C-Band Downlink Interference 1

[brutus]

East coast C-Band downlink earth terminals have been experiencing periodic interference. The origin is unknown, possibly AWACS. Bandpass Filters have been intstalled between the recieve port of the feed and the LNB however, interference is still finding its way into the system. Has anyone out there identified the source of this interference of which I speak? If so what steps have you taken to eleviate it?

 

[etpineda]

Do you have a spectrum analyzer? This is important for us to identify the type of interference you are experiencing.

 

[brutus]

Spectrum analyzers have been used to identify the interferrence. The issue at hand is whether or not anyone experiencing this interference has had success in pin pointing the source and in the process alleviating it all together.

 

[Lionel1]

Gi guys:
I live in Miami, very close to the sea. And I has been living with interference for the past 2 years but being a big procastinator I leave that job for " tomorrow" and never try to fix the situation.

Finally after 2 years I decided to spend a weekend doing something that could work, and this is what I did with mix results:

I surrounded my C band antenna ( 10 feet) with mesh wire ( the one used for Screen doors, Storage bins and Small animal pets using 23 gauge) and I bougth this from my local Home Depot store and I attenuated in some grade this interference that is coming from all places ( all satellites are affected) and al Digital channels ( MPEG and Digicipher).

I don't have that problem in KU band. Only in C band.

I have Spectrum Analyzers ( 2 diferent units) but I don't try this step because I tough that with the mesh I could get rid of the interference and I was wrong.

After testing Saturday I reach a point where the interference was eliminated at least 70% but again Sunday night started in the same usual patern ( I get the interference every 10 seconds measured with a Chronometer).

My antenna now is " surounded" in the edge( al around the main ring where the antenna mesh is attached) by 24 inches high chicken wire covering all the external ring and the interference still there.....Not to strong like before..but still bothering me.

The only satelites where I have less problems are the Atlantic ones after Panamsat 1. NSS 806 is the one where the interference is smaller but when I come west....interference is all over again..not with the strenght before installing the mesh but still there.

Any Ideas?


Lionel Remigio
lremigio@commsearch.com

 

[brutus]

As far as I can tell the interference problem still exists at C-Band. However, we have been integrating a bandpass filter into our receive terminals. This component has offered some relief. The manufacturer is Microwave Filter Company and part number is 7892D. It cost approx. $550.00.
It's primary mission is to eliminate out of band radar & altimeter interference.

 

[Lionel1]

Brutus:

I ordered one of these filters today.
Your experience with the 7892 D is really good? And what means the letter D? There are many models for the 7892?

I have lots of people ( customers) in Latin American countries with the same interference problems and this filter can be a great siolution.

It works for you or you ? No more interference or less?

Thanks

Lionel

 

[brutus]

The letter "D" probably designates the passband of the filter. The performance of the filter appears to be above average.

 

[etpineda]

Is it possible to locate an uplink / downlink system near a transmitter tower of a UHF TV station? Will your uplink be affected or it is only the downlink side?

 

[brutus]

What frequency band will your earth terminal be utilizing?

 

[etpineda]

Actually the system is already working but we find it very hard to lock on downlink side, we're operating on the C-band. At the same time our bandwidth is only 3 MHz.

 

[brutus]

Do you have any filtering on the downlink? I.E. transmit reject filter typically installed on the receive port of the feed.

 

[etpineda]

No we don't have. The antenna size is 3.7m. for this system. In another downlink, we have 1.8m.; here we can easily received the signal unlike the latter set-up i mention. What do you think seems the problem? Is it RF interference due to proximity to TV tower. The antenna is almost 700 ft. above the ground, the uplink set-up is at ground level. Hope you imagine our set-up.

 

[brutus]

What type of low noise amplifier do you have integrated on the receive port of the feed? I.E. LNA or LNB.

 

[etpineda]

We're using LNB with 15 K noise figure. Hope this is quiet enough to have a lock on our signal. I'm not sure with its gain value.

 

[brutus]

Is your C-Band earth terminal receive only or do you uplink from it? If you are transmitting from your C-Band terminal you must install a transmit reject filter on the receive port of the feed. The LNB is a broadband amplifier and the transmit signal will make its way into the receive system in the form of noise. Typically the port to port isolation on most feeds is 30 dB. which is not sufficient enough to prevent the broadband noise from entering your recieve system. Hence, the need for filtering.

 

[etpineda]

Thanks we'll try it.

 

[PSUEE]

hi: your 10 second period c-band interference is
caused by the awacs patrols along the us coast.
the microwave filter part mentioned in some of
your posts, is the correct solution. if the plane
is extreeeeemly close to you. some of the radar
pulse might get through. the 10 sec. period is
the rotation period of the radome on the awacs
plane. this radar was never intended to be used
towards US soil for extended periods of time.

God Bless America !

 

[doug123]

I put a filter on and now my signal is great. In addition to the filter, I also purchased a new LNB with an input frequency of 3.7 - 4.2GHz (#140230-1 from Patriot Antenna). My old LNB was 3.4 - 4.2. Evidentally the radar interference was coming in between 3.4 - 3.6. Now my signal is better than ever.