Thanks OG. Nice explanation. I run a vertical with a trans match at the base and I always knew that that reflective power was presumably going back up the radiator out of time with the original signal. I said to myself, "wouldn't that change the characteristics of the original signal?". But then I thought about the frequencies this is happening at and figured the period of the RF signal is so fast it would not have a noticeable effect on the intelligence coded on the RF signal. Your presentation here agrees with my original assumption. The period of say a 40M RF SSB signal is over 2000 times greater than the intelligence coded on it. Wondering at what point this would become noticable. For example, a super trans match that could resistive match a 4000 Ohm radiator. Would that put a noticeable effect on the coded intelligence? Thanks again.
Hi, Dave, I am to point out some of the errors in your presentation. 1.The diagram of the final stage of a bipolar transistor amplifier is simply wrong. We may forget (for a while)that it's a push-pull (for the suppression of the 2nd harmonics) stage with a 1:9 broadband ferrite transformer that couples with the output connector. You drew the Emitter of the final transistor grounded through a resistor and the RF is taken out across the resistor; it's very wrong. RF energy would be tapped out from the Collector of the final transistor that's grounded directly to "0" terminal of the power supply. 2. Reflections occur due to impedance mismatch at the end of the feeder. The impedance maybe above or below the characteristic impedance of the line. An SWR of 1.5, 2.0 and 3.0 represents impedance like 17,25 or 100 or 150 ohms respectively. A resonant antenna (in flat top configuration in free space (at a height of half lambda above ground) will have 73 +j42 ohm. An inverted V dipole will have around 50 ohm. 3. A short antenna is capacitive and a longer one is inductive at any given frequency. 4. The reflected energy from the feed point (due to mismatch) would return to the TX and would be re reflected towards the antenna; because it can't be dissipated in the reactive components. 5. If the impedance at the feed point is lower than the 50 ohm there is more current drawn and the final transistors would be melting away (thermal run away); if the impedance is higher than 50 ohm there's more voltage and if it's more than the final transistors can handle they will be blown away. 6. The ALC (automatic level control) function in the modern transceivers will kick in to action so that the power output will be reduced to half or even less to protect the finals. 7. The question asked is what happens to the RF energy once it leaves the TX. 8. Please make a video explaining the mechanism of RF energy getting dissipated in the form of Electromagnetic waves from the feed point. That will be more appropriated. Thanks. De VU2RZA
Please adjust the lighting so that the bulb is not reflected in the white board. Maybe just switch it off. Cameras these days can produce great images in low lighting situations.
Luckily the Electromagnetic Force is understandable ...... works at a distance. Not like the weak and strong forces that work within the nucleus of atoms.
