" effect)
That is because their beamwidth is too wide and the sidelobes are
significant.
This has been known for at least 50 years. Any antenna text will tell
you this. It is a matter of physics, not he said-she said.
>
> Folks with 7.5 footers seem to be on the edge with some success and some
> failure probably having a lot to do with location within the footprint
> and a finely tweaked dish.
True. One of my 4DTV's is hooked to a five foot mesh. (HH mount; 15
degree and 0.5db lnb's; ADL c/ku horn).
> Folks with 9-12 foot dishes, solid OR mesh,
> who seem savvy enough to have them set up right, have no problems at all
> with these signals.
Yup.
>
> > You might want to take a look at the ARRL Antenna Handbook for
> > parabolic dishes. There is a graph that shows that tolerances on
> > surface irregularities are pretty severe on parabolic dishes. Gain
> > reduction gets much worse as the reflector size increases. Look it up.
> > A quarter of an inch is a lot.
>
> I believe that. Misaligned surfaces do worse than not collect signal,
> they actually send "anti-signal" to the focal point thus canceling out
> an equal sized area of the dish which IS aligned.
Yup.
> Actually, I was deliberately overstating my case. We have so much
> competition from the little dishes these days and Joe Average can't help
> but hold them up as a comparison to C band.
Ah well, so they leave. Lettum go. Maybe this hobby belongs to the
hard-core guys.
I have
> never heard any owner of any BIG dish say "Gosh, I wish this thing was
> smaller!" except in the context of moving one.
Or finding the money for one or taking a used one apart and
reassembling it or moving one by helicopter when the pilot has to drop
the dish because his engine is overheating.
> Saw a 9 METER dish posted in the newsgroups as a come-n-getit. Was
> sorely tempted. Yes it WAS 9 METERS. I have a neighbor across the
> alley with a big solid dish, maybe even 12 feet. But it's shiny
> aluminum. I suspect it bakes LNB's at the solstice.
Equinoxes.
And it's pointed
> north,
Maybe he is tracking the Molnya orbit Russian satellites.
so I bet I could talk him out of it if I wanted to bake some
> LNB's. <G> Also, there's nothing wrong with a well constructed mesh
> dish and those are available new if not cheap.
Yup.
> >
> > Enjoyed talking with you Mike. BTW, I like solid dishes too.
> >
> > I once had a solid 8 footer that I got from the railroad. It was my
> > second personal satellite dish, after a 10 1/2 foot Prodelin that took
> > 4 guys and 18 bags of Sakrete to install. I was lucky enough to get a
> > spun aluminum dish that wasn't out of shape because I would have had a
> > devil of a time bending it back into parabolic.
>
> Hmm, 4 guys and 18 bags of Sakrete. I'm beginning to understand your
> "hassle" opinion. <G> At least the dish itself was a freebee. (yes?)
No I bought it at the CES; a Bowman receiver; a Bowman C band feedhorn
and a 120 degree, C band LNB; all for $1000. New. Dealers price. 1983.
>
> > It worked well except for terrestrial interference. I was right in the
> > path of an ATT phone beam to downtown Chicago. The solid dish didn't
> > reject that very well. Something about shallowness and diffraction from
> > the edge of the dish. I learned about microwave filters from that
> > experience and happily left that problem behind, and the railroad dish
> > too, when I moved. But that's another story.
>
> Chicago, hey? Not to far from Ft. Wayne, IN. where I am.
I take it you go to the November hamfest, then?
Rick
>
> Regards,
> Mike
James Bryant
Let's face it. You both put forth valid arguments.
Many factors enter into a decision on dish size.
Utilization - What are you going to use the dish for?
Wild feed searches, or 4DTV?
Geographical - How far are you from the equator. A smaller dish does just
fine down in Fla, TX or AZ.
Not so well in OR, IL, MA, NY
Did you plant that tree before or after you installed the dish?
Weather - Do you live somewhere where rain and snow are a factor much of the
year. Massive thunderheads between you and the satellite can degrade Ku,
especially the digital receive side, enough to make it unusable,
commercially at least.
Do you live in a high wind risk area. Tornado alley doesn't need 5 meter
dishes sailing on the wind.
