PART 2

NOTE: The theory of the proposed method becomes very simple in practice, when explained by a few schematics/illustrations, which I am not allowed to post at the moment, so I shall add them in future posts, when necessary permissions will be available.

Loop antenna equivalent circuit values in the HF frequency have been confirmed by MAMMANA antenna modelling performed by Phil, VK7JJ: note that the conductor diameter was set at 2.5 mm and we have a"real part" of Z which is the sum of radiation and of loss resistances.Calculated values are as follows:

Wavelength...........................80m.......... ......40m.............20m

Frequency fo, KHz..................3,550...............7,150.... ......14,150

Z, real part Ohm....................0.38................0.56... ..........1.1

Z, im part (inductive) Ohm......99...................207..............451

Inductance @ fo, uH...............4.4..................4.6......... ......5.1

Resonating capacitance, pF......453.................108...............25

The method outlined in the previous post is indeed theoretically possible, using data for polynomial filters with unequal terminations. In Reference 3, previous post, tables of lowpass element values are presented for filters accommodating not only in/out impedance ratios up to 1:10, but also prototypes matching a given impedance to open circuit (infinite Ohm) or to zero Ohm. This property is essential, because broadband loops made with thick conductors have real part impedances measurable in milliOhms, so the matching circuit must accommodate a termination approaching a short circuit.

In order to have a really low impedance loop, I calculated the parameters for a loop antenna with the same dimensions as the square loop specimen, but with much thicker conductor,bringing the diameter up to 15 mm, using the Magloop calculator spreadsheet Ver. 1.23. With this spreadsheet calculator we get the value of the radiation resistance separate from the loss resistance, so it is possible to optimize loop parameters before actually building the prototype. Increasing the diameter drastically reduces inductance and radiation resistance, while at the same time increasing potential bandwidth. Results are shown below:please note that resistances are now given in milliohms.

Wavelength.................................80m.... ............40m.............20m

Frequency fo, KHz........................3,550...............7,1 50..........14,150

Radiation resistance, mOhm..........0.5..................7.............. ...110

Loss resistance, mOhm.............:...34...................47...... .........66

Inductance @ fo, uH.....................2.8..................2.8... ............2.8

In the next post we shall look at a possible broadband matching circuit.

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