[AMPS] Re: SWR, power and losses

["Dick Green".]

> Imagine the following setup:
> 
> Amplifier - SWR meter #1 - antenna tuner - SWR meter #2 - feedline -
antenna.
> 
> Suppose all of the inductors, capacitors, feedlines and antennas have no
> ohmic losses (i.e. they don't heat up).
> If the antenna has an SWR of 3:1, it reflects 50% of the power reaching
it.
> Adjust the antenna tuner until SWR meter #1 says the amplifier sees a
perfect
> match, and adjust drive to 1500 watts on meter 1.  This means meter 1
will
> show 1500 watts forward, and 0 watts reflected.
> 
> Then SWR meter #2 will show 3000 watts forward and 1500 watts reflected.
> Net power radiated from the antenna is 1500 watts, same as the amplifier
> produces. 

I agree that 1500 watts will be radiated, but the meter won't read twice
the power being delivered by the amp. Theory or no theory, that's not what
I've seen in actual practice. Just to make sure my memory isn't shot, I ran
down to the shack and set up a test. I used a transceiver with a built-in
SWR/power meter (same as meter #1), built-in antenna tuner, and an external
SWR/power meter (same as meter #2). The antenna and frequency were selected
to produce a SWR of 3:1, the antenna tuner was activated to produce a
match, and the transceiver was adjusted for 100 watts of output power. As
expected, meter #1 reported an SWR of 1:1 while meter #2 reported an SWR of
3:1. *Both* meter #1 and meter #2 reported exactly 100 watts forward power.
Finally, meter # 2 reported reflected power of 25 watts (Hmmm. I guess it
*should* be 50 watts -- perhaps my lousy GAP multiband vertical is losing
half of the reflected power as heat.)

In my opinion, my FCC output was 100 watts (ignoring resistive and feedline
losses, etc), not 75 watts.

73, Dick, WC1M



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