Did you consider wind when you chose your location for the dish. DUH!
Worst case scenario in a wind situation is to provide a windbreak, natural
or otherwise.
Chasing weak signals isn't always the need. What if you want the gain to
increase your reception on those edge of footprint birds?
Crosstalk - That's what RF filters and clamps are for.
Crosstalk on many receivers is horrible. You get what you pay for most of
the time. Avcom makes a spectrum analyzer that is portable and can run on
battery, but it's not much good for serious work. It can't hold a candle to
a good HP SpecAN
What I'm saying is that crosstalk can be more of a receiver/lnb quality
problem than a dish size factor.
Lower end receivers contribute to a lot of problems in that they aren't as
discrete as they could be.
Ok, chew on it some more.
Mike S
<snip>
> > Chicago, hey? Not to far from Ft. Wayne, IN. where I am.
>
> I take it you go to the November hamfest, then?
I try to. Sometimes I make it and sometimes not. My big hamfest is
Dayton in mid-may. Used to see a lot more sat stuff there than I did
this year. (OOTC) Last year there was a guy selling DMT1000 MPEG
receivers out of the back of a truck. He claimed they were all
programmed up for the currently available channels. Nearly bought one.
Didn't see him there this year. Just as well, I'm holding out for a
consumer rig that's 4:2:2 capable and does AC3 sound.
Mike
PhxGrunge
"James Bryant" <theup...@earthlink.net> wrote in message
news:car27.2130$HV1.2...@newsread1.prod.itd.earthlink.net...
> Gentlemen,
>
> Let's face it. You both put forth valid arguments.
>
> Many factors enter into a decision on dish size.
> Utilization - What are you going to use the dish for?
> Wild feed searches, or 4DTV?
>
> Geographical - How far are you from the equator. A smaller dish does
just
> fine down in Fla, TX or AZ.
> Not so well in OR, IL, MA, NY
> Did you plant that tree before or after you installed the dish?
No. Wrong information. You need at least a 8-12 ft dish in Arizona -
probably Fla & TX as well. The satellites are physically aimed at the
mid-west (Kansas, Missouri area). I know of many bud owners that started
out with a 6 ft dish here and quickly went to 10 ft because the 6 can't even
hack it in C-band. KU is weak here, very hard to chase any wild news feeds,
have to stick to C-band for that.
Eric
> Geographical - How far are you from the equator. A smaller dish does just
> fine down in Fla, TX or AZ.
> Not so well in OR, IL, MA, NY
Most of the North American aimed satellites have their footprints centered
on the central U.S. (i.e., Kansas) not at the equator. Florida actually
demands a larger dish than does Illinois in most instances.
http://www.panamsat.com/sat/beam/g3rcband.pdf
http://www.panamsat.com/sat/beam/g5cband.pdf
http://www.panamsat.com/sat/beam/g6cband.pdf
etc...
--
Better than hearing "Lady Day", or checking in at Monterey...
[Remove bodies from address for email.]
James Bryant
live up around Flagstaff on occasion). Small dishes tend to lose
attenuation faster than those boats.
rik...@earthlink.net
James Bryant <theup...@earthlink.net> wrote:
Heavy snow distorts the shape of the dish, so with a heavy snow cover
sticking to the dish, the gain of big mesh dishes goes down
proportionately more than smaller dishes
As it is with the smaller dishes, the signal has to go through the snow
twice but also the shape of a mesh reflector is no longer parabolic.
This is more noticible on a big dish because the smaller reflectors are
stiffer.
The sidelobes then go up also.
Bill Jones
> > Yes, but you don't deal with feet of snow in Florida or Arizona, (unless you
> > live up around Flagstaff on occasion). Small dishes tend to lose
> > attenuation faster than those boats.
>
> Heavy snow distorts the shape of the dish, so with a heavy snow cover
> sticking to the dish, the gain of big mesh dishes goes down
> proportionately more than smaller dishes
>
> As it is with the smaller dishes, the signal has to go through the snow
> twice but also the shape of a mesh reflector is no longer parabolic.
> This is more noticible on a big dish because the smaller reflectors are
> stiffer.
