I have a fairly modern calibrated Marconi signal generator I could use for a reference. How would I convert the output in mv or uv to equal an 11 nanowatt signal? Then I could do some real world testing!
Regards,Lee
Lee wrote: "I have a fairly modern calibrated Marconi signal generator I could use for a reference. How would I convert the output in mv or uv to equal an 11 nanowatt signal?"
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E = SQRT(P*R) where E = volts, P = watts and R = ohms. The output load expected by your signal generator probably is 50 ohms, but a 1/2-wave dipole is closer to 70 ohms. Using 60 ohms as a compromise and assuming reasonable VSWR, then the answer is about 830 µV.
So, depending on how accurate the attenuator and metering is in your sig gen, and how well you have constructed your 1/2-wave transmit dipole -- this setup should produce a peak, free-space field strength of approximately 250 µV/m when accurately measured 3 meters away.
The next thing to consider is that reflections of that radiated signal will affect the measured field, so for better accuracy the whole setup and testing should be done outside with at least 30 feet of clearance from everything else, and with the transmit dipole oriented vertically with the bottom of it at least 5 feet above the earth. Even the presence of the operator and the field strength meter system can distort the field, so the field strength meter might be placed on the earth under the receive antenna, and the meter reading read remotely (binoculars?). It would be wise to take measurements with the FSM antenna located 3 meters away in at least four compass directions (N/S/E/W).
There will still be plenty of room for uncertainties in doing this, but the result should be quite a bit better than a total guess.
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