C- band interference 3

[saintjohn]

hi all,

i am working in direct to home company and i am part of a group that handles their TVROs for their program acquisition.

at the moment, we are experiencing some sort of an interference in one of our TVRO and the interfering signal is within the frequency of the signal that i am trying to receive. this means that i cannot use a c- band filter or notch filter to block the interference.

does any have any idea how i can get rid of the interference with out affecting the signal i am trying to receive? i heard that artificial shielding of the TVRO is one way of doing it. but i have no idea what that meant.

hope you guys out there can help me on this matter.

thanks and regards,
saintjohn

 

[VEBill]

Obviously - your C-band dish should provide more gain on the satellite than in any other direction. There will be sidelobes.

If the problem is as you state, then the only solution is to improve the ratio of signal to interference. Larger dish (more signal) and improved rejection of the interference (lower sidelobes).

First thing that I would do would be to track down the origin of the interference. This will confirm your assumptions, ensure that the problem is yours to solve, and it will determine if it is feasible or not.

You might need a spectrum analyser and a L-band receiver (IF = 950-1450 MHz ?) to figure out what the interference is.

I've seen C-band dishes with a pattern of semicircles around the outer edge to reduce edge diffraction and thereby improve the sidelobe performance.

It's common to move the dish to the other side of the building to block interference.

The main thing is to confirm your assumptions by finding the interference.

 

[saintjohn]

thanks for your suggestion VE1BLL. but do you have any idea how the artificial shielding works? my point of implementing the artificial shielding is that while we are looking for the source of interference, we can at least manage to receive the signal while temporarily blocking the interference through artificial shielding. some says that it includes putting up a fence (and grounding it to the ground) around the TVRO. hope you can help me on this matter again.

thanks and kind regards,
saintjohn

 

[VEBill]

Until you confirm the source of the interference, you wouldn't know on which side to install the metal fence (or wall). Also, it would be disappointing if the interference was still there even after the metal fence was installed.

The metal fence should be grounded for safety reasons (and probably will be anyway), but the grounding at C-band wavelengths is another matter and not required to reflect (block) a signal. Quarter wavelength at 4GHz is about 0.70".

Personally, I wouldn't lift a finger to solve the problem until I confirm the exact source.

 

[BrianR]

Use an analyser and see what other strong signals are near your frequency. You might be suffering 3rd order intermodulation.

 

[FriendlyBen]

Hi saintjohn, the apostle ))?

At the place I worked before, one of our customer, a local TV station was facing a kind of interference at 4 GHz, The downlink feed from the mother station was freezing from time to time. We finally found out that the parking lot light was defect and located just above the 4 GHz dish, the electric burst of that lamp goes high enough in frequency to jam the 4 GHz. We ask to move and repair the light, and everything came back to normal. I hope it may help !

Thanks !
FriendlyBen

 

[saintjohn]

hi all,

thanks to all of you guys! all your suggestion had been a big help to me. actually, we already found the source of the interference. it's coming from an airspan antenna, a wireless access system type of antenna, using the frequency of 3.7 to 3.8GHz.

once again, thank you for all your help!

regards,
saintjohn