I agree with what you say here, re big dishes being more trouble in
snow, but I think it is simply the weight of the snow changing the AIM
rather than the SHAPE. Ie the whole dish moves down. I'm sure that
both occur, but I'm convinced that aim changes more. This is exactly
the same as the trick people use to see if their dish is off on
alignment, ie pulling down on the edge of the dish. Ie the whole dish
moves, and usually you can get a better signal, which wouldn't be the
case if you were distorting the dish.
In addition to the little dishes being stiffer, the beamwidth is
wider, so it doesn't matter so much if the aim is off.
Mike S
The highband GHz signal from the sat does not go thru the snow twice to
get to the feedhorn, it doesn't go through the snow at all. It reflects
off the surface (with some absorption). Anything that gets past the
surface is quickly scattered and absorbed. If it won't go through
widely scattered drops of water (rain fade) it certainly isn't going to
go through densely packed frozen water. The surface of the snow
sticking to the dish becomes the new surface of the dish. Yes the
"shape" of the dish is now different as far as the signal is concerned,
but the real, mechanical shape of the actual dish doesn't change much at
all. The size of the dish doesn't matter except for the effect on the
efficiency of snow collection. Big solid dishes can get warm enough
that the snow slides right out and plops on the ground. Not likely with
a mesh dish.
Also, because snow collects in patterns, i.e. in the bottom half of the
dish for example, you can mess up one polarity really bad and leave the
other almost untouched.
Mike S
rik...@earthlink.net
<NoS...@this.address.com> wrote:
> Buzzz! Ya both missed it, but thanks for playing! <G>
Wrong again!
On C band, there is very little signal loss in the snow; on ku; some
but not 100%.
>
> The highband GHz signal from the sat does not go thru the snow twice to
> get to the feedhorn, it doesn't go through the snow at all. It reflects
> off the surface (with some absorption). Anything that gets past the
> surface is quickly scattered and absorbed.
"Quickly" ??? I'll say, the speed of propagation is about the speed of
light. Hard to get quicker than that!
If it won't go through
> widely scattered drops of water (rain fade) it certainly isn't going to
> go through densely packed frozen water.
Well, it does get through "widely scattered drops of water". In rain
fade, the band of moisture that the signal travels through is at least
a km. thick. The snow on the dish is, maybe 10 cm. Hardly the same
thing.
The surface of the snow
> sticking to the dish becomes the new surface of the dish.
Not that simple.
Yes the
> "shape" of the dish is now different as far as the signal is concerned,
> but the real, mechanical shape of the actual dish doesn't change much at
> all.
Wrong again. The dish shape changes and it sags. So the beam doesn't
hit the center of the feed horn.
The size of the dish doesn't matter except for the effect on the
> efficiency of snow collection. Big solid dishes can get warm enough
> that the snow slides right out and plops on the ground.
I wish my 10 1/2 footers did that after Lake effect snow storms.
>
> Also, because snow collects in patterns, i.e. in the bottom half of the
> dish for example, you can mess up one polarity really bad and leave the
> other almost untouched.
Duh...What you say?
Eric
Snow in itself doesn't attenuate a C-band signal.
This is all irrelevant to your "equator" statement.
Eric
> Buzzz! Ya both missed it, but thanks for playing! <G>
>
> The highband GHz signal from the sat does not go thru the snow twice to
> get to the feedhorn, it doesn't go through the snow at all. It reflects
> off the surface (with some absorption). Anything that gets past the
> surface is quickly scattered and absorbed. If it won't go through
> widely scattered drops of water (rain fade) it certainly isn't going to
> go through densely packed frozen water.
If you look *real* closely, you can see the methane gas rising above
this post.
Snow has no attenuation properties for C-band signals, unless it is
metallic snow. Snow has no reflective properties for C-band signals,
unless it is metallic snow.
--
Better than hearing "Lady Day", or checking in at Monterey...
[Remove bodies from address for email.]
"Please don't eat the yellow snow."
Eric
C-band signals, why don't you post it?
Because you don't, that's why.
urr...@home.boy wrote:
> >~~~~~~~~~~~~ methane gas from below bs ~~~~~~~~~~~
>
> >If you look *real* closely, you can see the methane gas rising above
> >this post.
