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does the measured power actually leave the antenna?

 
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garyspang
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Joined: 11 Mar 2018
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Location: Clemson area, South Carolina

PostPosted: Sun Apr 15, 2018 8:39 pm    Post subject: does the measured power actually leave the antenna? Reply with quote

Power flow:
(Transmitter output) to (40ft of 50 ohm coax) to (very high resolution Auto-tuner) to (1:4 step-up transformer) to (32ft vertical antenna and 30ft motor-home chassis ground).
Measurement:
The applied frequency is 1.9 MHz.
At the transmitter output, a Bird watt-meter reads 105 Watts out and 2.5 Watt reflected (VSWR ~1.4). The loss is about 2.8%.
Without the Auto-tuner the transmitter protection folds back to 8 watts out and 8 watts are reflected (VSWR ~infinity). The loss is about 100%.
Question:
I know the tuner is presenting the antenna with its complex conjugate.
Does this also mean that 97.2% (less any tuner/transformer losses) of the applied power of 105 Watts is now actually leaving the antenna?

Thanks for helping me with this mystery.
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admin
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Joined: 03 Jan 2007
Posts: 201

PostPosted: Mon Apr 16, 2018 6:29 pm    Post subject: Reply with quote

If your antenna has VSWR of 1.4, then yes, 97.2% is delivered to the antenna.

How much is radiated depends on your antenna efficiency: http://www.antenna-theory.com/basics/efficiency.php

Many antennas have efficiencies above 90%, so of the power delivered to the antenna, if the design is good then most of the power is radiated.
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