Hi Al,
Perhaps I did not state very clearly what I meant to say, however your
writing seems to confirm what I meant to say. What I meant to say is
that given a single configuration of L and C in an L network, and by
configuration I mean where the C is and where the L is with respect to
the source and load, and which one is shunting and which one is in
series, there is only one set of values that gives a solution. If you
move the parts around in different configurations, there will be
different solutions. Have I got this right?
DE N6KB
Alfred Lorona wrote:
> Any complex source impedance can be matched to any complex load impedance by
> two L network configurations. One will be a low pass (series L and shunt C)
> while the other will be a high pass configuration (series C and shunt L) when
> connected from source to load.
>
> Some source/load values will result in 4 possible configurations. It depends
> on the following two relationships between source and load impedances.
>
> The real part of the load, when the load is in the equivalent series form,
> must be less than 50 ohms, which is the usual source impedance.
> Simultaneously, with the load expressed in the equivalent parallel form, the
> real part must be larger than 50 ohms.
>
> An easiest way to find all of this out is to download the free L matching
> software 'LC Match' from RadioCom Corp which is easily found in the Google
> search thingie.
>
> For examples of all of the above, when matching a load of, say, 500 +j200
> ohms to 50 ohms at 14 mHZ, the two possible networks are:
>
> 1. series 185 nh, shunt 7 pf and which is a low pass network.
>
> 2. series 7 pf, shunt 231 nh and which is a high pass network.
>
> If the load impedance when in series equivalent form is, say, 15 +j30, notice
> that the 15 ohms real part is lower than the 50 ohm source. And notice that
> it is larger than 50, it is 75, when the load is in the parallel equivalent
> form. Therefore we would expect to see four possible configurations. And,
> sure enough, these are:
>
> 1. series 402 nh, shunt 410 pf.
>
> 2. series 322 pf, shunt 196 pf.
>
> 3. shunt 347 pf, series 1604 pf.
>
> 4. shunt 372 nh, series 215 pf.
>
> In the first example, the coil of 185 nh would probably be preferable to the
> larger coil of 231 nh for lowest tuner loss. Actually there's not much
> difference in this case.
>
> In the second example, things are pretty much even. Note however, that two of
> the possibilities require only two capacitors and no coils in the tuner.
> Unfortunately, the capacitor values appear prohibitively high and therefore
> difficult to come by. It's a toss up between solutions 1 and 4.
>
> I am not certain but I believe that all popular antenna analyzer instruments
> yield measurements in the series form but don't take my word for it. At any
> rate the LC Match program requires load input in the series form.
>
> As simple as an L C network appears, there are a few additional interesting
> subtleties but I didn't want to complicate the issue too much. If the load
> impedance is given as a parallel equivalent form, always transform to the
> series form to check for the possibility of four networks. Actually, the best
> thing to do is use EZNEC as the antenna modeling software, ARRL's TLW
> Transmission line software and RadioCom's LC match software. These will give
> you a comprehensive picture of your antenna system. Too bad there isn't ONE
> program that combines all three elements and none that I know about that
> calculates tuner losses; L, PI, T and others. What about that, you software
> writers out there?
>
> 73, AL
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>
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