[Elecraft] The use of a doublet

[Ron D'Eau Claire]

Tom, W0TOM wrote:

> May I make a radical suggestion? Use the internal K3
> antenna tuner! Now I know that most transceivers have
> internal tuners that will operate well only up to 3:1 swr.
> The K3 tuner is rated much higher than that. Indeed,
> I was very surprised how well it  works here in my station
> with my 135' foot dipole with 450 ohm ladder line and a
> balun.
> I highly recommend that one should consider the K3 tuner.
> It's a winner.

------------------------------

That's true of all the Elecraft tuners, AFAIK except the KX1's optional
internal ATU. 

Perhaps it speaks to Wayne's roots as a QRP enthusiast who loves operating
portable that the Elecraft tuners all have a very good matching range.

The KX1 has a slightly smaller range simply because he ran out of room to
squeeze any more toriods into the tiny space allotted to the tuner. Even so,
it'll load up most ad-hoc random wires and doublets. 

That said, the limitation on all tuners is what maximum currents (when
feeding very low impedance loads) and what maximum voltages(when feeding
high impedance loads) they can handle without parts failing. The smaller the
physical size of the tuner, the greater these limits, especially on
voltages. Anyone who has messed with a Tesla coil can attest to how high
voltage RF behaves. Nothing can replace lots of physical separation between
components, and that's not possible in a physically small tuner. 

A little attention to avoiding a "voltage loop" at the rig end of the feeder
will avoid that extreme condition.

Although baluns can be very unpredictable (and sometimes lossy) at extreme
impedances, many Hams have successfully used a 4:1 balun, like the Elecraft
BL2, to reduce the impedance at the rig to something the ATU can more easily
handle. That has the same effect as adding or subtracting feed line or
adjusting the length of the antenna, and it's obviously easier to do.  

Ron AC7AC