I recently became aware of this relatively new product, which appears to me to represent a significant advance in the technology of MW field-strength measurements. I looked over the data sheet at the Potomac Instruments Web site and nowhere did I see that Potomac claimed to have virtually eliminated sources of error, which I am aware are all too common in AM field-strength measurements. Yet, a gentleman I know, whom I respect highly and who has used one of these instruments, says that that is indeed what Potomac has accomplished. At first I was blown away, but further reflection made me wonder if some very significant possibilities for error don't still exist and can occur accidentally even if the operator has no intention of falsifying readings. I'm hoping that some of you who are experienced in AM field-strength measurements and FIMs can comment--even if you have not personally had the pleasure of using a 4100.
The 4100 has built-in GPS, so, at each measurement point, it takes readings of frequency, field strength, geographic coordinates, receiving-antenna azimuth with respect to the station being measured, date, and time, and places all of that data in its memory. The only thing the engineer who makes a series of measurements must do is take the instrument from place to place and listen to the audio to ensure that the correct station is being measured before committing the data to memory. Unless the engineer really wants to know the measured values, he doesn't even have to look at them.
It goes without saying (but I'll say it anyhow) that reradiation (and probably shielding) from nearby structures can
cause significant errors. (And the structures need not be cell towers or steel bridges; even the AC wiring in a nearby residence should be able to cause significant errors.)
And finally, there is the way the engineer holds the FIM. Isn't it true that the plane of the receiving loop antenna should lie along the radial being measured? In other words, shouldn't the plane of the FIM's antenna--if you could extend it--pass through the electrical center of the array being measured? Also, shouldn't the plane of the FIM's antenna be perpendicular to the earth? If you were to rotate the instrument 90 degrees in the vertical plane while keeping the horizontal axis of the loop parallel to the earth and pointed at the transmitting array's electrical center or, while holding the instrument vertical, if you were to rotate it 90 degrees in the horizontal plane, wouldn't it produce completely meaningless field-strength readings? And wouldn't there still be significant errors even if the rotation were a lot less than 90 degrees?
I believe that the 4100 has a built-in compass, but is that little device really sensitive enough to allow the operator to properly orient the built-in loop antenna with respect to the transmitting array being measured?
I await you thoughts and comments. Thanks.
The 4100 has built-in GPS, so, at each measurement point, it takes readings of frequency, field strength, geographic coordinates, receiving-antenna azimuth with respect to the station being measured, date, and time, and places all of that data in its memory. The only thing the engineer who makes a series of measurements must do is take the instrument from place to place and listen to the audio to ensure that the correct station is being measured before committing the data to memory. Unless the engineer really wants to know the measured values, he doesn't even have to look at them.
It goes without saying (but I'll say it anyhow) that reradiation (and probably shielding) from nearby structures can
cause significant errors. (And the structures need not be cell towers or steel bridges; even the AC wiring in a nearby residence should be able to cause significant errors.)
And finally, there is the way the engineer holds the FIM. Isn't it true that the plane of the receiving loop antenna should lie along the radial being measured? In other words, shouldn't the plane of the FIM's antenna--if you could extend it--pass through the electrical center of the array being measured? Also, shouldn't the plane of the FIM's antenna be perpendicular to the earth? If you were to rotate the instrument 90 degrees in the vertical plane while keeping the horizontal axis of the loop parallel to the earth and pointed at the transmitting array's electrical center or, while holding the instrument vertical, if you were to rotate it 90 degrees in the horizontal plane, wouldn't it produce completely meaningless field-strength readings? And wouldn't there still be significant errors even if the rotation were a lot less than 90 degrees?
I believe that the 4100 has a built-in compass, but is that little device really sensitive enough to allow the operator to properly orient the built-in loop antenna with respect to the transmitting array being measured?
I await you thoughts and comments. Thanks.
