The myth of coax length.

[Captain Kilowatt]

No, you wouldn't. All you would need to do is match the impedance to the feed point. That being said, I have seen such a setup, what was it called, something like a T match?
The DB

A TEE match is used on a balanced antenna. I have such matching devices on my 13B2 yagis for 2m. They are fed with a balun at the feedpoint and use a TEE match. FWIW the diagram posted by M0GVZ that sparked this tangent is actually of a balanced antenna fed with balanced feedline and NOT coax cable.

 

[Tallman]

Bias T's are used to inject DC voltage into a coax line to power a mast head amp at the top of a tower. This is something I had to deal with myself.

I used to install those systems LNB or LNA's, and we always had to load test the 18 VDC at the top of the mast. Dragging that dummy load and meters up the tower was always the New Guy's job until another new guy came on board.
Sean be safe and keep your eyes open. Prayers are being said.

 

[Captain Kilowatt]

No they don't conflict, both are true,
you don't understand the difference between impedance looking into a mismatched line and vswr at any point along that line,
two different instruments two different measurements,

you said
"This is exactly how misconceptions are started. It's ALWAYS best and prudent to verify any and all information from respected sources before committing them as fact in your head"

yes i agree,

Exactly. I stated this is post #12. I remember waaay back many many years ago I had a hard time wrapping my head around the fact that while the impedance changes along a line the SWR did not. After all, impedance affects SWR right? Then I learned that various combinations of X and R will result in the same SWR value. Most people do not understand this.

 

[The DB]

True, but the braid does not go positive. In coax only the center is conducting the power. The voltage is induced in the other element.

At this point I have to request a source. What you are saying here is a direct contradiction to everything I have read on this, and I am extremely well read on this topic.

I stand by what I said, the power, voltage and current are in phase with each other, even the other phase that you said is 180 degrees out of phase with each other. Voltage and current are in phase.

This has nothing to do with what I was referring to in the quote you referenced. I am wondering why it was brought up here.

There is a Wilkerson circuit that allows a 50 Ohm transmitter to drive two 50 Ohm antennas with only a 50 ohm single input

I am aware of the Wilkinson Power Divider, its a neat device, using nothing but passive components it provides full isolation between its two outputs. I am not familiar with anything that goes by the name Wilkerson. However, I fail to find how this is relevant to what I said, or the context I was using. Being a neat device that can take a 50 ohm input and give you two separate 50 ohm outputs that are isolated from one another is one thing, but I fail to see what that has to do with matching one impedance to another and me saying your requirement of using a double gamma on a beam is not accurate. The only thing I can think of that might be related to the Wilkinson Power Divider is the T match I referred to offhand, which is essentially the double gamma you referred to, one on each of the feed line elements...


The DB

 

[Tallman]

I remember waaay back many many years ago I had a hard time wrapping my head around the fact that while the impedance changes along a line the SWR did not.

The first word give away the characteristic, "Standing" Wave Ratio.
I had trouble understanding "FM". The class just started calling it "F*****g Magic."

 

[Road Squawker]

[QUOTE="222DBFL, post: 564988, member: 36544"... the best way to tune an antenna with an a analyzer is by using a quality piece of coax 12 inches or less in length... Yes you can use an electrically tuned 1/2 wave coax or a multiple of one, but connecting directly to the feedpoint removes any and all possibly issues...
Again, to all, have a great day!! Sean.[/QUOTE]

OK, ................ don't you think that standing close to the antenna and operating a manual calibrated meter connected with only one foot of coax will affect the antenna resonance?

 

[Tallman]

At this point I have to request a source. What you are saying here is a direct contradiction to everything I have read on this, and I am extremely well read on this topic.

I am aware of the Wilkinson Power Divider, its a neat device, using nothing but passive components it provides full isolation between its two outputs.
The DB

Aren't you being overly nit picky on a typo? If the braid goes Positive as you suggest mobile mounted radio communications would be impossible. The entire car chassis would have to carry that electrical charge and I don't believe it does.
I do believe you are very well read on the subject.

Tallman said: ↑
I stand by what I said, the power, voltage and current are in phase with each other, even the other phase that you said is 180 degrees out of phase with each other. Voltage and current are in phase.

This has nothing to do with what I was referring to in the quote you referenced. I am wondering why it was brought up here.

Because you were in error and I needed to provide correct information. Just trying to keep this on an even keel.

