Z MATCH

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I made this Z match in the late seventies. It is made to the original design as published in the RSGB Handbook albeit with a slightly different layout. The box is partly made of wood and covered with aluminium foil on the inside. At one time an extra section of coil was added to the LF inductor to cover 160 metres. Then I discovered that the extra coil, which was made of very thin silver plated wire was getting hot and the unit had an efficiency of only about 15%. So I went back to using the extra shunt capacitor that is visible in the photograph. the unit served well right up till 1995 having been used with rigs FT7, FT101, and FT101ZD. Then I bought an FT840 and a peculiar problem reared its ugly head. When being used on 160 metres the rig would go into a very unstable oscillation at a frequency somewhere between 2 and 3 Mhz. I quizzed a couple of Yeasu engineers about the problem on their exhibition stand at one of the rallies. They were unable to shed any light on the problem, maintaining that as long as the rig was seeing 50 ohms it should be ok. When it was fed into a 50 ohm dummy load it was ok so I had no argument. So this Z match is suitable 80 to 10 but not 160 metres. Maximum power handling is 100 watts.