Hello everyone.
I install the receving antenna for my receiver on the same tower that have broadcast-FM antenna . The broadcast-FM transmitter operate around 15 kiloWatts and the distance between those antenna are not so far (
Dear Watchara Amasiri ,
I will not repeat the answer that you need to either a very sharp band pass filter.
But such filter will be expensive. May be one of the solutions is to use a notch filter built in a form of trap shunting the output of the antenna or the bandpass filter. Normal this trap is built by a series resonant circuit shunting the existing filter.
The other solution is to make the polarization of your antenna perpendicular to the the polarization of the FM broadcast.
Best wishes
The answer: Yes.
On what band does your receiver operate? Its front-end is almost certainly being saturated. You will need a band filter between the antenna and receiver that blocks the 88-108MHz FM band that provides sufficient attenuation to prevent overloading the receiver front end (70dB or more of rejection should be sufficient).
Thank you very much.
My receiver operate around 136 - 174 MHz that assigned to the public safety service in my area.
I will try to use band stop filter
and will the share the result here.
Watchara, what you need is a sharp filter called "FM trap." I actually had to use one such filter, because I was using a big yagi, with an RF amp in the downlead, for FM radio and for TV. I had to put an FM trap in line with the lead to the TV set.
Pretty much the same frequencies as you are mentioning here. You should be able to find an FM trap, with F type coax connectors on both ends.
https://www.amazon.com/Broadcast-FM-Block-Filter-88/dp/B01LE9LRPM
I'm not sure whether the receiver itself might need to be shielded. It depends how strong that FM signal is, in the room where the receiver is located.
Any high-power transmitter can cause poor reception to a nearby receiver. This is a problem called 'Blocking' and is caused by the unwanted transmission overloading the front-end of the affected receiver. A notch filter tuned to the unwanted transmitter is a 'trap' that will remove some of the unwanted signal. Notch filters are not perfect - the 'stop' region is narrow and the skirts are really wide. Instead of a notch you could use a multi-stage band-stop filter with a wider 'stop' region and narrower skirts, but before you spend too much time tying to design one you should look at other issues and solutions. Is the unwanted transmission getting picked up on the antenna, or the antenna feed, or is it coupled directly into the receiver? If you have a high-gain antenna - like Albert Manfredi's Yagi - could you re-site the antenna so that it picks up less of the unwanted transmission. If you feel like being really analytical you could resign the antenna so that it exhibits a 'null' at the unwanted transmitter frequency and pointing to the unwanted transmitter.
Dear Watchara Amasiri ,
I will not repeat the answer that you need to either a very sharp band pass filter.
But such filter will be expensive. May be one of the solutions is to use a notch filter built in a form of trap shunting the output of the antenna or the bandpass filter. Normal this trap is built by a series resonant circuit shunting the existing filter.
The other solution is to make the polarization of your antenna perpendicular to the the polarization of the FM broadcast.
Best wishes
Yes, and the interference is likely from the transmitter directly or other EMI from related equipment and cables. The receiver is below the transmitter so there are cables running past the receiver on the way to the transmitter.
You need what is called co-site interference cancellation circuit.. This blocking is done because of mutual coupling between the two antennas and the received signal by your receiver exceeds the rejection level of the receiver filter.. That what is happened.. Try to search how to eliminte the cosite interference.. Or try to far the two antennas away from each others
Watchara Amasiri a 7th order elliptic high pass filter should work in your case. This can be readily constructed using high quality inductors and capacitors inside of a shielding enclosure.
Filter calculation from https://rf-tools.com/lc-filter/
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