 

[Tallman]

OK, ................ don't you think that standing close to the antenna and operating a manual calibrated meter connected with only one foot of coax will affect the antenna resonance?[/QUOTE]

Yes standing in the area of the antenna will influence the readings, but 222DBFL was referring to using the antenna analyzer. You can set up the analyzer and back away from and read it from a distance using binoculars. Any metal in the area will influence the readings. Metal fences, trash cans, cars, and power wires will influence the readings. Even the analyzer hanging there will change the readings as well.

 

[The DB]

Aren't you being overly nit picky on a typo?

That was more a making sure we were talking about the same thing. It is possible that there was something I hadn't heard of called the "Wilkerson circuit" so I was just trying to make sure we were talking about the same thing.

If the braid goes Positive as you suggest mobile mounted radio communications would be impossible. The entire car chassis would have to carry that electrical charge and I don't believe it does.

Actually, the entire chassis of a car does carry a charge, or at least some portion of it, at least all of it that is electrically connected to the antenna. Think of it this way, if no antenna mode currents flowed on a vehicle chassis you could remove said chassis from the mobile antenna and that would not change the tune of the antenna, or its performance characteristics. Further, things like RF bonding would also have no effect, and rf bonding has been shown to have a definite effect on not only a mobile antenna's tune, but its performance as well.

If RF currents cannot flow or are not flowing on something then that something is invisible to said RF, and said antenna will work just as well if it wasn't there.


The DB

 

[Tallman]

Tallman said: ↑
True, but the braid does not go positive. In coax only the center is conducting the power. The voltage is induced in the other element.
DB said:
At this point I have to request a source. What you are saying here is a direct contradiction to everything I have read on this, and I am extremely well read on this topic.
Tallman said:
I know that eddy currents are induced in the sheet metal, but if you are running a Thousand watts does that mean there is 1 Kw potential between the vehicle and earth ground? I'll say it again only the center conductor carries the potential. if the braid goes that far positive you have some very bad coax. The braid is just like the neutral line for AC power wiring. It is the return line for the power.

 

[The DB]

I did a full quote of a message, and after I finished typing I find more was added to said message.

I stand by what I said, the power, voltage and current are in phase with each other, even the other phase that you said is 180 degrees out of phase with each other. Voltage and current are in phase.

I did mention at one point that power provided from a power company was out of phase, however, and I realized that I didn't remember where I had heard that and admitted that I needed to double check on that. However, that has absolutely nothing to do with why I posted the comment you were referring to. There is a very good reason that power on both wires are 180 degrees out of phase, and that reason is what I was referring to. This extends to three phase power, with all three of its wires that are 120 degrees out of phase.

Because you were in error and I needed to provide correct information. Just trying to keep this on an even keel.

What you said there was a true statement, but was irrelevant to what I was referring to. It is like you got hung up on one side statement that was really not meant to be part of the main conversation, more of a cool little bit of extra info, and used that as the ultimate context for everything I said and intended. You missed my points to such an extreme that your responses are completely irrelevant to what you are responding to.

I know that eddy currents are induced in the sheet metal, but if you are running a Thousand watts does that mean there is 1 Kw potential between the vehicle and earth ground? I'll say it again only the center conductor carries the potential. if the braid goes that far positive you have some very bad coax. The braid is just like the neutral line for AC power wiring. It is the return line for the power.

I'm going to stop here because this is getting ridiculous.

An antenna system can radiate an EM field that induces both a voltage and current in another antenna system thousands of miles away strong enough for said radio system to receive your signal, yet this metal less than 1/4 inch away for the entire length of the feed line and thus subject to a much stronger EM field for generally a much longer length somehow follows different laws of nature and thus won't be affected by said RF field? I'm sorry, your going to need one hell of a source on that one.

I am going to take what I am saying a step further, and disagree with something you are taking as absolute fact. If RF is not flowing on the inside of the shield, antennas would simply not function as they do with coax. Further, many of the aids we use such as the smith chart would also not work as they do with coax (the smith chart works beautifully with coax). My VNA, and many if not all of its functions, as well as all of the antenna analyzers out there, would not, in fact could not, work as they do. Modeling software, whose results have been shown by experts to be within a small margin of being accurate with real world testing, even though coax was used as a feed line, are all mistaken. The authors of all of these books on antenna and radio theory, from the ARRL to books used to train engineers on the subject are all wrong.

That is an extraordinary claim you are making and treating as absolute fact, where is your extraordinary evidence?


The DB

 

[Tallman]

Let us just agree to disagree on some points. The three phase power is 120 degrees from each other, but the voltage and current are in phase in each individual phase.
The power supplied by the power company can not be capacitive. I guess since all motors are inductive you thought resonance must be reached through rotation. Single phase 220 is the only power that is 180 out of phase with the other line. 110 VAC and 180 apart is the other 110VAC hence you get 220 VAC.

