what is your vswr at the antenna?

[The DB]

SWR and TRANSMITTERS - What is SWR all about? Making Sense of SWR Readings

Look at the chart and se the difference between 1:1 and 5:1 vswr on the receive end.

I was going to let your arguments go, but are you really proposing that anyone here in their right mind would run a radio at a 5:1 SWR at the radio end of the feedline? If not I ask why you bothered to post that as an example of what you were referring to?

Before I even to bother to read through this link I see errors right off the bat, namely the "% OF POWER LOSS" and "OUTPUT TO ANTENNA" sections of the chart. This information as it is posted directly contradicts what was posted in the other link you posted a few minutes before this one. I direct your attention to your own link, namely "The Real SWR Page" link to disprove the chart link that I am responding to. If you want further information on the subject find a freely available .pdf file called "Another Look at Reflections" by M. Walter Maxwell, which is basically the first six chapters of the book "Reflections Transmission Lines and Antennas" which was used as a source for the information on that page.

Long story short, just becuase power has been reflected does not mean it has been lost, and aside from the effects of attenuation on the feedline, all of said reflected power will be rereflected and sent back towards the antenna. This rerelfected power is not only not lost, but constructively adds to the signal that is on its way to the antenna. This has the effect of throwing off both of the columns in the chart. With such glaring errors right off the bat I now have to decide if the rest of the page is worth reading...


The DB

 

[The DB]

Actually waverider, I did read through the page... A few quotes that are worthy of attention...

When you add to this fact what is actually going on AT THE ANTENNA after the signal goes thru that feedline, you may be horrified!
That perfect 1:1 reading at the transmitter may translate to a horrible reading where it really counts...
at the antenna!

Learn More about SWR
(You may learn that higher swr can be better!)

Perhaps I have to re-evaluate, most of the things they mention line up perfectly with my understanding of the theory, now if they only re-worded that chart...


The DB

 

[wavrider]

I agree DB on the chart and the differences in the two articles.

Also it takes 5 cycles for the reflected power to be inverted 180 deg and be in phase with the transmitted signal from the antenna coupler.

The 5:1 VSWR is just a number I pulled from the chart to show how little loss of transmitted signal there is in a sever mis match at the antenna.

With that said here are a few examples of sever mis match antennas at the feed point yet they have great gain and good efficiency

Double extended Zep, Lazy H.

Even the yagi has a low impedance at the feed point and either has to have some sort of matching network.

The common 1/4wl ground plane. With radials at a 90 degree not a 45 degree angle is 98% efficient yet has a vswr of 1.4:1.

Lower the angle of the radials to 45 degrees and the vswr goes to 1:1 but efficiency drops slightly.

It is my understanding that a 20% decrease in efficiency is equivalent to a 1DB loss in gain. I may be wrong.

I am also not posting an arguement, just stating there is more to an antenna system than the antenna vswr at the antenna.

The quote you referred to if you would have copied and pasted the rest of it refers to feedline loss and the fact that the vswr meter can be fooled by high loss feedline, or long runs of feedline. So what is happening at the antenna may not be a true resemblance of what the vswr meter is showing at the transmitter.

 

[bob85]

waverider have another look at that link you posted,
in the example he uses you have 180degrees of phase shift at the antenna and the tuner,
the 180degree out of phase reflected wave from the antenna is re-reflected at the tuner 180degrees to bring it back in phase with the forward wave on every trip.

 

[wavrider]

Yes thought that is what I posted?

Takes 5 cycles to accomplish that.

waverider have another look at that link you posted,
in the example he uses you have 180degrees of phase shift at the antenna and the tuner,
the 180degree out of phase reflected wave from the antenna is re-reflected at the tuner 180degrees to bring it back in phase with the forward wave on every trip.

 

[bob85]

no it does not take 5 cycles for the reflected current to be rereflected back in phase with the incident wave, read that article again.

 

[The DB]

Also it takes 5 cycles for the reflected power to be inverted 180 deg and be in phase with the transmitted signal from the antenna coupler.

Yes thought that is what I posted?

Takes 5 cycles to accomplish that.

no it does not take 5 cycles for the reflected current to be rereflected back in phase with the incident wave, read that article again.

I've been looking around and can't seem to find anything to confirm the 5 cycles for a reflection to happen.

I do have a link to an old AT&T video form the 50's that seems to disagree with that premise.

AT&T Archives : Similarities of Wave Behavior (Bonus Edition)

Take a look, it is a good visual demonstration of how waves, including standing waves work. There is no 5 cycle delay on the wave machine for a wave to be reflected, it seems to be instantaneous, which makes sense.


The DB

 

[bob85]

every hammy class tutor & physics teacher should have a wave machine

 

[wavrider]

Copy and paste from the article.

