kl7aj
05-04-2007, 05:59 PM
Squint Flackwelder, NA9QXZ, has a problem. #(Besides his name, that is). #
Squint has a pair of really nice dipole traps....at least he THINKS they're nice. #They're hermetically sealed in opaque plastic. #Unfortunately, they're unlabeled. #He can only guess what band they're for.
However, he does have a nice grid dip oscillator. #He tries out several probe coils on his GDO, and finally finds a dip when he brings it near one of the traps....it's 14.2 MHz. #The other trap reads the same. #Cool, he says.#He can build a two band dipole, for #twenty meters and....and...
He realizes that he is still missing some information. #He can assume the trap was built for a 20/40 dipole, but it would be only a guess. #Even if he guessed right, he still doesn't know how long to make the ends on the outside of the traps. #He could take a stab at some "typical" trap dipole dimensions...but with the cost of copper, he really hates to do too much cutting and trying.
To really design this antenna, Squint knows he needs to know the L/C ratio of the trap just as much as he needs to know the resonant frequency!
Squint has a fairly well-stocked #supply of R.F. components, but not much in the way of test equipment.
With no more test gear than he has on hand, how can Squint determine the L/C ratio of the traps? #(No, he can't saw the thing apart!)
Squint has a pair of really nice dipole traps....at least he THINKS they're nice. #They're hermetically sealed in opaque plastic. #Unfortunately, they're unlabeled. #He can only guess what band they're for.
However, he does have a nice grid dip oscillator. #He tries out several probe coils on his GDO, and finally finds a dip when he brings it near one of the traps....it's 14.2 MHz. #The other trap reads the same. #Cool, he says.#He can build a two band dipole, for #twenty meters and....and...
He realizes that he is still missing some information. #He can assume the trap was built for a 20/40 dipole, but it would be only a guess. #Even if he guessed right, he still doesn't know how long to make the ends on the outside of the traps. #He could take a stab at some "typical" trap dipole dimensions...but with the cost of copper, he really hates to do too much cutting and trying.
To really design this antenna, Squint knows he needs to know the L/C ratio of the trap just as much as he needs to know the resonant frequency!
Squint has a fairly well-stocked #supply of R.F. components, but not much in the way of test equipment.
With no more test gear than he has on hand, how can Squint determine the L/C ratio of the traps? #(No, he can't saw the thing apart!)