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Antenna 'Traps' made from Coaxial Cable for a W3DZZ-like dipole My lowband DX-Antennas are only up in winter, so during summer I need something simple to at least make a few contacts on 80 and 40m. There are plenty of websites on which one can read and learn about the theory and construction of coax traps. As I didn't want to use a traditional parallel tank circuit made from lumped components, I decided using simple RG58 on a grey waterpipe. All losses are converted into heat. A loss of 1dB equals 20.6% of power. Running 1kW into a trap of 1.0dB loss means the trap heats up with 205W. Thats quite a lot! It's widely known that coax traps, if carefully constructed, reduce gain by about 1.6dB. How to calculate the power in linear terms? 1kW = 60dBm 60dBm - 1.6dB = 58.4dBm 105.84*0.001mW = 691W 1000W - 691W = 309W Just imagine boiling water (1cal = 4.184J), that means with 309W you can heat up 1ml of water by 74℃ within one second. Sounds amazing and scary at the same time. Tom, W8JI, investigated the loss of coax-traps and how to reduce it. It's common practice to tune the tank direclty to the frequency of interest, but that means that a lot of energy flows inside the resonant circuit. High current flow and finite Q result in high loss. That means that the losses increase the closer the operating frequency comes to the resonant frequency of the trap. Moving the trap-frequency slightly out of band reduces the losses significantly! I tuned my traps to 6.57MHz and slightly adapted the length of the corresponding dipole elements.
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