The schematic of the Emtec ZM-1 tuner is below and shows you one
design of a tuner that has less loss than most others.
Since close coupling is important to keeping effeciency high the way you
wind the transformer T1 is important. Here is a picture of the actual Emtec
T1 coil. Notice that the output coil is wrapped on top of the input coil.
This may be very important.
The drawing below shows the effective resistances that exist on the XM-2
design. These resistors are labled Rs, R1, R2 and R3. By "effective" is
meant that you can't see or remove them. They change with Q which changes
with frequency and loading of T1.
The loss in the output of the transformer can be determined by simple
math. The power in the output will be Pout and the resistance total of the
circuit is Ra + Rs. The power used at the antenna will be Pa = Iout squared
times Ra. Iout = square-root (Pout/(Rs+Ra). So the result is:
Pa = (Pout/(Rs+Ra)) times Ra
As you can see if Rs is zero, then Pa = Pout. But when Rs is big then Pa
becomes smaller than Pout.
The primary circuits of the transformer can be done the same way. The
circuit with R1 and C2 will dissipate power exactly = to the current through
R1. The same with R3 and C2. If either of the circuits are resonant there
can be very high currents flowing through R1 and/or R2 which are loss.
R2 is in series with the 50 ohm input power source. So long as R2 is small
most of the input power will get to T1. But, like the output if R2 is large
then the input power reaching T1 will be
Pt1 = (Pin/(R2 + 50)) times 50.
The problem left is to measure the values of Rs, R1, R2 and R3. They are
related to Q by exactly
Q = X/R where Q has no unit, X and R are in ohms. Of course the
value of X in ohms is a direct function of frequency from X = 2 times pi
times frequency times the inductance in henry's for an inductor.
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