Topband: Transformer Question

[K9AY]

Ford

You started out OK...

You can cancel the reactance at either side of the transformer.  The 260
+j330 will be transformed to about 65 +j82.5, but not exactly, due to
stray inductance, and the capacitance between windings .

But the statement that 1000 pF is less lossy than 264 pF is not the case.
First, any typical capacitor you would use in this application will have
very
high Q and, therefore, very low loss.  Next, even if the 264 pF cap has
four times the resistive loss of the 1000 pF cap, it is operating in a 4x
higher impedance circuit. Its fraction of the total impedance is the same,
so
loss is the same despite the higher resistance.

I am curious about the reason for your question -- is this for TX or RX?
(The numbers you give seem to fit a receiving antenna.)

73, Gary
K9AY
-----------------------
> I need to know if there is a correct solution to transforming complex
> impedances.
>
> Assume a perfect 4:1 transformer at 1.83MHz.  A load with R+/-j of 260
+330j
> I am fairly certain that the R term just divides down to ~65ohms
> (260/4=65).  What happens with the j term?
>
> To tune out the 330 ohms, a 264pf series capacitor is in order.  If the
j
> term divides down to 82.5j, then a capacitor on the input side of 1000pf
is
> in order.  If I had to choose, the 1000pf is less lossy and would be
best
> placed on the input side of the transformer.  Right?  Or am I missing
> something...
>
> Thanks for the feedback in advance.
>
> Ford-N0FP
> ford@cmgate.com
>
>
>
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