[600MRG] Tuning my transmitter

[Rudy Severns]

Steve I should have mentioned using a non-inductive low value resistance to
sample the source current!  That's important.  Introducing inductance to the
source can lead to oscillations, especially in parallel MOSFETs. 

 

You can also use the Rds(on) of a MOSFET to determine the Ids current
waveform.  With a grounded source what you can do is sample and clip the
drain-source voltage, i.e. attached one end of a 10k resistor to the drain,
connect the other end of the resistor to a two or three forward biased
diodes in series to ground.  At the junction of the diodes you will have Vds
clipped down 1.5V or so depending on how many diodes you use.  This is fine
since Vds during conduction will only be a few hundred mV, depending on
current and Rds(on).  The voltage waveform at the junction of the resistor
and the diode string should give a reasonable picture of Ids during
conduction for tuning purposes.

 

GL and 73, Rudy N6LF