Hello Petr, OH1FIG,
Petr> I made "loading coil" on diameter 80mm, length of coil about 100mm.
Petr> Turn by turn with litz wire. This litz has got outer diameter about
Petr> 1.2mm. There are about 7 layers or so.
Petr> There are two coils in series, one tapped and the second similar
Petr> as a vario.
This is probably the main cause for the phenomenon you experienced.
By putting two inductors in series, where the inductors have
significant coil capacity, you build up two coupled bandpass
filters.
Petr> When I tune to DCF39 on 139 kHz I experince two maxima!
This is exactly what the following arrangement would do:
use monospaced font to view
in---+---+ +---+
| | | |
C1 L1 <-M-> L2 C2
| | | |
out--+---+ +---+
L1, L2 and M are figurative inductors which
describe the actual circuit electrically.
Petr> No matter whether I tune switching taps or rotating with inner coil
Petr> of the vario.
The maxima should then change in frequency slightly.
Petr> I suspect that the coils have a very high capacity themselves
Petr> so ones I tune antenna capacity and the other time capacity of
Petr> the coil.
Yes obviously. To prevent 2 maxima in the operating
frequency range, you should minimize the coil's capacity.
You cannot prevent the coil capacity, hence always will
have a dual maximum behaviour from the coupled resonating
circuits. But you could minimize the coil's capacity
and force the dual maximum behaviour from the coupled resonating
circuits to occur OUTSIDE our operating frequency range.
Petr> I wonder how the loading coil will
Petr> behave with TX.
Should the operating frequency happen to be within the
two maxima, variations of antenna's capacity (wind)
and parameters of the circuit (resistance rises due to
heating under operation) could result in significant
phase variations and/or loading conditions for the
amplifier (most amps would not like such working conditions).
Petr> If this is true there should be only one maximum
Petr> measuring antenna current.
Yes. By minimizing the coil's capacity the unwanted
(but unavoidable) dual maximum effect could be forced
to occur (far enough) outside the working frequency range.
Petr> Anyway I take this as a proof that coils
Petr> doesn't do their job properly.
The coils do their job properly, the resultant circuit
however does not behave as expected / required.
Best 73
Gamal Soegiono (SWL)
50N01 / 08E27 / JO 40 fa
[email protected]
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