[Antennas] From transmission lines to tuners

2002年12月24日 05:09:08 EST

Hi Steve,
> Go to the palstar website (www.palstar.com) and look
> at their roller inductors. This is the key to all
> happiness! I use their biggest one, it's hardly more
> money than the lower power one.

be careful when you judge roller inductors: bigger does not always
mean better. The efficiency of a tuner is almost entirely determined
by the Quality factor Q of the inductor. And it might not be obvious
but it is a fact that roller inductors usually offer a quite low Q.
Paul from Palstar gave me the measured Q of their roller inductors
(unfortunately f/L were not specified): 90 (RI-28HP), 108 (RI-28C).
Obviously the smaller and cheaper one has a higher Q than the big
one which is made of flat stock and the big one simply accepts more
dissipated power. Paul wrote: "The pinch roller is at ground so the
dissapation is in the remaining coil that is not shunted to ground. The
ceramic roller col can take about 100 watts dissapation and I believe
the ribbon coil version might take 250 300 watts dissapation This is
why we provide a fan cooling system for the coil in the event someone
runs rtty through the tuner at 2500 watts". Thanks Paul for your info !
By the way: I also asked Henry Radio about the Q of their two rollers
(18uH/28uH "flat stock") and got the the following answer: "I'm sorry
but we don't have that information. Ted Shannon HENRY RADIO ..."
I can't believe it: Henry Radio has absolutely no idea about the Q
of their super duper high-priced roller inductors - Ridiculous !
Believe it or not: though the 48-position switched inductor gimmick
of a Vectronics VC300DLP atu is an example of a really miserable
tapped inductor, it has a higher Q at 3.5 MHz than the big Palstar
roller: I measured 124 at 9uH on 3.5MHz. And an Amidon T200-2
with 25 turns of #18 wire offers 8uH inductance at a Q of approx.
370 (!!!) at 3.5 MHz. So if you really want to build extremely efficient
tuners, use tapped inductors wound on a pile of several big iron
powder (mix 2) toroids ...
73
Karl, DJ5IL
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