can high swr cause higher power output?

[Lil'Yeshua]

If the antenna is tuned properly for 50 ohms and coax is not shorted and you have exactly 1/2 wave multiples then It might be a amp/radio mismatch. The '50 ohms' load the radio sees will not let current through the feed line to be excessive. But that's just my opinion

 

[Beetle]

Yes it CAN,

VSWR is just a simple meter.

It reads the SUM of forward and reflected power.

Here is an article explaining it.

The Effects of VSWR on Transmitted Power

No dispute there: the article talks about the POWER meter indicating higher because of combining forward and (re)reflected power. My answer to the OP addresses his claim that "...SWR swings up with audio." With a Monimatch type of combination Power and SWR meter, of course it does. The SWR, as I said, is not changing. The amount of forward power is changing, and the ratio between that and the reflected power is changing in step with it. The RATIO (standing wave RATIO) between the two values is remaining the same. With a cross-needle meter you can see this easily: the point at which the needles cross remains eerily stationary, even though both needles are jumping around.

 

[Lil'Yeshua]

No dispute there: the article talks about the POWER meter indicating higher because of combining forward and (re)reflected power. My answer to the OP addresses his claim that "...SWR swings up with audio." With a Monimatch type of combination Power and SWR meter, of course it does. The SWR, as I said, is not changing. The amount of forward power is changing, and the ratio between that and the reflected power is changing in step with it. The RATIO (standing wave RATIO) between the two values is remaining the same. With a cross-needle meter you can see this easily: the point at which the needles cross remains eerily stationary, even though both needles are jumping around.

That makes sense

 

[mr_fx]

higher reading YES... but higher power out, not really, it's lower

hear is an example...

I while back I built a dipole... half of it was just above the roof of the house (maybe 2 foot) the other half was about 15 feet above the deck in my back yard...

I showed about 55 watts or so out on the dipole I could barley be heard by a local... this was on an HR2510

then wen to a vertical, nice lower SWR, I was 10 over s9, but the meter only showed 30 watts

the the first one was the radio's power + a good potion of the radios power returning to the meter causing a really high, nearly impossible reading...

 

[W5LZ]

You have to think about what your measuring -is-. The combination of forward power and reflected power is equal to the total output of the transmitter. But then, the forward power minus the reflected power is what's being radiated. Can you see that?
- 'Doc

 

[bob85]

i hope he can't, that is far from how it works,

in a mismatched load situation as the op has here the meter reads the sum of the forward power plus re-reflected power,

the sum of the forward power plus re-reflected power can be higher than the transmitter power, you can see that on your meter as extra watts that you don't have from the transmitter,

reflected power is not lost power/power that is not radiated,

reflected power arriving back at the transmitter is re-reflected / summed with the forward power and sent back towards the load where some will be radiated and some reflected back towards the transmitter to be re-reflected,

the loss is coax loss, plus if you don't have a tuner at the transmitter your transmitter may see an impedance looking into the coax that it cannot deliver its full output power into.

 

[wavrider]

Here we go again, Walt Maxwells "Reflections".

Agreed BOB. Nice summation.

i hope he can't, that is far from how it works,

in a mismatched load situation as the op has here the meter reads the sum of the forward power plus re-reflected power,

the sum of the forward power plus re-reflected power can be higher than the transmitter power, you can see that on your meter as extra watts that you don't have from the transmitter,

reflected power is not lost power/power that is not radiated,

reflected power arriving back at the transmitter is re-reflected / summed with the forward power and sent back towards the load where some will be radiated and some reflected back towards the transmitter to be re-reflected,

the loss is coax loss, plus if you don't have a tuner at the transmitter your transmitter may see an impedance looking into the coax that it cannot deliver its full output power into.

 

[W5LZ]

 

[cjruger]

i hope he can't, that is far from how it works,

in a mismatched load situation as the op has here the meter reads the sum of the forward power plus re-reflected power,

the sum of the forward power plus re-reflected power can be higher than the transmitter power, you can see that on your meter as extra watts that you don't have from the transmitter,

reflected power is not lost power/power that is not radiated,

reflected power arriving back at the transmitter is re-reflected / summed with the forward power and sent back towards the load where some will be radiated and some reflected back towards the transmitter to be re-reflected,

the loss is coax loss, plus if you don't have a tuner at the transmitter your transmitter may see an impedance looking into the coax that it cannot deliver its full output power into.

This makes sense to me, it sounds like the problem lies in the antenna and getting it tuned properly

 

[W5LZ]

... exactly!

 

[Shockwave]

There has to be more to this than just saying the meter reads the sum of forward power and re-reflected power combined. I've seen just as many cases where a poorly matched load showed less power on the meter as I have seen it show more. Since the typical watt meter is just an RF volt meter, we should expect changes in impedance (up or down) to alter the reading the same way.

We know a both a 25 ohm load and a 100 ohm load equal a 2:1 VSWR but they will show entirely different readings on a watt meter. The 2:1 VSWR caused by the 25 ohm load will show significantly less power while the same 2:1 VSWR caused by a 100 ohm load will show significantly more than normal output power on the watt meter.

To make a long story short, the matching network on this 5/8 wave antenna probably has too little inductance between the main radiator and the tap point. This would not bring the impedance down low enough to match the 50 ohm cable and cause the power readings as well as the impedance to be higher than normal.

 

[bob85]

can you try that experiment with a transmitter that can be adjusted to give full output into whatever load impedance its seeing with the 25ohm & 100ohm (2:1 vswr) loads?

i would assume changing the load impedance while maintaining the same vswr changes the power the transmitter is able to provide into the line,

we often assume a transmitter designed for a 50ohm system will output its maximum power with a 50ohm load,
articles i have read prove that is not always true,

w2du and others tell us how we can have more forward power than the transmitter is capable of providing due to the summing of fwd & re-reflected waves,

from birds white paper
"For loads with a VSWR of 1.2 or less, the power dissipated in a load (Wl) is equivalent (with less than one percent error) to the forward power (Wf)

When appreciable power is reflected, as with an antenna, it is necessary to use the exact load power which is given by
wl = watts into load = wf - wr"

 

[wavrider]

op:op:op:

 

[Road Squawker]

Here we go again, Walt Maxwells "Reflections".

actually this apparent power increase on a meter is caused by a gross impedance mis-match.

this only applies IF there is a transmission line.

for systems w/o a transmission line, unless there is meter failure, indicated RF output power can never be greater than Xmitter output.

 

[wavrider]

actually this apparent power increase on a meter is caused by a gross impedance mis-match.

this only applies IF there is a transmission line.

for systems w/o a transmission line, unless there is meter failure, indicated RF output power can never be greater than Xmitter output.

What type of system transmits without a transmission line in the HF frequency?