Why is my SWR always changing????

[Captain Kilowatt]

The Length of Coax can also have an effect on the Actual SWR, which is another reason to Test at the Antenna...
Just something else to think about...

NO this is not true. The SWR will remain constant along the cable. The actual impedance however will change but that complex impedance will always work out the same SWR. Yes there are many values of reactance and resistance that will create the same value of SWR. A Smith Chart will show that. What DB was talking about thelength of cable making a bad SWR look good is due to losses on the return making the reflected power look much smaller than it really is thus making the SWR look lower than it really is. This is assuming the reading is taken at the end of a long run of lossy cable.

 

[The DB]

You started it with saying, I was wrong... You chose to discredit me for no reason...You CANNOT prove anything I said, was wrong... No one can... There is no Right or Wrong as everyone's Equipment varies... You can believe anything you want...

What I stated about SWR meters is exactly correct. They don't know what happened before them, and aside from a change in the total forward power have no ability to tell that a change has even happened before them in the chain.

How to prove what you stated was wrong... hook up a radio into an antenna tuner. Then antenna tuner to a load. I wouldn't use a perfect match although you could, the load I used had 4.5:1 SWR. I wouldn't use an antenna to eliminate the possibility of various issues, such as CMC's. For this test it is also a good idea to not have an electrical quarter wavelength multiple of coax, but again, you can. Put an SWR meter between the tuner and the load. The tuner simulates the change in the radio, and can do this job very well as you can simulate nearly any R+-jX combination with it, which is more than the radio tuning circuits is likely capable of generating. I would use the radio on low power as you will likely be transmitting into a high SWR. Measure SWR on the meter and record. Change the settings of the antenna tuner and measure the SWR again.

I've done this, and initially got different results, which are contrary to what the ARRL Antenna Book series said should happen. A broadcast engineer that posts on this forum caught my mistake, and when I ran the test again it matched what should have happened, and what was written in said ARRL Antenna Books. It is you who disagrees with said books that you cited as a reference, not me.

The only difference between Right and Wrong is a matter of one's Opinion...

Right and wrong, in this context, are not based on opinion. We are not talking morels, but what happens in reality. However, in this context a persons perception of what is right and wrong can be based on opinion...

Throw an Antenna Tuner inline and one can fool any meter to read anything...

That depends on where the SWR meter is in the system, see above...

If saying I was wrong makes you feel better, great...

I'm not interested in feeling good, that wasn't the point at all, and if you took it that way then you missed the point entirely.

Why people chase Rainbows, I'll never know... ALL My Radios work and I am the one who works on them and that is Good enough for me...

I didn't chase rainbows, I know their is no pot of gold at the end of a rainbow, actually, I know most rainbows in nature are actually completed circles, you just never see the entire circle...

Have fun with those radios, having fun is what the hobby is about.

No, I am not a Licensed HAM as I do not like the HAM Superiority Complex...

I don't need / want a License, it's ONLY Radio...

I really want to say something here, but it could be perceived as a personal attack, and that is not my goal.

I will say that I hang out with both ham and CB operators, and in my experience what both groups say about each other is about half correct. I will say this, its not the class of the license but the class of the operator.

Also, as you only have few posts I'll say this assuming you are new here. This is a very technical forum, it isn't uncommon for a technical debate to breakout in the middle of a thread like this. If I didn't say anything someone else very likely would have, and the anger you displayed (or at least I felt from you) would have been directed at someone else. If it didn't happen in this thread it would have happened in another thread. If this happens again don't assume it is personal, it is not, and no ill intent is being directed at anyone. The best thing to do is explain your case, and put in as many references as you can. Who knows you might just learn something, I definitely have over the years. Honestly, I have likely learned just as much about antennas participating in discussions and asking questions here as I learned from the ARRL Antenna Book series. This forum really is a great resource for those who want to know about antennas, and radio in general.

 

[Captain Kilowatt]

What I stated about SWR meters is exactly correct. They don't know what happened before them, and aside from a change in the total forward power have no ability to tell that a change has even happened before them in the chain.

