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I've read suggestions for resistors ranging from 2.2 k ohms to 56 k ohms all the way up to 100 k ohms. The most recent information being the lowest value resistors. From the schematics I have seen, the resistors were placed in parralel between the antenna input and ground input. Or in the case of a two wire unbalanced input, between each wire and the case of the tuner which is grounded. It just depends on how much power you want to "waste" in the paralleled resistor. Think of it this way: IF you had a 50-ohm dipole antenna and you used a 50-ohm resistor across the antenna (and ignoring the effect of a 25-ohm load on your xmtr), half of your power go into the antenna proper and half would be dissipated in the resistor. That's probably too much, so try a 500-ohm resistor: now about 90% of your xmtr power goes into the antenna and 10% into the resistor. One more try: 5K-omn resistor: now about 99% goes into the antenna and 1% is wasted in the resistor. This leads to one of the "rules of thumb" from a beginning EE class oh- so- many years ago: the power loss from paralleling a 100*R-ohm resistor with an R-ohm resistor is essentially negligible. There is another GOOD effect of using any resistor across your feed line: a simple ohm-meter check from inside the shack can tell you if your feed line is intact! --Myron, W0PBV. -- Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge PhD EE (retired). "Barbershop" tenor. CDL(PTX). W0PBV. (785) 539-4448 NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol) |
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