>
> You got that right.
>
> >~~~~~~~~~~~~ more methane gas from below bs ~~~~~~~~~~~
Mike S
it's surface, I get NO signals. Nada. nothing. It's a very solid
aluminum dish and very securely mounted. You couldn't warp this sucker
with a sledgehammer let alone snow. When there is no signal, pushing up
or down doesn't do squat, probably because whatever focal "point" that
remains is nowhere near the feedhorn due to the new shape of the
reflecting surface. Using a push broom to drag the snow off the dish
instantly restores a full and complete signal.
Mind you, we're not talking about absorption by snowflakes drifting
loosely through the air, we're talking packed snow. And as anyone who's
ever used a microwave oven can tell you, water absorbs microwaves.
Eric
> And as anyone who's
> ever used a microwave oven can tell you, water absorbs microwaves.
Completely differently frequencies. Microwave ovens don't run at
C-band frequencies.
Your problem lies elsewhere.
Bill Jones
> If you have a source that says snow does indeed attenuate and reflect
> C-band signals, why don't you post it?
>
arguments here, although some arguments have more truth to them than
others. :-)
Snow may reflect the signals to some small extent, much as some of
the light that hits a window is reflected back, however most of it goes
through into the snow. Of that that goes into the snow, some will be
absorbed and some will pass through. If the snow is thick enough, all
of the signal will be absorbed, but a couple inches on C-band will not
absorb all of it. Much the same as seeing the sunlight under water. Ie
the water absorbs some of the light, but in shallow water you can see
pretty well. In very deep water, all of the light will eventually be
absorbed. At C-band freqs, the absorption is greater than with visible
light, but generally most of the signal is not absorbed or reflected by
thin layers of snow, however if there is enough water present, it will
all be absorbed. I "think" there is more absorption at Ku freqs,
because I have seen the signal on little DBS dishes go out with only
about 1/4" of "slush" on the plastic LNB cover (compared to the signal
not going away when 1/4" of plywood is put in front of the LNB).
Relative to snow on a dish becoming the new reflective surface, as
Eric says, that is just simply wrong. What the snow does is diffract
(?sp?) (change the direction of the signal when particals are an
appropriate size and spacing relative to the wavelength) and refract
(change the direction like a lense) and absorb, much like dirty
sunglasses. Ie mainly two things, it will change the direction of the
signal a bit, and absorb some of it. Snow on a dish is like a mirror
fogged up by a shower. A little bit of snow will attenuate the signal,
but not kill it.
However the weight of the snow will usually pull the aim of the
dish off the signal, and kill the signal before absorption will. If you
lose signal in a snow storm, you can usually go out and lift up on the
lip of the dish, and the signal will usually come back. Not completely,
but much of it.
Also, as Eric said, this whole discussion has diverted attention from
the original discussion about the footprints being centered in the
middle of the US, and places like Florida being on the fringes.
Eric
> Also, as Eric said, this whole discussion has diverted attention from
> the original discussion about the footprints being centered in the
> middle of the US, and places like Florida being on the fringes.
Sanity prevails. <g>
Ken Johnson
"Eric" <knip...@homebody.com> wrote in message
news:3B4B6E79...@homebody.com...
> Bill Jones wrote:
>
> > Also, as Eric said, this whole discussion has diverted attention from
> > the original discussion about the footprints being centered in the
> > middle of the US, and places like Florida being on the fringes.
>
> Sanity prevails. <g>
Let's hope so, but I fear this useless drivel will last at least another
week.
Mike S
Snow in the dish, no signals. Depending on depth, Ku goes first, then
C.
Remove the snow, all is well.
Ergo snow is the problem.
It's pretty brute simple.
Ya'll are free to believe whatever else you choose.
Jack
wrote:
>Not from here. I've made my case:
>
>Snow in the dish, no signals. Depending on depth, Ku goes first, then
>C.
>Remove the snow, all is well.
>Ergo snow is the problem.
>
>It's pretty brute simple.
Simple answer, everyone should move to Florida, put up a 12 footer and
be happy like me... :)
James Bryant
James Bryant
The main discussion was size.
