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How important is SWR?
- Thread starter Singularity35
- Start date
Anything under a 2:1 and performance will not be an issue. As for "melting the transceiver" I hope you were joking. Additional heat buildup in the finals is usually minimal. Extended operating times generate more heat under normal usage. Finals usually blow due to weird reactance voltages and phase angles stressing the components than due to actual heat.
There are three misunderstandings in this thread.
1. The reflected power form the transmission line, no mater what causes it, is reflected back up the line to the antenna.
Each time the power makes the trip up or down, the losses stack up from the normal line loses imposed each direction.
In an HF setup with a tuner, the tuner set to a match, the reflected power 'stops' at the tuner and never gets back to the radio. This is the effect of impedance transformation by the tuner and what it is used for.
2. The radio has a detection circuit to cut power above a predetermined ratio detection to protect the radio from the conditions that can exist in #3 below.
3. What happens in the radio is dependent on the reactance affecting the final stage. Capacitive or inductive in sign.
One causes the final to lower it's dynamic operating resistance and drawing more DC power/ higher heat dissipation.
The other sign causes an increase in dynamic resistance with a rise in 'RF' voltages. This risks burn out of the device junctions from voltages higher than it is made to work at.
At VHF and UHF we normally don't use a tuner, so match is important especially if the transmission line is long causing higher losses and the antenna is not at best match. These two items will eat your power from line loses and radio power fold back on top of it.
You can see these effects on a power supply with a current meter by noting the SWR J sign and see what each does to the current drawn by the radio.
Good luck.
1. The reflected power form the transmission line, no mater what causes it, is reflected back up the line to the antenna.
Each time the power makes the trip up or down, the losses stack up from the normal line loses imposed each direction.
In an HF setup with a tuner, the tuner set to a match, the reflected power 'stops' at the tuner and never gets back to the radio. This is the effect of impedance transformation by the tuner and what it is used for.
2. The radio has a detection circuit to cut power above a predetermined ratio detection to protect the radio from the conditions that can exist in #3 below.
3. What happens in the radio is dependent on the reactance affecting the final stage. Capacitive or inductive in sign.
One causes the final to lower it's dynamic operating resistance and drawing more DC power/ higher heat dissipation.
The other sign causes an increase in dynamic resistance with a rise in 'RF' voltages. This risks burn out of the device junctions from voltages higher than it is made to work at.
At VHF and UHF we normally don't use a tuner, so match is important especially if the transmission line is long causing higher losses and the antenna is not at best match. These two items will eat your power from line loses and radio power fold back on top of it.
You can see these effects on a power supply with a current meter by noting the SWR J sign and see what each does to the current drawn by the radio.
Good luck.
KM3F,
Wasting your time. You know and I know what you said was right but "what everyone knows" says you're wrong, so you are wrong. Right? I mean you gotta be, everybody has known that forever! Right?
Don't you just love it??
- 'Doc
Wasting your time. You know and I know what you said was right but "what everyone knows" says you're wrong, so you are wrong. Right? I mean you gotta be, everybody has known that forever! Right?
Don't you just love it??
- 'Doc
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