Hi Ed,
I appreciate your kindness to share your experience with us about
constructing equivalent load: "I constructed a load bank consisting of 16
surface mount light bulb sockets, all wired in parallel. I just screw in an
array of 25/60/75/100 Watt rated lamps until I get the necessary current.
Sure, there's some unknown slight lead inductance and capacitance. But all
I want to do is draw a few amps DC"
I have two questions: (1)What is the impedance of your bulb array at 30
MHz? i.e., Zb=? @30 MHz. (2)What is the impedance of EUT at 30 MHz?
i.e., Ze=? @30 MHz
If we are not sure Zb=Ze @30 MHz, I am afraid, it's hard to say the
spectrum analyzer would receive the same RF emission at 30 MHz from noise
sources other than EUT, although the bulb array draws the same current at
60 Hz as EUT does. In other words, Zb=Ze @60 Hz is one thing, and Zb=Ze
@30 MHz would be another.
Let's see an example, assuming
Ze=Re+jXe, where Xe=Omega*Le, and Omega=2*Pi*F.
Re=20 Ohm, Xe=0.1 Ohm @60 Hz, Ze=20+j*0.1=>20 Ohm
Be=20 Ohm, Xe=50000 Ohm @30 MHz, Ze=>j*50000 Ohm
Conclusion: As far as the equivalent load is concerned, we can only pay
attention to the equivalence of resistance part of Zb and Ze @60 Hz. At 30
MHz, however, we should pay more attention to the equivalence of reactance
part of Ze and Zb instead.
Suggestion: We might need to check the equivalence of Zb and Ze @30 MHz by
using an Impedance Analyzer, e. g., HP4191A(?).
Thank you.
Please correct me.
Best Regards,
Barry Ma
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