Size gives more gain.
Closer to the equator, the steeper the angle.
Farther from the equator the shallower the angle.
There is more chance of signal attenuation due to the amount and distance of
atmosphere and weather conditions regardless of the time of year, that have
to be negotiated by the signal.
As for the snow in the dish.
The main reason that snow has an affect on a microwave signal is the same
reason that light bends when it enters water. When enough snow and ice,
(especially ice, and most especially ice in layers),. build up thick enough,
(usually three or four inches in large dishes), it causes distortions in the
reflective pattern of the dish as well as absorbing part of the signal..
Reflect a sunbeam into a fish tank and notice what happens when passes
through the surface.
Microwaves behave like light. They do the same thing.
The Uplinker
http://theuplinker.com
R. Rikoski
James Bryant <theup...@earthlink.net> wrote:
> Size gives more gain.
Size gives more gain only if you can keep the reflector precisely
parabolic.
For perfectly smooth reflectors, a 12 foot dish gives 6 db more gain
than a 6 foot dish. (See ARRL Antenna Book p 278).
But if you can't keep the reflector surface smoother than +/- 1/3 inch,
you will lose the 6 db that you picked up in going to the 12 footer and
would have been just as well off with the six.
This doesn't consider the hassle of mounting the 12 footer; nor does it
consider that the 12 has to be aimed much more accurately to keep the
beam boresighted to the satellite; nor does it consider distortion of
the reflector surface due to snow; nor does it consider the extra cost
of the larger antenna; nor does it consider the extra cost of the
positioner.
Rick
Richard A. Rikoski, Ph.D, PE
JJ
usually most pronounced when the snow is near melting point
Felix Miata
> James Bryant <theup...@earthlink.net> wrote:
> > Size gives more gain.
> Size gives more gain only if you can keep the reflector precisely
> parabolic.
A properly engineered and constructed 12' dish won't be any less
accurate than a properly constructed smaller dish of same basic type.
> For perfectly smooth reflectors, a 12 foot dish gives 6 db more gain
> than a 6 foot dish. (See ARRL Antenna Book p 278).
> But if you can't keep the reflector surface smoother than +/- 1/3 inch,
> you will lose the 6 db that you picked up in going to the 12 footer and
> would have been just as well off with the six.
You may loose some, but the 6 Db assumes similar construction/accuracy.
Lower accuracy in the bigger dish may narrow the gap between the two,
but it would rarely be capable of eliminating it.
Cable companies don't spend lots of money installing big dishes at their
downlink sites just to make passersby gawk at the size.
> This doesn't consider the hassle of mounting the 12 footer; nor does it
> consider that the 12 has to be aimed much more accurately to keep the
> beam boresighted to the satellite
Gain is not the only component of signal quality/quantity improved by a
larger dish, but an off center 12' will generally provide a lot more
gain than a perfectly targeted 6'. A 50% efficient 12' reflector (40.77
Db gain) will produce far more than twice the gain of an 80% efficient
6' reflector (36.79 Db gain). For anyone who is easily satisfied by less
than the best, by all means don't get the largest possible dish.
--
For with much wisdom comes much sorrow; the more knowledge, the more
grief. Ecclesiates 2:8 NIV
Team OS/2 *** C/Ku since 1986
Felix Miata *** http://mrmazda.members.atlantic.net/
R. Rikoski
One last time, then I quit:
In article <3B4DBCEE...@atlantic.net>, Felix Miata
<ugaddabkidd...@atlantic.net> wrote:
> "R. Rikoski" wrote:
>
> > James Bryant <theup...@earthlink.net> wrote:
>
> > > Size gives more gain.
>
> > Size gives more gain only if you can keep the reflector precisely
> > parabolic.
>
> A properly engineered and constructed 12' dish won't be any less
> accurate than a properly constructed smaller dish of same basic type.
The key word here is "properly" Big dishes are harder to keep in
tolerance. And the tolerance is very tight.
I didn't make those figures up and it is not a matter of how I feel
about but rather it comes out of the antenna engineering books for
parabolas.
>
> > For perfectly smooth reflectors, a 12 foot dish gives 6 db more gain
> > than a 6 foot dish. (See ARRL Antenna Book p 278).
