Quote:
Originally Posted by Mr. Ham
Antenna tuners do not tune the antenna to resonance, they just trick the radio into thinking that the antenna they are feeding into is resonant.
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Almost true. They trick the radio into thinking the antenna isn't reflecting power back down the feedline to the radio. But even a perfectly resonant antenna can reflect power back down the feedline. For example, a two-conductor folded dipole,
perfectly resonant, will have an impedance of about 300Ω and a true SWR of about 6:1 when fed by a 50Ω feedline.
Quote:
Originally Posted by Mr. Ham
The transmit power is converted into heat, which is adsorbed by the tuner and the coax...
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Almost perfect nonsense. That is not what a tuner does. Also I think you meant "absorbed" since "adsorbed" makes no sense here.
What a tuner
does do is re-reflect that reflected power back up toward the antenna.
For example, suppose the antenna reflects 50% of the power back down the feedline, and also suppose for a moment that the feedline is lossless. Let's use a 100 watt transmitter and a perfectly adjusted (and lossless) tuner.
The transmitter sends 100 watts up the feedline, and the antenna radiates 50 watts and reflects the other 50 watts back down toward the tuner. The tuner re-reflects
the whole 50 watts back to the antenna, which radiates 25 watts of it and sends the rest back down. The tuner reflects
this 25 watts up again, and so forth. Eventually, the whole original 100 watts gets radiated. An RF wattmeter in the feedline would show 200 watts going up the feedline, and 100 coming back. This wattmeter would be telling the truth.
But if the feedline has any losses, the original 100 watts goes up once, with losses; half of what's left goes back down, gets reflected by the tuner, and goes back up -- three trips through the feedline, with losses each way -- and what's left after that goes up, down, up, down, up -- five trips -- and so on, with losses each time -- so the total loss can be a large fraction of the 50 watts that originally got reflected by the antenna. That's why a lossy feedline gets so much worse wth increasing SWR. Much of the original power makes multiple lossy trips up and down.
All of the losses occur in the feedline when the tuner does its job, and the transmitter sees no reflected power at all, and thinks the SWR is 1:1.
Clear as mud, right?