Ku-band: Minimum dish size?
Paul Urbanus
I currently have a 7.5 foot Orbitron mesh BUD with a C-band
feedhorn+LNB. I'm looking to get a C/Ku feedhorn+LNB.
Is my dish going to be big enough to get decent Ku-band reception?
If not, what is the minimum? I've read/been told that 10 feet is as
small as I should go.
As an aside, how strong is the signal from the Ku transponders on
satellite SBS-6. I watch my college team (Arkansas Razorbacks) play at a
local sports bar, and most of the backhaul feeds on on this bird.
However, we never are able to get a a completely clean feed - pretty
good, but not completely clean. Comments?
Thanks,
Paul
Gary Tait
<urbp...@hotmail.com> wrote:
>Hi,
>
>I currently have a 7.5 foot Orbitron mesh BUD with a C-band
>feedhorn+LNB. I'm looking to get a C/Ku feedhorn+LNB.
>
>Is my dish going to be big enough to get decent Ku-band reception?
>
>If not, what is the minimum? I've read/been told that 10 feet is as
>small as I should go.
That would be for digital C-band. For Ku on a big doesh, the size of
the dish isn't really important, it's accuracy, and size of the holes
is (if it isn't a mesh dish).
Pseud O. Nym
i...@speakeasy.net:
+++++++++++++++++++++++++++
How big is the dish at that sports bar?
Maybe they don't have it tweaked properly. If the backhaul is an analog
signal, it could be that the dish is not aimed properly or the
polarization is not set right or the receiver may not be tuned properly.
If it is a digital signal, it would have to be the receiver or the TV set
itself. With a digital signal a less-than-adequate signal would result in
a picture that either freezes or has large blocky artifacts in it ....
perhaps intermittently.
I would say that the minimum size for a Ku band dish would be about the
size of a DirecTV or Dish Network dish but those are strong digital
signals and they are subject to "rain fade" under extreme weather
conditions.
7.5 feet should be a very good size for KU-band but the mesh should be
smooth with small openings in it. I seem to remember that if a wooden
pencil fits loosely through the openings in the mesh, it is not a good Ku
dish.
I have recently been trying to set up a good dish for KU-DVB-digital
reception with the goal of replacing a 10' commercial spun aluminum dish.
The system that I bought included a 31" motorized dish. It seems to work
fine with all the signals except for the PBS feeds .... which happen to
be the ones that I am most interested in. The Montana PBS channel is
fine, but the 4 national PBS feeds are a bit on the weak side. I get a
lot of rain fade on them so I am still using my 10' dish for them. The
PBS feeds have AC3 dolby surround sound audio and if it is raining I get
some audio dropouts with the 31" dish. It may be the receiver that I am
using which is a Fortec Lifetime. I plan to try some other receivers to
see if they work better, but there are very few choices when it comes to
DVB receivers with AC3 audio capability.
I rarely check for KU-band analog signals, but there does seem to be
quite a few sports backhaul feeds when I do check so that may be what you
are interested in.
Good luck,
PON
BoBaFett
dish for Mpeg and my 1.2M and 7.5 Foot dish for Ku. analog/mpeg.
--
Richey
"Paul Urbanus" <urbp...@hotmail.com> wrote in message
news:T6CdnSuSEue...@speakeasy.net...
ric
> I currently have a 7.5 foot Orbitron mesh BUD with a C-band
> feedhorn+LNB. I'm looking to get a C/Ku feedhorn+LNB.
>
> Is my dish going to be big enough to get decent Ku-band reception?
A Ku dish can be much smaller than C-band. I've seen Ku dishes
3' and smaller perform quite nicely (depending on the satellite.)
Dish shape and alignment are much more critical on Ku, however.
As far as SBS6 goes, it is one of the lowest powered Ku birds, and has
a strange downlink frequency allotment. Refer to lyngsat.com for particulars.
georg...@excite.com
>Paul Urbanus wrote:
>
>A Ku dish can be much smaller than C-band. I've seen Ku dishes
>3' and smaller perform quite nicely (depending on the satellite.)
>Dish shape and alignment are much more critical on Ku, however.
They are only much more imporatant if you are using a C band dish to
get a Ku band signal. If you use a 3' dish for Ku the beamwidth goes
up.
dtheat ~ wavelength /dish radius for fixed wavelength the greater the
dish radius, the smaller the beamwidth, which makes Ku so hard to get
on a 10'dish
ric
> >A Ku dish can be much smaller than C-band. I've seen Ku dishes
> >3' and smaller perform quite nicely (depending on the satellite.)
> >Dish shape and alignment are much more critical on Ku, however.
>
> They are only much more imporatant if you are using a C band dish to
> get a Ku band signal. If you use a 3' dish for Ku the beamwidth goes
> up.
There is no such thing as a "C band dish". Dishes are merely reflectors.
Nit picks aside, if the shape and/or alignment is bad on a small dish
used for Ku only, gain will suffer and focal point will shift. As far
as beamwidth goes, sidelobes are as much or more of an issue on small
dishes. The Ku-band 3dB down beamwidth of a 3' dish is about 1.9 degrees.
This is more than wide enough to worry about dish shape and alignment,
especially with 2 degree spacing of satellites.
georg...@excite.com
>georg...@excite.com wrote:
>> They are only much more imporatant if you are using a C band dish to
>> get a Ku band signal. If you use a 3' dish for Ku the beamwidth goes
>> up.
>There is no such thing as a "C band dish". Dishes are merely reflectors.
I suppose there is no such thing as a uhf or vhf antena either, there
are only rigid arrays of cylindrical reflectors. I'm going to right
down to radio shack and order my next rigid array of cylindrical
reflectors for OTA video reception tonight. Do you think I might have
more luck if I asked for a VHF antenna or even, heaven forbid, a TV
antenna?
>Nit picks aside, if the shape and/or alignment is bad on a small dish
>used for Ku only, gain will suffer and focal point will shift.
And if the alignment is bad on a C band dish (Opps, sorry, I mean 10
foot reflector) the exact same thing happens.. The point is for fixed
dish size the angular deviation to the first null is a function of
wavelength. The shorter the wavelength, the smaller the deviation.
>As far
>as beamwidth goes, sidelobes are as much or more of an issue on small
>dishes. The Ku-band 3dB down beamwidth of a 3' dish is about 1.9 degrees.
>This is more than wide enough to worry about dish shape and alignment,
>especially with 2 degree spacing of satellites.
Trying to align a 3' dish to 2 degrees seems a little easier that
trying to align a 10' dish (Opps, sorry, I mean 10 foot reflector) to
~1/2 degree. to get a Ku signal.
I do not think we disagree on matter of fact, I just think we disagre
on your first imprecise statement "Dish shape and alignment are much
more critical on Ku". The more precise statement is that it depends on
the size of the dish.
But... feel free to be as imprecise as you like, and take umbrage and
make silly satements like "There is no such thing as a "C band dish".
Dishes are merely reflectors".
After all it's usenet ;)
ric
> I do not think we disagree on matter of fact, I just think we disagre
> on your first imprecise statement "Dish shape and alignment are much
> more critical on Ku". The more precise statement is that it depends on
> the size of the dish.
Dish shape and alignment are three times more critical on Ku, especially
if you want to avoid the side lobe and adjacent satellite interference
problems that a wide beamwidth and two degree spaced satellites provide.
Anybody that has been in the BUD business for 25 years will tell you how
important dish shape and alignment are for Ku reception, especially digital.
If you choose not to listen, that is your choice.