Timeline for Why does an RF Amplifier fail when the SWR is high?
Current License: CC BY-SA 4.0
10 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Oct 13 at 19:23 | comment | added | Ryuji AB1WX | In my experience of experimenting with power amplifiers, designing, building and breaking many, the failure is most often and directly/instantly due to the greater voltage swing and greater collector/drain current, not increased heat dissipation. Of course, running a higher junction temperature decreases the reliability and eventually leads to failure. | |
| Aug 30, 2019 at 1:56 | comment | added | Andrew | @hobbs the fact that transistors have semi-conductors in them is not the reason why a final transistor might absorb reflected power ! where did you get that idea from ?? | |
| Aug 24, 2019 at 23:54 | comment | added | Scott Earle♦ | Not at all - it’s just a design constraint. Look at how ‘fragile’ semiconductor linear amplifiers are, compared to tube amps. The technology is improving, to the point where there are commercially viable semiconductor amps now available at more reasonable cost, but it’s still cheaper to buy a tube amp. Both technologies have advantages and disadvantages. A semiconductor amp is more physically robust (tubes are more delicate, by their nature), for example. | |
| Aug 24, 2019 at 19:42 | comment | added | Phil Frost - W8II | So semiconductors inherently absorb power? Seems like that would make it difficult to build an efficient transmitter with semiconductors. | |
| Aug 24, 2019 at 15:56 | comment | added | hobbs - KC2G | @PhilFrost-W8II the antenna absorbs some, but antennas are made of conductors and transistors are made of semiconductors. | |
| Aug 21, 2019 at 15:50 | comment | added | Phil Frost - W8II | Why does the antenna get to reflect the power but the transistor has to absorb it? | |
| Aug 21, 2019 at 10:39 | comment | added | Andrew | then what stops the output signal produced by the RF output transistor from going back into the transistor in the same was as the reflected signal caused by a bad SWR ? | |
| Aug 21, 2019 at 7:09 | comment | added | Scott Earle♦ | The power has to be dissipated somewhere. It gets sent along the transmission line to the antenna, and some of it is reflected back. The transmission line will convert some of the power to heat, but the lion's share of it goes right back to the output stage and PA transistor | |
| Aug 21, 2019 at 5:41 | comment | added | Andrew | why does reflected power generate heat in the transistor ? | |
| Aug 21, 2019 at 3:03 | history | answered | Scott Earle♦ | CC BY-SA 4.0 |