Bob Furtaw wrote:
Hams can not design good Q circuits. I always hear them complaining on the
air. I hear "a lousy Q, a lousy Q" followed by their call signs. :-)
Love it!!
Actually, I measure Q by the following Method (for ferrite or iron
powder cores):
First, wind about 10 turns on the toroid. Then put a capacitor across it
- preferrably a 1% mica or similar. Now, connect to a signal generator
via a non-inductive resistor, put an oscilloscope (preferrably with a
X10 probe) across the parallel tuned circuit and find the resonant
frequency Fr. Add a smaller amount of capacitance across the circuit and
re-measure the Fr. Measure the signal generator voltage and the voltage
across the tuned circuit at resonance.
Now you have all the data necessary to calculate the inductance, stray
capacitance and Q. Vary the resistor so that the voltage drop across it
at resonance is about the same as the voltage across the tuned circuit
to maximise the measuement of Q.
If the Q is lower than expected, try a range of Fr by changing the
number of turns and/or the resonating capacitance.
How accurate is this? Good enough for my purposes
73 de Alan
VK2ADB