You are the one who needs to prove the positive voltage shift on the car chassis.
It does not happen in realm of Theory or real world.

I did a full quote of a message, and after I finished typing I find more was added to said message.



I did mention at one point that power provided from a power company was out of phase, however, and I realized that I didn't remember where I had heard that and admitted that I needed to double check on that. However, that has absolutely nothing to do with why I posted the comment you were referring to. There is a very good reason that power on both wires are 180 degrees out of phase, and that reason is what I was referring to. This extends to three phase power, with all three of its wires that are 120 degrees out of phase.



What you said there was a true statement, but was irrelevant to what I was referring to. It is like you got hung up on one side statement that was really not meant to be part of the main conversation, more of a cool little bit of extra info, and used that as the ultimate context for everything I said and intended. You missed my points to such an extreme that your responses are completely irrelevant to what you are responding to.



I'm going to stop here because this is getting ridiculous.

An antenna system can radiate an EM field that induces both a voltage and current in another antenna system thousands of miles away strong enough for said radio system to receive your signal, yet this metal less than 1/4 inch away for the entire length of the feed line and thus subject to a much stronger EM field for generally a much longer length somehow follows different laws of nature and thus won't be affected by said RF field? I'm sorry, your going to need one hell of a source on that one.

I am going to take what I am saying a step further, and disagree with something you are taking as absolute fact. If RF is not flowing on the inside of the shield, antennas would simply not function as they do with coax. Further, many of the aids we use such as the smith chart would also not work as they do with coax (the smith chart works beautifully with coax). My VNA, and many if not all of its functions, as well as all of the antenna analyzers out there, would not, in fact could not, work as they do. Modeling software, whose results have been shown by experts to be within a small margin of being accurate with real world testing, even though coax was used as a feed line, are all mistaken. The authors of all of these books on antenna and radio theory, from the ARRL to books used to train engineers on the subject are all wrong.

That is an extraordinary claim you are making and treating as absolute fact, where is your extraordinary evidence?


The DB

 

[Road Squawker]

OK, ................ don't you think that standing close to the antenna and operating a manual calibrated meter connected with only one foot of coax will affect the antenna resonance?

Yes standing in the area of the antenna will influence the readings, but 222DBFL was referring to using the antenna analyzer. You can set up the analyzer and back away from and read it from a distance using binoculars. Any metal in the area will influence the readings. Metal fences, trash cans, cars, and power wires will influence the readings. Even the analyzer hanging there will change the readings as well.[/QUOTE]

or,... you could just use an odd mult of wl/2 elect length of coax.

the point was about the 1 foot of coax being the "best" way to tune an antenna

BTW, I don't think I have ever seen anyone use binoculars to read an analyzer,.... as they say on Monday Night Football,.................. "COME ON, MAN!!!!"

BTW #2 Did you just upgrade recently (like yesterday)?

 

[The DB]

Let us just agree to disagree on some points.

I'm ok with this. I have no problem with letting bygones be bygones.

The three phase power is 120 degrees from each other, but the voltage and current are in phase in each individual phase.
The power supplied by the power company can not be capacitive. I guess since all motors are inductive you thought resonance must be reached through rotation. Single phase 220 is the only power that is 180 out of phase with the other line. 110 VAC and 180 apart is the other 110VAC hence you get 220 VAC.

Are you seriously still stuck on that? Post # 42 on this thread I wrote:

You might be right, I am trying to remember where I heard that. I'll have to look into that more I guess.

Nothing I have posted about since had anything to do with the phase relationship between voltage and current in the same wire in an electric companies power drop. You are harping on something that was neither said nor implied in anything I talked about since. There are other aspects of the power system that could be relevant to this discussion, but with you blindly assuming that this is all I am ever talking about with power systems even though what I am saying has absolutely nothing to do with your responses. Seriously, if you haven't even noticed that what I am talking about with power systems is not about said topic by now, how can I expect you to keep up with anything I would say? You need to get over this one line I said. If you can't do that you are only holding yourself back.

Now, if I choose to go back to that point and say that again, by all means, harp away, but i haven't, and don't intend to, at least until I have a chance to confirm this independently.

You are the one who needs to prove the positive voltage shift on the car chassis.
It does not happen in realm of Theory or real world.

You brought up about agreeing to disagree on some points. I have no problem with this if you don't. I'll end it here as long as you do as well. The choice is yours.

I guess I don't get to tell the story of my first RF burn... Thats no fun...


The DB

 

[Tallman]

Okay with me. You know how it goes, some days chicken, some days just feathers.