>
> > But if you can't keep the reflector surface smoother than +/- 1/3 inch,
> > you will lose the 6 db that you picked up in going to the 12 footer and
> > would have been just as well off with the six.
>
> You may loose some, but the 6 Db assumes similar construction/accuracy.
> Lower accuracy in the bigger dish may narrow the gap between the two,
> but it would rarely be capable of eliminating it.
You will lose all.
>
> Cable companies don't spend lots of money installing big dishes at their
> downlink sites just to make passersby gawk at the size.
Exactly. Cable companies need to spend "lots of money" buying solid,
not mesh dishes; and paying lots for engineering and installer time.
Big dishes are expensive to install and maintain.
For a hobbiest with a mesh-dish budget or with a solid dish of unknown
ancestry, 12 foot is about the tops.
Unless, his aim is to "make passerby gawk at the size."
>
> > This doesn't consider the hassle of mounting the 12 footer; nor does it
> > consider that the 12 has to be aimed much more accurately to keep the
> > beam boresighted to the satellite
>
> Gain is not the only component of signal quality/quantity improved by a
> larger dish, but an off center 12' will generally
No, a 12 that is off center by the same amount as a 6 might be off
center will miss the signal entirely even though the 6 is still getting
signal. The extra gain of the 12 comes at the cost (advantage in the
case of being able to distinguish 2 degree satellites) of reduced
beamwidth.
> gain than a perfectly targeted 6'. A 50% efficient 12' reflector (40.77
> Db gain) will produce far more than twice the gain of an 80% efficient
> 6' reflector (36.79 Db gain). For anyone who is easily satisfied by less
> than the best, by all means don't get the largest possible dish.
Make sure it is aligned properly, smooth and parabolic.
Felix Miata
of the continental US, where signals are higher than for most of the US.
He's had a lot of different equipment, including multiple smaller than
average reflectors. Signal strength is rarely his problem, but because
of the small dishes he uses, targeting two degree spaced satellites
often is.
"R. Rikoski" wrote:
> One last time, then I quit:
> Felix Miata wrote:
> > "R. Rikoski" wrote:
> > > James Bryant <theup...@earthlink.net> wrote:
> > > > Size gives more gain.
> > > Size gives more gain only if you can keep the reflector precisely
> > > parabolic.
> > A properly engineered and constructed 12' dish won't be any less
> > accurate than a properly constructed smaller dish of same basic type.
> The key word here is "properly" Big dishes are harder to keep in
What is the authority for this generalization?
> tolerance. And the tolerance is very tight.
Your perfectly accurate stamped 5' dish has theoretical efficiency of
100%, and gain of 36.18 Db. My sloppy old 12' dish with maybe .25"
average distortion is still pulling about 1.5 times the signal of your 5
footer, and mine isn't subject to objectionable C-band bleedover from
adjacent satellites like yours is.
> I didn't make those figures up and it is not a matter of how I feel
> about but rather it comes out of the antenna engineering books for
> parabolas.
What figures? Available dishes are what matter, not theoretical ones.
> > > For perfectly smooth reflectors, a 12 foot dish gives 6 db more gain
> > > than a 6 foot dish. (See ARRL Antenna Book p 278).
For those not aware, +3 Db means the same thing as twice as much, and
+10 Db means the same thing as ten times as much. +6 Db is a very big
difference.
> > > But if you can't keep the reflector surface smoother than +/- 1/3 inch,
> > > you will lose the 6 db that you picked up in going to the 12 footer and
> > > would have been just as well off with the six.
> > You may loose some, but the 6 Db assumes similar construction/accuracy.
> > Lower accuracy in the bigger dish may narrow the gap between the two,
> > but it would rarely be capable of eliminating it.
> You will lose all.
That presumes the smaller is perfect, which is unlikely. In the real
world, you will only see a narrowing of the gap, not its elimination.
And with the smaller's wide beamwidth, you retain the problem of pulling
signal interference off adjacent closely spaced satellites. As a
practical matter, few would be attempting to use a reflector with worse
than 1/3" average surface accuracy.
