C band reception problem

[[email protected]]

Hi,
I am from Pakistan.I can't receive c band channels on my satellite
dish from last 8 months.After a search i come to know that there is
Local Wireless (WIMAX) interruption in the signals .Please help me by
advising what i have to do to receive c band channels again as all
Pakistani channels are on C band.Please help.

 

[Jeff Liebermann]

[email protected] hath wroth:

I am from Pakistan.I can't receive c band channels on my satellite
dish from last 8 months.After a search i come to know that there is
Local Wireless (WIMAX) interruption in the signals .Please help me by
advising what i have to do to receive c band channels again as all
Pakistani channels are on C band.Please help.

Please read this page before beginning:
<http://www.satsig.net/itu/c-band-spectrum.htm>
Note that WiMax interference is possibly the result of your government
allocating BWA (broadband wireless access) service in parts the
satellite band (3.4 to 3.7GHz). They claim that interference would
not be a problem because Wimax operation travels parallel to the
ground, while your C-band dish is pointed upward. That will work, but
only if your dish does not "leak" or have holes that pickup signals
from directions other than the satellite. If you dish is made from
mesh and is bolted together, be sure to check if there are any gaps or
loose screws.

Next, you need to determine where the WiMax base station tower is
located. Then construct an obstruction between your dish and the
tower. This explains how it's done:
<http://www.satsig.net/satellite/reducing-interference-satellite-tv.htm>

Next, you might need additional filtering in front of your LNB:
<http://www.microwavefilter.com/tvrointerference.htm>
This goes between the polarization switch and the LNB. If the WiMax
service is operating in the C-band, this will probably do little.

 

[**THE-RFI-EMI-GUY**]

Back when C band was still occupied by common carrier microwave (in the
USA), it was common to see dishes installed with a sheet metal shroud
around the perimeter to block terrestrial signals from spilling into the
dish. I have also seen experiments where the edge of the shroud was cut
with an irregular pattern like a saw blade or petals of a flower in
order to create dispersion of any signals that still leaked by. Try
looking at dish antenna models with low side lobe patterns for an
idea. Perhaps you can fashion something to your existing dish.

Hi,
I am from Pakistan.I can't receive c band channels on my satellite
dish from last 8 months.After a search i come to know that there is
Local Wireless (WIMAX) interruption in the signals .Please help me by
advising what i have to do to receive c band channels again as all
Pakistani channels are on C band.Please help.

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©

"Treason doth never prosper: what's the reason?
For if it prosper, none dare call it treason."

"Follow The Money" ;-P

 

[Jeff Liebermann]

Back when C band was still occupied by common carrier microwave (in the
USA), it was common to see dishes installed with a sheet metal shroud
around the perimeter to block terrestrial signals from spilling into the
dish. I have also seen experiments where the edge of the shroud was cut
with an irregular pattern like a saw blade or petals of a flower in
order to create dispersion of any signals that still leaked by. Try
looking at dish antenna models with low side lobe patterns for an
idea. Perhaps you can fashion something to your existing dish.

The added dish skirt has a somewhat different purpose. It was to
eliminated direct pickup to the dish feed. Most C-Band dishes are
rather deep (small f/D ratio) causing the feed to be buried below the
edge of the dish. While the dish edges don't get much illumination,
there's also very little pickup from the sides. The dish shields the
feed horn.

However, a larger F/D ratio dish results in a more shallow dish, which
in turn results in the feed being located well above the edge of dish.
No shielding by the dish here. For optimium gain with a Chaparral
type feed, there will always be a small amount of overspray or
spillover.
<http://www.w1ghz.org/antbook/chap6-3.pdf>
That shows up as unwanted pickup at the edges of the dish. In order
to block that direct pickup, a skirt is added. The skirt is somewhat
effective with a deep dish, but next to useless with a more shallow
dish.

Therefore, if the WiMax interference is coming from a direction that
is in line with the feed to the edge of the dish, a skirt will help.
If it's the usual problem of gaps in the mesh reflector caused by
lousy construction or assembly, it won't do much.

 

[[email protected]]

The added dish skirt has a somewhat different purpose. It was to
eliminated direct pickup to the dish feed. MostC-Banddishes are
rather deep (small f/D ratio) causing the feed to be buried below the
edge of the dish. While the dish edges don't get much illumination,
there's also very little pickup from the sides. The dish shields the
feed horn.

However, a larger F/D ratio dish results in a more shallow dish, which
in turn results in the feed being located well above the edge of dish.
No shielding by the dish here. For optimium gain with a Chaparral
type feed, there will always be a small amount of overspray or
spillover.
<http://www.w1ghz.org/antbook/chap6-3.pdf>
That shows up as unwanted pickup at the edges of the dish. In order
to block that direct pickup, a skirt is added. The skirt is somewhat
effective with a deep dish, but next to useless with a more shallow
dish.

Therefore, if the WiMax interference is coming from a direction that
is in line with the feed to the edge of the dish, a skirt will help.
If it's the usual problem of gaps in the mesh reflector caused by
lousy construction or assembly, it won't do much.

--
Jeff Liebermann [email protected]
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Thanks to all members
I have now solid dish of 8 feet,before that i had mesh dish which i
replaced because of this problem but all in vain.Any how,i don't know
the shape of wimax tower but all mobile and different towers are on
right side of my dish and these are about 200m from my dish.I am
receiving all ku band channels easily but only problem is in c band.

 

[Jeff Liebermann]

[email protected] hath wroth:

I have now solid dish of 8 feet,before that i had mesh dish which i
replaced because of this problem but all in vain.Any how,i don't know
the shape of wimax tower but all mobile and different towers are on
right side of my dish and these are about 200m from my dish.I am
receiving all ku band channels easily but only problem is in c band.

The WiMax system operates near or in the C-band. Ku band should be
unaffected. Only C-band will be a problem.

200m is very close, especially if the towers are line of sight. Can
you see the towers from the dish? Can you move the dish?

Since you know the probable location of the WiMax tower, you should be
able to place an obstruction between your dish and the towers.
Anything that will absorb RF will work. Try aluminum foil, chicken
wire, wire mesh, sheet metal, or a wet blanket. Start by setting up a
temporary barrier between the LNB feed point and the probable sources
of interference. A small piece of aluminum foil on a wooden stick
will work for testing. Move it around the LNB to see which location
works best. If it goes away completely, then that's the direction the
interfrence is coming from.

If that is insufficient, try blocking the signal using a very large
piece of chicken wire or mesh that is larger than the dish diameter.
You're building an RF wall. This is not permanent and is only to see
if the interference can be blocked. If it's coming from multiple
directions, this is going to be difficult. Use this as a guide:
<http://www.satsig.net/itu/c-band-spectrum.htm>

It may also be possible to move your dish to a location that does not
look directly at the WiMax towers. If possible, locate the dish so
that a building or other large object is between your dish and the
cell towers.

If your dish is on a roof top, please consider moving the dish to
ground level to avoid terrestrial interference. Nearby buildings will
provide the necessary obstructions while hopefully, not blocking your
view of the sky.