Passive filters?

[Mycroft]

It has been reported to me that a 2.8m C band antenna is experiencing S band radar interference despite the fact that radar filters are fitted. Is this possible and if so how come considering filters are passive? The report says that the system did not have interference for a few weeks after the filters were fitted but then it sparlked up?
Please be as technical as you like in your solution!

 

[IRstuff]

Did it have interference before installation of the filters? Assuming so, otherwise, what was the impetus to put them in at all?

Since the filters allegedly worked for a while and then stopped, one must ask whether they are still electrically connected, e.g., did some sort of corrosion or electrolytic effect occur at the contacts?

TTFN

 

[Mycroft]

Hi IRstuff

Thanks for a speedy reply. OK, the system is on a vessel and is positioned about 15M away from the S band radar. Naturally post installation the horizontal LNB kept being taken down by the radar so radar filters had to be fitted. This prevents the LNB's being fried but the video gets PRF interference which is really annoying the crew. The report says that the interference does not occur all the time and sometimes not for periods of a week? the system is one that causes the feed to rotate to maintain polarity during movement. Could it be that during certain angles of polarisation (due to ships sail paths) the interference occurs due to a bad fitting of the filter?
I am unable to get to the vessel to check it out and this scenario is a first for me so all help is much appreciated.
The filters are the type that have flange and gasket seals, they are not connected electrically?

Thanks for all your help

Mycroft

 

[IRstuff]

That's about extent of my knowledge, except that the radar filter is essentially a shunt that prevents the interference from getting to the LNB, so it needs to be both electrically and mechanically connected.

The electrical connection needs to be solid and ultra low resistance and low inductance. The mechanical aspect is that this is very much like liquid plumbing, so gaps in the mechanical seals could allow leakage.

TTFN