[Antennas] From transmission lines to tuners

[Wes (N7WS) and Linda]

At 05:09 AM 12/24/2002 EST, DJ5IL@aol.com wrote:
>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 ...

Exactly right.  I've offered a caveat about roller inductor Q elsewhere
(summary: it's low and gets lower as the inductance is reduced) but it's
just "theory" so it doesn't count in this discussion.

Thanks Karl for the clarity and real numbers rather than conjecture.