B P L U S T V a . s .
Setting the antenna for the 10 MHz band is possible either in one turn or in two turns mode. We reccomend
testing of both these alternatives.
Due to short circuit of one turn and different values of L/C ratio at each band the quality Q of the antenna
circuit is not identical through all HF range. Testing of antenna demonstrated that it is acceptable penalty for
the possibility of simple tuning in whole range of HF frequencies with SWR near to 1:1. After correct tuning the
SWR ratio does not exceed value 1:1,1 see measured impedance characteristics and SWR on next figures.
Typical diagrams of the parameters of MLA-M antenna measured by means of antenna analyser AA-230PRO
are provided on pages 6-12.
Employment of MLA-M is very simple. For concrete band we switch proper mode by means of the jumpers
see figs. 4-6. After connecting the 50 Ohm coaxial cable from transceiver we try to set strongest received
signal or noise by setting both variable condensers. Then in TX regime with input max. 10 W we must find by
changing the ratio of capacitance of both condensers the very small value of SWR. Due to very high quality Q
of the antenna circuit, especially in mode with two turns (figs. 2 and 3) is the selectivity of the antenna so high
that correct tuning changes even under the influence of closeness of operators hand a few attempts and
some training will solve this possible problem.
Horizontal radiation diagramm of MLA oriented perpendicurarly towards earth see fig. 7. It shows two
rounded maxima and two sharp minima (¥ - shaped). The depth of minimum depends very strongly on
neighbour objects (instalation in wall), on the type of propagation, ionosphere etc. Diagram in horizontal
plane with loop paralel to earth is ilustrated on figs. 8, 8a. Possible inclination of the loop (figs. 9, 9a) enables
alternatively to obtain a few dB increase.
MLA-M
MLA-M
Operation
fig. 8
magnetic
field lines
15°
all signals attenuated >10 dB
fig. 7
fig. 7a
fig. 8a
fig. 9a
fig. 9
page 3
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