what type meter I had same prob with RadioShack meter it went really stupid on me so went to dosy aint had no prob yet and swr is reflective power meaning high swr puts power back in youre radio that's why it burns finals
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can high swr cause higher power output?
- Thread starter cjruger
- Start date
This subject is pretty deep if one looks at all the parts in play.
Here is another way of looking at it.
1. The meter does read the sum of the 'phase difference' between the forward power and the reflected power depending on the 'sign' +/-. It can't get away from it.
2. The antenna is not a match at the frequency being tested so sets up the condition the meter is forced to read.
3. As proof positive, use the same meter looking at the result into a 50 ohm dummy load and you will see the radio's true power.
4. Put a tuner in line after the meter and watch the power meter as you intentionally mis match the line both above and below the optimum 1 to 1 match. The power will read higher in one direction and lower in the other proving what the mismatch does to the meter reading.
5. Go one step farther and put a amp meter in the 12 volt line to the radio and do step 4 again. You will see the radio current consumption go up with one mismatch and down with the other proving the mismatch is reflected right into the final stage of the radio.
This change has at least two effects. A. it can increase the final heat dissipation causing destruction or B it can increase the RF voltage at the device junction above it's rating and destroy the junction.
Lastly the reflected power causing these change in the final stage also change dynamic impedance of the output stage.
So the bottom line is keep the SWR at 3 to 1 or less at any point in the operating band to keep the radio safe, keep the radio from folding power back, reduce feedline losses and have 'some' accuracy in power measurements.
Amplifiers are subject to the same effects in their output stage.
There is no basic difference between the final amplifier in a radio and an outboard amplifier except power level.
Good luck.
Here is another way of looking at it.
1. The meter does read the sum of the 'phase difference' between the forward power and the reflected power depending on the 'sign' +/-. It can't get away from it.
2. The antenna is not a match at the frequency being tested so sets up the condition the meter is forced to read.
3. As proof positive, use the same meter looking at the result into a 50 ohm dummy load and you will see the radio's true power.
4. Put a tuner in line after the meter and watch the power meter as you intentionally mis match the line both above and below the optimum 1 to 1 match. The power will read higher in one direction and lower in the other proving what the mismatch does to the meter reading.
5. Go one step farther and put a amp meter in the 12 volt line to the radio and do step 4 again. You will see the radio current consumption go up with one mismatch and down with the other proving the mismatch is reflected right into the final stage of the radio.
This change has at least two effects. A. it can increase the final heat dissipation causing destruction or B it can increase the RF voltage at the device junction above it's rating and destroy the junction.
Lastly the reflected power causing these change in the final stage also change dynamic impedance of the output stage.
So the bottom line is keep the SWR at 3 to 1 or less at any point in the operating band to keep the radio safe, keep the radio from folding power back, reduce feedline losses and have 'some' accuracy in power measurements.
Amplifiers are subject to the same effects in their output stage.
There is no basic difference between the final amplifier in a radio and an outboard amplifier except power level.
Good luck.
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nice try,... where did I limit my comment to HF?
but, since you asked,...... how about a random (or even a non random) length end fed antenna, worked against ground, connected directly to the rig?
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RatsoW8
Supporting Member, W9WDX ARC Member - WD8T
It won't do that but it may draw the smoke out of the finals. We've probably all seen this happen. I'm no engineer but I'd say the high swr is causing the meter to show faulty readings due to the current being reflected back into the meter. Just a guess but on the details but I bet the theory is close.
so what?, I guess a "gross mismatch" can only happen on HF then?
I notice you never replied about the end fed antenna w/o a transmission line:tongue: