It is sometimes disturbing to have a AM radio in a countryside and not being able to get the reception clearly. It is simply because of the distance of the radio station and also the strength of the station. The only solution is to attach a powerful antenna to the receiving radio the uniqueness of the antenna lies in its simplicity and cost. The basic knowledge of making an antenna is there in the back end.
Generally, the frequency range of amplitude modulation in 560 to 1650 KHz in order to resonate the LC circuit that that is the antenna (2Ï€fL=1/(2Ï€f_c ))
4Ï€f^2 LC=1.Using this formula and using a 30- 450 pF gang condenser the handy inductance built on a 350ft long PVC pipe works quite well.
The inductance built around a PVC pipe is basically an air core inductor, the inductance of which is govern by the formula L=(R^2 N^2)/(9R+10l) where L is inductance in μH, R is coil radius in inches, l is coil length in inches and N is number of turns. The calculated inductance in tune with 33 pF- 330pF tuning capacitor should be around 250uH. Honestly with the proper geometrical calculation of winding a 3ft long PVC pipe an inductance value of 170uH is expected but in practice the inductance came out to be 213μH because of winding and error in winding spacing. The number of turn was around 500 and standard wire gauge of the wire 24. A secondary coil having 50 turns on the top of the primary was connected to the 4 turns of wire wound directly in the radio itself. His is to be noted that orientation should be such that the internal antenna of the radio should be co-axial with the external winding. Instead of this if you are allowed to open the radio set a few turns of the external antenna needs to be wound on the rod antenna of the radio. The best result is achieved when this tailored antenna is in perpendicular direction to the radio station and to be kept horizontal to the ground. The methodology of tuning the antenna is quite interesting. Firstly we need to select a very weak station of the AM band co that you hear sufficient amount of noise, at this point of time it is advisable to tune the gang condenser (antenna capacitor). Finally slight amount of physical adjustment of the rod maybe helpful. The electronic appliances, those have TRIACs , high voltage transformer, SMPs, high frequency devices may create electrical interferences and that is a concern, the antenna should be kept away from them.
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