Mikek,

on of the main problem of this newsgroup is that people write answers without
carefully reading the question.

Everyone tends to "convert" the question toward issues he is able to write
something about, Unfortunately those issues often have little to do with the
original question.

I am offering you my answer, which may be clear, so and.so, or hardly
understandable ... I do not know. But be sure that at least I paid maximum
efforts to appreciate your question (though my numbers do not always match
yours). I'll try to explain the issue in the easiest way I can, assumimng that
all components behave in an ideal manner.

Let us first resume your hypotheses:

- the antenna has an impedance equal to the SERIES of a 58-ohm resistance and a
capacitive reactance of -1,072 ohms which, at 1 MHz, corresponds to a 148.5-pF
capacitance
- your aim is to transform that complex impedance into a 1.5-Mohm
purely-resistive impedance, that would match that of your tank circuit.

That said, you must first appreciate that your antenna can be visualized in two
ways:

- as the SERIES of R=58ohm, C=148.5pF (as said above)
- or, by applying the series-to-parallel transformation formula, as the PARALLEL
of R=19,862ohm, C=148.1pF

These are just two fully equivalent ways of describing the same physical
antenna. You can freely use the one which suits you best. For our purposes let
us here visualize your antenna as the parallel of R=19,862ohm, C=148.1pF.

That said, assume for a moment that you are able to eliminate in some way (i'll
tell you after how) the 148.1-pF parallel capacitance. What would then remain is
a 19,862-ohm resistance, a value which unfortunately does not match the 1.5-Mohm
figure you wish to get.

So, how to get just 1.5Mohm instead?

Playing with the transformation formulas you would realize that, if the SERIES
representation of your antenna would hypothetically be R=58 ohm, C=54 pF
(instead of R=58 ohm, C=148.5 pF as it is in the reality), the corresponding
PARALLEL representation would then become R=1.5Mohm, C=53.9 pF. Just the
resistance value you wish to get!

But modifying the SERIES representation of your antenna according to your needs
is very easy: if you put an 85-pF capacitance in series with the antenna, its
total capacitance would change from C=148.1 pF to C=54pf. And the antenna SERIES
representation would then become R=58 ohm, C=54 pF, as you were aiming at.

Once you have put such 85-pF capacitance in series with your antenna, its
PARALLEL representation becomes R=1.5 MHohm, C=53.9 pF, as said earlier.

For removing the 53.9-pF residual parallel capacitance, just resonate it with a
470-uH parallel inductance. The trick is then done: what remains is just the
1.5-Mohm resistance you wanted to get!

In summary:
- put a 85-pF in series (i.e. in between your antenna and the tank circuit)
- put a 470uH inductance in parallel to the tank (in practice this just means to
increase the tank inductance by 470uH with respect to its nominal value).

73

Tony I0IX
Rome, Italy