Re: Antenna tuner
James Daldry W4JED
Take a low voltage transformer, connect a couple wires to the low
voltage winding, and while holding the wire ends, connect a common
1.5 volt battery between the wires. When you disconnect the wires
you will drop them, because the collapse of the magnetic field in
the coil will generate a voltage spike several hundred volts in
magnitude. Now, try it again with a 100 ohm resistor across the
winding. No spike. Now - makes no difference if the switch is a
relay controlled by a microcontroller or a manual knob switching
the inductance - it's a switch, a voltage, and an inductance.
Add a 3 db 50 ohm pad to the input of the tuner when tuning. The tuner will still receive 2+ watts to play with, and the resistors will greatly reduce the voltage spikes.
On 7/13/22 17:50, james jones wrote:
Blew my QDX finals using an ATU-100 set up for QRP. Bad mismatch on 40 but ATU found tuning solution. Power in to tuner was shown as 6.8 watts. Power into to 50 ohm load had been 4.5 watts. Apparently the QDX saw the mismatch before the solution was attained.