RE: T1 Antenna Considerations

Posted by Peter Zenker on Jan 05, 2006; 9:34am
URL: http://elecraft.85.s1.nabble.com/T1-Antenna-Considerations-tp385235p385249.html

Martin,
> As previously stated a halfwave end fed wire represents a
> very high impedance which is outside of the matching range of the T1.

I agree, the impedance hight depends on the capacitive load of the wire ends
against ground.

> I have found that a halfwave long wire works as long as it is
> fed against a raised counterpoise, ie. a wire lying over some
> nearby bushes.  In this case it works because the two wires
> are really an off center fed dipole with the radio in the middle.

But if you add any wire length to a Lambda/2 behind it´s feedpoint, the
impedance will still be high, you still are feeding at Lambda/2. On a given
length of long wire, the impedance is high every Lambda/2 length and low
every Lambda/4 length.

The only reason that the "use the nearby bushes" construct now can be tuned
by the T1 is that the impedance goes low because a part of the antenna is
lying "on the floor" now, giving high capacitance against ground which
allways lowers the impedance.

The worse thing is, that this part of the antenna now also is radiating into
ground ;-(

To make a t1 work with a halfwave, you may use a 15:1 / 9:1 Autotransformer
directly in the feedpoint.


A much better way has been published 1928 by the Austrian Radio Amateur
FUCHS. He added another half wave to the antenna, but this halve wave is not
a wire but formed by a parallel circuit.

________halfe wave wire_____________    coil
                                    |   /
                                    |   /
                             cap    =   /   _____
                                    |   /  /
                                    |   /  /______   50 Ohm

But I agree, this is not a solution for the T1

In Germany the FUCHS ATU is very common in the QRP Area since the German QRP
Club published an all band version.

72 de Peter, DL2Fi


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