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Do you mean in a cable or do you mean radio waves in the air? The only way to stop the latter is to make a box of metal or screen and go inside it and close the lid. This is not as strange as it seems. There are companies who make such boxes and there ar others that specialize in treating the walls, floor, and ceiling of building rooms to make them into large metal boxes.
there is no way to prevent radiation through the air with RLC circuits. You have to use bulk material to absorb the radiation. http://www.eccosorb.com/ sells such material. Or you have to reflect it with conductive planes that are either solid or contain wires that are closely spaced.
If you want to prevent the signal from going through a cable, use a band stop filter. www.nuhertz.com has programs to design such things. Some of their programs are simple and free, others are complex and will work for 20 days for free.
Give more information about your project. Is it in a school class on a certain type of technology?
You can absorb a small amount of energy with a receiving antenna connected to a resistor.
U can jam mobile phones by generating a RF wave with noise modulated in it. This RF wave frequency should be same as that of the mobile phone downlink frequency. I once repaired a GSM mobile phone jammer unit and it worked on the same concept. These units have a range of 100-150 feet max(for use in movie theatres concert halls, hotels,hospitals,....).
Any jammer above this range will be illegal.
According to what I have been told of the FCC rules, intentionally jamming communications is illegal at the federal level which carries much severe prison terms than crimes at the state or local level.
Do not press your luck of not getting caught. You may also be taken to court for a personal damage if you keep someone from phoing for medical help and they die or get worse.
If you need to block some old radio phone with analog control, then you need to know frequency combination of HangUp code. It can be dual tone package or single tone of 1-2 seconds message. For example, russian long way (30 - 60 km) radio telephone "Altay" is using tone of 2363 Hz for HangUp. I know story when someone has made autorepeater with HangUp TX to block phone radiochannel. It was sending HangUp tone for about 2 sec in every 1-3 minutes with near 20 W power.
Radio-control did not react at all. There are a lot of reasons for that:
They have no equipment to take bearing in mobile.
They have not enough staff to make control at all.
They have no wish to make it.
As I know they have no rx for frequencies more than 1 GHz... It could last forever without any doubt - I think that near 80 - 95 % of power radio telepfones in my country have not licences. Radio-inspection is very weak here. How do you think about illegal 10 W TV channel on 175 MHz that was made by some 20 year boy, it was working 24/7 for about a half of year in the center of capital? What was reaction? All have made antennas to receive it. As I remember I was viewing F1 races on this channel. He has terrible sound modulation... For 2 or 3 times inspectors have visited his home, but father was saying that boy is not at home at this moment, and even not stopped brodcasting - "Come next time, friends ...". As I remeber it was at 1994 when Ayrton Senna died.
That HangUp beacon was working for few weeks, firstly user was thinking that he has damage on his radiotelephone system, but after a while he has asked my friend to solve it and he has changed a channel of radiotelephone. That was at 1997 or 98.
I have made some proposal to organize private firm to clean air, but authorities do not wish to hear it - this mess is good for them... It is very simple to find location of radio-telephone base - you need to have some radio-station with control system to make short phone call from phone base to telephone number with CallerID.