Thought it said 5 cycles.

That's a lot of information. What is the actual result ?
What's the Score?

Input Power - - - - - - - - - - - - - - - - - - - - - - - - - - - -100 W
Loss of power going up the Coax- - - - - - - - - - - - - 8.55 W
Power reaching the Antenna - - - - - - - - - - - - - - - 91.46 W
Power Radiated by the Antenna- - - - - - - - - - - - - 88.91 W
Reflected Power returned to the Coax- - - - - - - - - -2.54 W
Loss of Power going back down the Coax - - - - - - 0.217 W
Power that arrives at the Tuner - - - - - - - - - - - - - - 2.32 W
Radiated power eventually evens out to?- - - - - - - - - 91 W.
(after about 5 cycles)
This shows where the power is lost, and what is radiated. This is far too much information

 

[Robb]

Think it is great info.

Gives a whole new perspective for using the best grade of coax one can afford - IMO . . .

Not that losing 10-15w makes that much different to a receiving station. But for a couple of dollars more, you can know that you have bought coax that doesn't take something away. If you don't think so; then go ahead and buy/use that ultra-crummy Radio Shack/Tandy junk. Worst specs of any coax available; stuff is like using a dummy load if it is long enough! Doesn't take that much either - lol.

 

[bob85]

waverider,

what i think he means is the 2.32w watts of reflected power arriving at the tuner re-reflects from the tuner without loss starting its second round trip back up the lossy coax,

when it reaches the antenna some of that 2.32w minus the loss in the coax on the trip back to the antenna will be radiated and some reflected back towards the tuner through the lossy coax where it is re-reflected from the tuner again in ever decreasing circuits up and down the coax with 180degree phase shift at each reflection point until there is nothing left to add to the incident wave.

 

[Marconi]

...........My testing of the A99??? Hmm? You sure you have the right person here? I haven't owned an A99 since long before joining this forum. I do recall you and someone else having such a discussion though.

The DB

DB you're right, I looked back and found the member I should have addressed, when I referred to your handle. It was in fact Northern35s, that had promised me he was going to do some testing on an A99. He was going to see if scanning his VA1 showed any difference in results...when checking directly at the feed point vs. using a feed line.

Again sorry.

 

[The DB]

Copy and paste from the article.

Thought it said 5 cycles.

That's a lot of information. What is the actual result ?
What's the Score?

Input Power - - - - - - - - - - - - - - - - - - - - - - - - - - - -100 W
Loss of power going up the Coax- - - - - - - - - - - - - 8.55 W
Power reaching the Antenna - - - - - - - - - - - - - - - 91.46 W
Power Radiated by the Antenna- - - - - - - - - - - - - 88.91 W
Reflected Power returned to the Coax- - - - - - - - - -2.54 W
Loss of Power going back down the Coax - - - - - - 0.217 W
Power that arrives at the Tuner - - - - - - - - - - - - - - 2.32 W
Radiated power eventually evens out to?- - - - - - - - - 91 W.
(after about 5 cycles)
This shows where the power is lost, and what is radiated. This is far too much information

To much information? We clearly differ on that. This information is useful in the right hands for tuning purposes, or if you suspect an issue somewhere in the antenna system.

They missed something, power absorbed by but not transmitted at the antenna due to losses in the antenna itself...

The antenna has a 1.4:1 SWR at its feedpoint, so why do they need a tuner? No one on the far end will notice the difference if a tuner is present or not.

There is no 5 cycle delay on reflections as the above video I linked to demonstrates, the reflection happens immediately. I wonder if they are referring to something else, perhaps that is the delay as the signal travels back and forth on the feedline in this specific case? Aside from the loss characteristics I know nothing about the feedline, including length and velocity factor.


The DB

 

[The DB]

Think it is great info.

Gives a whole new perspective for using the best grade of coax one can afford - IMO . . .

Not that losing 10-15w makes that much different to a receiving station. But for a couple of dollars more, you can know that you have bought coax that doesn't take something away. If you don't think so; then go ahead and buy/use that ultra-crummy Radio Shack/Tandy junk. Worst specs of any coax available; stuff is like using a dummy load if it is long enough! Doesn't take that much either - lol.

I agree, definitely great info to have.

Unfortunately we don't know what kind of coax is being used in that example, or how much of it. It could be 16 feet of RG-58, or 60 feet of LMR-400, or hell 9 feet of RG-174, or some length of something else entirely, so in that regard there is not enough information.


The DB

 

[The DB]

DB you're right, I looked back and found the member I should have addressed, when I referred to your handle. It was in fact Northern35s, that had promised me he was going to do some testing on an A99. He was going to see if scanning his VA1 showed any difference in results...when checking directly at the feed point vs. using a feed line.

Again sorry.

Its not a problem.


The DB