Quote:
Originally Posted by dodgy-dxer
Two comments
The efficacy of a filter will depend upon WHERE the IMDs are being generated.
*IF* they are in your receiver(s) then filtering will help prevent front end IMD due to overloading
However the IMDs could be generated at the transmitter site and are being radiated in the band you want to listen to. Or as someone suggested somewhere else local to your receiver, the "rusty bolt" effect. These product will pass straight through the filter in your receiver
A quick look at the frequencies someone posted shows you are vulnerable to 5th and 7th order products
Secondly I would suggest you try, if you have space, a resonant dipole antenna for the band you are interested in rather than random or wide-band antennas
Good luck
Fred
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Thanks Fred. Great points.
For the fact that the filters are inserted between the antenna and receiver, I used to think that the problem was always in the antenna end. The antenna feeds with higher RF voltage than the receiver front end can cope, thus the cross modulation or over modulation occurs. The filters are to attenuate the voltage and feed with the refined RF to the receiver, I used to think.
The over loading in my receivers don't happen all the time, but sometimes usually in the evenings. Tonight, it happened again. I switched on the radio, and tuned to 4.7 Mhz, and there were these strong MW signals from 4.7 to all over to 5.2 Mhz. The antenna was a Chinese made MLA30 in the room. It was pointing to east and west. When it was moved around to point South and North, the MW breakthrough signals disappeared.