Wow. Obviously, it is in the antenna circuit. Could be a lightning arrestor, balun or a Standing Wave Ratio bridge for matching the antenna to the transmitter. Seems a bit small for AM Broadcast use, but maybe it is a low power transmitter?
This is something electropaw should be familiar with.
Well, it's got an RF ammeter, so it's obviously going to tell you something about the forward power of the antenna. I'm not sure what the device in the middle is, although it looks like a vacuum switch. I'm guessing when power is applied to the coil (small left hand terminal strip), that the RF relay switches the input and output around and reads forward and reflected power.
If it's only 8A full scale, that's not a ton of RF power. I^2 X 50= 3 kW (assuming a 50 ohm impedance).
The more I look at it, the more it looks like a DPDT RF relay that switches the meter polarity around.
Well, if they're running 1KW, then having a 3KW full scale seems reasonable. The RF relay/vacuum switch does something. I don't think the relay actually flips the meter polarity, but I think it does flip around some sort of bridge or RF sensing coil so you get forward and reflected power.
Using an RF ammeter is a pretty ancient way of measuring antenna power, although it does give you a very accurate representation of what's "going up the pipe." Our aircraft NDB transmitters still use RF ammeters. They need a constant strength signal regardless of antenna impedance, so the system is tuned to produce a specific antenna current. The actual power out of the transmitter may be varied, but we know the intensity of the radiated signal will remain the same.
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This is something electropaw should be familiar with.
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If it's only 8A full scale, that's not a ton of RF power. I^2 X 50= 3 kW (assuming a 50 ohm impedance).
The more I look at it, the more it looks like a DPDT RF relay that switches the meter polarity around.
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Using an RF ammeter is a pretty ancient way of measuring antenna power, although it does give you a very accurate representation of what's "going up the pipe." Our aircraft NDB transmitters still use RF ammeters. They need a constant strength signal regardless of antenna impedance, so the system is tuned to produce a specific antenna current. The actual power out of the transmitter may be varied, but we know the intensity of the radiated signal will remain the same.
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[IMG]http://i132.photobucket.com/albums/q17/acadieman2/flux-capacitor-real.jpg[/IMG]
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