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WI MAX Kills C band reception - Dead!
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(4160 H 26479SR) Intelsat 5 on a 1.8mtr - 5150LO LNB 9.8CNR 71% quality Notice the ripping effect? Classic WiFi Interference. |
Wi MAX is an acronym for worldwide Interoperability for Microwave Access. Wi MAX is a telecommunications technology that provides for the wireless transmission of data using a variety of transmission modes, from point-to point links to full mobile cellular-type access.
Wi MAX can provide up to 70 Mb/sec symmetric broadband speeds without the need for cables. The technology is based on the IEEE 802.16 standard (also called 'Wireless MAN'). The name "Wi MAX" was created by the Wi MAX Forum, which was formed in June 2001 to promote the standard. The forum describes Wi MAX as "a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL".
In principle, Wi MAX can be deployed on practically any w i r e l e s s frequency band.
W o r l d w ide several countries including New Zealand have deployed Wi MAX in the
Extended C band (3.3 GHz to 3.8 GHz). The issue of interference between Wi MAX
and C-band satellite has been raging for the last couple of years.
Numerous technical studies, including one released by the Satellite
Users Interference Reduction Group (SUIRG), have confirmed the interference.
The Wi MAX Forum officially acknowledged the interference problem in early 2007.
"Long-term and detailed trials have shown that the operation of Wi MAX within the range of3.4 - 4.2 GHz C-band spectrum have repeatedly "wiped out" the ability of satellites to function across the entire band and caused the wide spread disruption of transmission signals
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The C band satellites down link frequencies affected are: Standard C-Band 3.800-4.200 GHz Extended ‘C’ Band 3.625-4.200 GHz, Super Extended C-Band 3.400-4.200 GHz
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Asia Pacific
Australia, China, Indonesia, India (3.3-3.4 GHz), Japan, Malaysia, New Zealand, Taiwan, China
3400-3430 and 3500-3530 to start Hong Kong & Singapore – band allocated to fixed satellite only It would appear that 3.4GHz spectrum. Has been dedicated to Wi Max These three bands cover 3.425GHz to 3.575GHz, seem to in use in major New Zealand Cities.
Use of the C-band for satellite communications is widespread throughout the world. It is
particularly vital for many countries, particularly southern Asia, because of its resilience in the presence of heavy rain. C-band earth stations are also used extensively in many developed countries’-band (“Standard C-Band” and “Extended C band”1) frequencies have been assigned for satellite downlinks since the industry was inaugurated more than 40 years ago. C-band services cover large areas. They facilitate intercontinental and global communications. The sensitivity of C band satellite receiving systems also means that they may be disrupted by mobile terrestrial use of frequencies in immediately adjacent bands.
Satellites affected in New Zealand are as follows:
Telstar 18 @138, Apstar 6 138, Vinasat1 @132, Asiasat4 @122, Palapa d1 @133,
Chinasat 6 @115.5, Asia sat 3 @105.5, Asia sat 5 @100.5
In certain places in Auckland where the Sky tower is in direct line of sight with IS5 this satellite can be also affected. The main problems seem to be occurring on the lower elevation satellites such as Chinasat and Asia sat 4.
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(4160 H 26479SR) Intelsat 5 on a 1.8mtr - 5150LO LNB 9.8CNR 71% quality The ripping effect can plainly be seen in the second row |
In some cases critical adjustment of the dish can eliminate this interference; however this does not always work. The test to determine if WI Fi, or WI max is affecting a specific installation is to move your dish onto another satellite.
Example if Asia sat 4 is being affected move your dish onto Chinasat 6 and if reception is normal then move it back and see what the result is. In some cases the interference just affects certain transponders. On china sat 6 the CCTV mux on 4116 is affected and all other transponders are ok. Asia sat 4 depending on the strength of the interference one or more of the transponders can be wiped out completely.
How do these transmissions affect C band operating satellite systems .At the C band earth stations antenna the terrestrial signal is much more powerful than the signal from the satellite. Typically, the power-flux density (pfd) of a C-band satellite signal at the C band dish antenna is about -122 dBW/m2 while the pfd of a 25 watt WI Max transmitter at a distance of 500 meters is around -50 dBW/m2. There is difference in power between the two signals of 72 dB. It is difficult to overcome this power difference either by shielding or filtering. At best, the FSS earth station antenna has a side lobe /back lobe discrimination of about 30 dB.
The interference caused into C band dish systems can be divided into three types1:
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(4160 H 26479SR) Intelsat 5 on a 1.8mtr - 5150LO LNB 9.8CNR 71% quality The severity of the interference can increase randomly.On the whole it happens more during the day, and often backs off in the evening. Unknown reason for this. |
1: Co-frequency Interference
If no shielding is available at the satellite antenna site, then interference can be caused as distances up to about 150 km.
2: Out-of-band Interference
With the existing out-of-band emission limits for offending transmitters, interference can be caused at distances up to 2 km. If additional filtering is implemented at the transmitter site, the distance may be shortened to about 0.5 km.
3: Receiver Saturation Problem
Signals from nearby equipment transmitting in the 3.4 – 3.6 GHz band will cause saturation of receivers with their LNB operating in the 3.7 – 4.2 GHz range. In this case saturation can be caused in satellite receivers located at a distance up to about 1.2 km. Off-the-shelf filters can reduce the interference level by about 10 dB in which case the interference can be caused at distances up to about 0.5 – 0.6 km.
It stands to reason that the best solution is to eliminate the effects of interference is to from entering the LNB in the first place. Commercial users such as TVNZ, TV3 would source custom made filters from such companies as the Micro Wave Filter Company.
This relies on a waveguide filter which is placed between the Feed horn and the input of the LNB, thus filtering out any interference before it reaches the LNB.
This solution is very costly but offers a high rate of success, offering up to 75dB of protection against incoming interference. Apart from the expense of such filters, they are only made to operate in one polarity, so a dual polarity system will require 2 filters, 2 LNB’s and an orthomode coupler or a separate Horizontal / Vertical input which the actual filter bolts onto before the LNB is bolted onto the filter. The LNB’s used with a waveguide filter should have a range of 3.7-4.2GHz rather than the more commonly encountered extended C band range of 3.4-4.2GHz.