The orientation of the FCP relative to the L's horizontal wire doesn't
matter. It's folds are designed to self-cancel fields. This works both
ways. The induction from an L horizontal into the 5/16 FCP is more than
ten dB down from the horizontal's induction into 1/4 wave radials.
Smaller can be a killer for QRP. PORTABLE may need smaller, but QRP does
NOT. Particularly at QRP you need the least amount of loss possible
anywhere and everywhere. An extra bit of loss not perceptible at all on a
QRO signal, may drop a QRP signal into the noise and no copy.
That PARTICULAR toroid is chosen because:
a) The low mu and powdered iron means it will not saturate with QRO.
b) The loss is low enough with that material that it will run QRO
brick-on-key and stay cold (have checked).
c) The loss is low to support QRP
d) The larger size of the (low mu) toroid helps provide the high degree of
coupling needed between the windings.
e) The form factor provides enough winding space for 20 bifilar turns of
low loss #14 wire with teflon sleeving for QRO.
f) The residual inductance from the transformer is close to being the
conjugate for the FCP's reactance. That means that the two together are
close to self resonant on the low end of 80.
g) This in turn means that the simple use of FCP, isolation transformer and
"pruned-to-resonance" wire, delivers a wire length that is close to a
quarter wave, and with the total wire involved (9/16 wave outside the
transformer) the feed Z comes close to a convenient 50 ohms. A shorter
pruned-to-length wire means more current in the FCP, and more loss in the
ground.
Mess with the toroid choice and the winding turn count on the toroid, and
you screw up all that convenient convergence of advantages for the rock
bottom simple configuration. Pay the $14 bux for the toroid and deal with
it. That's cheaper than a family meal at McDonald's.
You need the 228 Al value of this toroid and the room to wind. You could
get similar Al of 250 with a T200-1, of number one material, but the inside
diameter goes down to 1.25 inches from 1.94, and now you can't wind with
teflon sleeved or insulated #14, and you have to use insulated #18. You
are now getting into loss, the evil enemy of QRP. But you DID save $7 on
the toroid :>).
I already saved you $26. I can for sure do the BEST job using a T400A-2
toroid made of the same # 2 powdered iron, that costs $40. Jerry Sevick
settled on this expensive toroid as the best core for a 160-10 voltage
balun for the output of a QRO tuner, one that actually delivered the same
performance on 160 as 10. You can find the details on that in his balun
book.
People are going try anything I guess, but I am telling them methods and
components that we have TESTED, made contest scores with for over a year,
and KNOW WORK, have low loss for QRP, and handle power. I will not be able
to vouch for or troubleshoot alternate methodology. Roll your own methods
and you're walking away from what we're familiar with. The first question
I am forced to ask is what components you used.
73, Guy.
On Fri, Dec 9, 2011 at 11:15 AM, Jim F. <j_fitton@yahoo.com> wrote:
> Great reflector !
>
> I am a new list member, condo dweller, Top Band lover, QRPer, and
> contester.
> And strangely enough these present a challenge for others and maximum
> enjoyment for me :-)
>
> 1. Is the FCP shown in the diagram in a line with the inverted L wire ?
>
> 2. Do you think a smaller T200-2 transformer would work (QRP levels) ?
>
> Profuse thanks,
>
> jim / W1FMR
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
>
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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