Real SWR?

[Giovanni Di Maria]

Hi everyone.
I have build a simple vertical antenna using 4NEC2.
After the simulations, the software gives me a SWR (50 ohm) of 3.55 and an efficiency of 92.91%
The report says, infact, that with a transmission power of 100 Watt, 7 Watt are losed and 93 Watt are radiated on air.

But looking for the official tables of SWR, i see that a ratio of 3.55 of SWR corresponds to about 68% of real transmitted Power by the antenna (and 32% losed).

What is the truth?
Is SWR of 4NEC2 different from the official tables of SWR?

Thank you very much.

Giovanni Di Maria

[Jeff]

Post by Giovanni Di Maria
Hi everyone.
I have build a simple vertical antenna using 4NEC2.
After the simulations, the software gives me a SWR (50 ohm) of 3.55 and an efficiency of 92.91%
The report says, infact, that with a transmission power of 100 Watt, 7 Watt are losed and 93 Watt are radiated on air.
But looking for the official tables of SWR, i see that a ratio of 3.55 of SWR corresponds to about 68% of real transmitted Power by the antenna (and 32% losed).
What is the truth?
Is SWR of 4NEC2 different from the official tables of SWR?
Thank you very much.
Giovanni Di Maria

NEC takes no account of SWR; the source that you specify forces that
voltage/current onto the antenna.

So if you attached a transmission lin eto your antenna with a tx at the
end you would see an additional 68% reflected from the antenna. The 3%
loss is in addition to what ever power reaches the antenna due to poor SWR.

Regards
Jeff

[Ralph Mowery]

Post by Giovanni Di Maria
Hi everyone.
I have build a simple vertical antenna using 4NEC2.
After the simulations, the software gives me a SWR (50 ohm) of 3.55 and an efficiency of 92.91%
The report says, infact, that with a transmission power of 100 Watt, 7 Watt are losed and 93 Watt are radiated on air.
But looking for the official tables of SWR, i see that a ratio of 3.55 of SWR corresponds to about 68% of real transmitted Power by the antenna (and 32% losed).
What is the truth?
Is SWR of 4NEC2 different from the official tables of SWR?

That table of SWR is the most misunderstood thing I have ever seen
printed for antennas.

That chart is for additional loss in the feedline. That is if you have
a very short feedline and for all practical measurments no loss you get
100% of the power going to the antenna. Then if you have a longer feed
line that has some loss, you have to add to that loss the aditional loss
in that SWR table.

I am not going to look up the chart,so this is just an example. Say
your feed line has 3 db of loss. You loose half your power is the SWR
is 1:1. If 3:1 then you have to add about 30% more loss. If 5:1, you
may have to add 50% more loss. That is why open wire can operate with a
very high SWR, it has very little loss. Where coax has a higher loss to
start with and the more SWR the faster the loss goes up.

[Giovanni Di Maria]

Ok.
Thank you very much Ralph.
I have understood
Giovanni