I was asked to develop a linear
amplifier for an RC transmitter (35MHz).
transmitter uses a simple telescopic antenna, and
now I will have to design the amplifier and adapt
it´s output to a 50ohm transmission line and antenna.
So far so good, but then, as I started to analyze
the problem, things started to complicate a little.
In order to adapt the amplifier´s input to the
transmitter´s output, I need to know the transmitter´s
output impedance components (resistive and reactive
The resistive part should be something
much lower then 50ohm, which is the typical impedance
of short whip antennas (antennas bellow resonance).
I also know that short whip antennas present
a natural capacitive reactance, and to counteract
this, the transmitter has an inductive reactance
part on it´s output to balance with the capacitive
reactance of the antenna.
This is called Conjugate
Matching and in order to adapt my amplifier´s input,
I also need to know the magnitude of this inductive
Now, my question is:
How do I
measure these values without using high priced equipment,
like network analyzers?
Are there any techniques
to do this, with an outside test setup made of variable
capacitors, inductors and resistors and then measuring
phase shifts, voltages and currents in some way
on this setup, with an oscilloscope, that will allow
us to calculate the resistive and reactive parts
of the transmitter´s output impedance?
tells me that this is possible, but how?
appreciate any help.