> > Cable companies don't spend lots of money installing big dishes at their
> > downlink sites just to make passersby gawk at the size.
> Exactly. Cable companies need to spend "lots of money" buying solid,
> not mesh dishes; and paying lots for engineering and installer time.
The real point is signal quality, not mesh vs. solid or at what price
quality.
> Big dishes are expensive to install and maintain.
My 12' certainly cost more to buy originally than a 10' would have.
Other than a 24" arm costs a bit more than the common 18" used on
smaller dishes, what maintenance cost? Same wiring, same feed, same
LNB's, and typically the same 10.5' long 3.5" diameter steel pole. My
1986 Saginaw still works.
> For a hobbiest with a mesh-dish budget or with a solid dish of unknown
> ancestry, 12 foot is about the tops.
Depends on location. Not everyone lives near Kansas. 12' should be
enough gain for most looking at sats ostensibly aimed near them, and
LOTS better than a 6'.
> Unless, his aim is to "make passerby gawk at the size."
> > > This doesn't consider the hassle of mounting the 12 footer; nor does it
> > > consider that the 12 has to be aimed much more accurately to keep the
> > > beam boresighted to the satellite
> > Gain is not the only component of signal quality/quantity improved by a
> > larger dish, but an off center 12' will generally
> No, a 12 that is off center by the same amount as a 6 might be off
> center will miss the signal entirely even though the 6 is still getting
There's never a reason for it to be off that much. A decent
mount/actuator combination will provide all the accuracy required to
ensure better signals than a 6' at all times.
> signal. The extra gain of the 12 comes at the cost (advantage in the
> case of being able to distinguish 2 degree satellites) of reduced
> beamwidth.
No small advantage is it to be able to reject adjacent signals entirely.
Each solar outage lasts many times longer on a wide beam antenna. Narrow
means you miss a commercial or three running plays. Wide means you miss
the commercial and several minutes before and after, or a turnover, 4
first downs, and a touchdown.
Picture quality depends on good signal to noise ratio. Signal from
adjacent sats is noise.
> > gain than a perfectly targeted 6'. A 50% efficient 12' reflector (40.77
> > Db gain) will produce far more than twice the gain of an 80% efficient
> > 6' reflector (36.79 Db gain). For anyone who is easily satisfied by less
> > than the best, by all means don't get the largest possible dish.
> Make sure it is aligned properly, smooth and parabolic.
There is no substitute for quality (accuracy, new and maintained). Given
comparable quality, there is no substitute for bigger (more gain AND
better signal to noise ratio).
ksi...@ticon.net
...
>Because _I_ really lust for bigger. If I could figure a way to manage
>it, I'd really like a 15 METER dish on an H-H or maybe even an AZ/EL
>mount with clear sky over the entire satellite arc!! Ever see a dish at
>a commercial uplink facility? Yup, that's it!! Other than that, your
>point is well taken. <G>
Somebody on IRC offered me a good deal on a 1000 footer. The only
problem is it's down in Puerto Rico, and I would have to go down
there, take it down, and find a way to ship it to the Midwest.
Interesting design though: the dish is fixed, and the feedhorn moves.
:-)
--
Milwaukeebonics lesson #12:
"Do you want your pants too to the cleaners sent?"
My REAL email address is ksinner
at ticon
dot net
rh...@megabits.net
D. Stussy
>On Mon, 09 Jul 2001 13:09:15 GMT, Mike S <NoS...@this.address.com> wrote:
>>Because _I_ really lust for bigger. If I could figure a way to manage
>>it, I'd really like a 15 METER dish on an H-H or maybe even an AZ/EL
>>mount with clear sky over the entire satellite arc!! Ever see a dish at
>>a commercial uplink facility? Yup, that's it!! Other than that, your
>>point is well taken. <G>
>
>Somebody on IRC offered me a good deal on a 1000 footer. The only
>problem is it's down in Puerto Rico, and I would have to go down
>there, take it down, and find a way to ship it to the Midwest.
>Interesting design though: the dish is fixed, and the feedhorn moves.
...And where is this dish again? Arecibo is only 500 feet. Did they build
another one next door?
rh...@megabits.net
They put "sideboards" on it.. <G>