Trap and match

I have completed the 'L-match' network and re-checked the resonant frequency of the trap, 1821KHz; both are now ready to be installed with the new antenna, ( last posting ).
I made a very important improvement to the water-proofing of the original trap, ( posting dated 8th April 2010 ), by fitting end-caps. These are translucent polythene and originally the tops from curry paste jars. I was delighted to discover that they are a tight clip-on fit on the 90mm diameter former. I had carried out beforehand the traditional microwave-oven loss test on the material which passed. I will now look for similar jar tops for my other coax traps.
I must hurry to finish the antenna as a Canadian radio amateur is eager to contact me on the 160m band.

Antenna traps using coaxial cable

Traps are tuned circuits used in various types of antennas to allow multiband operation. They can be bought from commercial sources, or home-made with the advantage of low cost, ( almost nil ), and your choice of design frequency rather than the manufacturer's. Ever since I burnt out a bought trap, I have always made my own.
My preferred method is to use coaxial cable formed into a coil round plastic drain-pipe, and avoids using a high voltage capacitor as the self-capacitance of the cable tunes the coil to resonance. I have made lots in the past, several of which are currently incorporated into some of my antennas. For lowest loss traps, coax cable having the thickest inner conductor practicable should be chosen, unless the weight causes the antenna element to sag excessively.
The one I have just made is for a modification to improve my longwave antenna. It consists of 6mm diameter RG58C/U type coax cable round a 90mm diameter pipe. I easily tuned it to the precise frequency I wanted using a 'dip' oscillator, frequency meter and adjusting the spacing between the end turns of the coil. Then the turns were held in place by applying hot melt glue into the gaps.