| Notch filter made with coaxial cable. |
|
A simple and cheap HF notch filter could be made with a 'T' coaxial connector inserted in your antenna line with a 1/4 wave
length open line connected to the vertical part of the 'T'. The cable length in meters = 75 / Frequency_in_MHz x Cable_velocity_factor. |
Measurement: The cable going to the antenna and the cable going to the radio have been connected to the 'DUT' and 'DET' miniVNA Pro ports. The DL2SBA vna/J software used in 'transmission' mode display the following graph. Example for 40 meters band notch. The RG-58 cable length is: 75 / 7.080 x 0.66 = 6.99 meters |
Situation: You are located near an AM broadcasting station, transmitting on 967 KHz. You can make a notch filter with a length of coaxial cable. You will get an attenuation of 25 dB of the AM signal. The insertion loss on top band is only 0.2 dB. The cable length is: 75 / 0.967 x 0.66 = 51.18 meters |
Much better results can be achieved with RG-213 or other low loss coaxial cable for the stubs. |
.