How to prove what you stated was wrong... hook up a radio into an antenna tuner. Then antenna tuner to a load. I wouldn't use a perfect match although you could, the load I used had 4.5:1 SWR. I wouldn't use an antenna to eliminate the possibility of various issues, such as CMC's. For this test it is also a good idea to not have an electrical quarter wavelength multiple of coax, but again, you can. Put an SWR meter between the tuner and the load. The tuner simulates the change in the radio, and can do this job very well as you can simulate nearly any R+-jX combination with it, which is more than the radio tuning circuits is likely capable of generating. I would use the radio on low power as you will likely be transmitting into a high SWR. Measure SWR on the meter and record. Change the settings of the antenna tuner and measure the SWR again.

I've done this, and initially got different results, which are contrary to what the ARRL Antenna Book series said should happen. A broadcast engineer that posts on this forum caught my mistake, and when I ran the test again it matched what should have happened, and what was written in said ARRL Antenna Books. It is you who disagrees with said books that you cited as a reference, not me.

Hmmmmm.....I wonder who that would have been?

 

[The DB]

NO this is not true. The SWR will remain constant along the cable. The actual impedance however will change but that complex impedance will always work out the same SWR. Yes there are many values of reactance and resistance that will create the same value of SWR. A Smith Chart will show that. What DB was talking about thelength of cable making a bad SWR look good is due to losses on the return making the reflected power look much smaller than it really is thus making the SWR look lower than it really is. This is assuming the reading is taken at the end of a long run of lossy cable.

Bingo, you nailed what I was talking about here.

To restate the smith chart example in my words...

The smith chart, love those, that is a great tool to learn about feed lines and antenna matching. The X and R variables (aka complex impedance) along a theoretical lossless feed line will create a circle on the smith chart, and on that circle will be every possible combination of X and R that creates that SWR value. The center of the circle is the center point of the smith chart and a perfect match. All points that is a given distance from said center point have the same SWR, this forms an "SWR circle". The circle that the theoretical lossless feed line creates is a perfect match to this "SWR circle".

Once you add losses to the feed line the circle created by the feed line will become a spiral towards the center of the chart, with enough feed line it will eventually get to a perfect match which, again, is the center point on the chart, this happens irregardless of the starting mismatch. The lossier the coax the faster the spiral spirals inwards. What this is telling us is that the more losses there are in the feed line the better the match will appear to be on the radio end of the feed line.

If you have a situation where a short change in the length of coax makes a large change in SWR, then you have a problem that needs to be dealt with. Generally this is caused by common mode currents, a ground loop would be the next biggest cause, I have also seen a bad piece of coax do this.


The DB

 

[The DB]

Hmmmmm.....I wonder who that would have been?

Actually, I think it was Shockwave, who hasn't posted in a while. Neither you nor he has lead me astray yet... Two great resources right here, even if he hasn't posted in a while.

There are also other very knowledgeable people on this forum as well. It is not a small list of people to pay attention to here, and that is a good thing.


The DB


NOTE: For those that don't know the "you nor he" is referring to people that currently or have in the past worked as broadcast engineers.

 

[Captain Kilowatt]

Actually, I think it was Shockwave, who hasn't posted in a while. Neither you nor he has lead me astray yet... Two great resources right here, even if he hasn't posted in a while.

There are also other very knowledgeable people on this forum as well. It is not a small list of people to pay attention to here, and that is a good thing.


The DB


NOTE: For those that don't know the "you nor he" is referring to people that currently or have in the past worked as broadcast engineers.

I only posted that because the only two former/current broadcast engineers on this forum that I thought of is Warren, VO1KS, and myself. I forgot all about Shockwave. Sometimes I have a brain fart and confuse the name with Jeff aka Audioshockwave. LOL In my defense I did spend over ten hours yesterday sitting in front of a stage at a music festival in town here. It was the first day off of my 22 days. I am a little sunburnt, a little dehydrated, and a little deaf and rattled and probably not thinking REAL clearly at the moment.