Effect of high SWR on transmitter

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SUMMARY

The discussion centers on the impact of high Standing Wave Ratio (SWR) on ham radio transmitters. It is established that while many believe an SWR higher than 1.5:1 can damage final transistors, the reality is more nuanced. Reflected power from the antenna system does not return to the transmitter but can create standing waves that generate high voltages, which can indeed harm the transmitter's output stage. Therefore, high SWR can lead to potential damage if not managed properly.

PREREQUISITES
  • Understanding of Standing Wave Ratio (SWR) in RF systems
  • Knowledge of antenna systems and their components
  • Familiarity with transmitter output stages and transistor behavior
  • Basic principles of wave reflection and transmission lines
NEXT STEPS
  • Research the effects of SWR on RF transmission lines
  • Learn about antenna matching techniques to minimize SWR
  • Explore the design and protection of transmitter output stages
  • Investigate the use of SWR meters and their calibration
USEFUL FOR

Ham radio operators, RF engineers, and anyone involved in antenna design and transmitter maintenance will benefit from this discussion.

GhostLoveScore
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I've been reading about effect of high SWR in antenna system on my ham radio. A lot of people are talking something like - You can't have SWR higher than 1.5 to 1, it will blow final transistors of your transmitter.
I've read about it and it doesn't look to be true. In fact, it seems like power reflected from antenna system will not get back into the transmitter, but instead it will reflect back into the antenna system.

But on another side, if I create a short wave on a piece of rope with tied down another end, I will feel the wave when it reflects and gets back to my hand. And certainly, in transmission line, reflected wave comes back and forms standing wave when interacting with original wave. In that case it seems like reflected wave does have some effect.
So my question is, does the transmitter "feel" anything when EM wave reflects back from the antenna system? Can you fry your transmitter with high SWR in antenna system?
 
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GhostLoveScore said:
Can you fry your transmitter with high SWR in antenna system?
Yes.
Depending on the wavelength of the transmission and the length of the feedline to the antenna, standing waves can create high voltages with very low current in the output stage. Transistors do not like that.
 
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Most likely this can only be answered by an "old timer". I am making measurements on an uA709 op amp (metal can). I would like to calculate the frequency rolloff curves (I can measure them). I assume the compensation is via the miller effect. To do the calculations I would need to know the gain of the transistors and the effective resistance seen at the compensation terminals, not including the values I put there. Anyone know those values?

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