This ought to be worth discussion.

[Charlie Brown]

LMFAO

 

[bob85]

you can place the meter anywhere along the line,
if you know the vswr at the point of measurement, the line attenuation per unit length and the distance from the point of measurement to the point along the line at which you wish to know the vswr,

this shit is getting old and disrupting what could be an informative forum..
freecell told you that years ago.

 

[pro151]

My turn with the stupid questions.
Bob85, I understand the VSWR theory or formula if you will, my question concerns the statement I have seen made before (somewhere, don't remember where at this exact moment in time) by some people that they have checked their SWR with the amp on and it is Flat or some "acceptable" reading and then when they switch the amp in-line their SWR does not change.
What are they seeing when they say their SWR is like this in either mode?

 

[Shockwave]

"im pretty sure booty will look into it and im 100% sure doc will not, he will keep posting his usual diatribe without giving it a second thought"

'bob85',
You got that right, maybe. I can't say what 'Booty' will do or not do. I can say that I have given it some thought, it isn't difficult at all. Answer one question for me, if you will. If you want to measure SWR between the feed line and antenna, where do you have to put that SWR meter unless your feed line happens to be an electrical 1/2 wave length long or some multiple of that?
- 'Doc

It sounds like you've already been informed you need to place the meter at the antenna or you need to have a 1/2 wave multiple of coax line in order to be sure the reflected power reading from the antenna is accurate (minus coax loss).

 

[W5LZ]

bob85,
You might read my question again, you obviously didn't before answering. Don't read any more into it than was asked. Now try it again.
'freecell' is an authority? Which 'freecell' are you talking about, there were more than one who posted on this, and other, forums. That was fairly obvious if you just read the posts from 'freecell'.


Shockwave,
I was 'told' that a very long time ago (30 - 40 years?). I've also 'proven' it for my self since being told. That old fart by the name of Rains was right, but then, he was on most of the things he taught. I'd use him for that 'provenance' I'm supposed to quote, but I don't think he ever published anything so probably isn't a recognized 'authority'. The regents of this state thought he was enough of an 'authority' to grant a degree because he said people knew enough to have one, so maybe he was an 'authority? I don't really care since he knew what he was talking about, you know? I do have to stipulate that the 'knowledge'/information he talked about is about 45 years old now, so maybe it's out dated? Physics doesn't change, so maybe it's not out dated.

None of this proves that I'm an authority of any kind, and I don't claim to be! This is all just common knowledge available to anyone who want's it. I would hesitate to say look it up on the internet, that isn't always a good place to look for accurate/true information. I think it's been in every electrical text I've ever opened, so that might be a reliable source.
- 'Doc

 

[Kamikaze]

are you HiDef ?
and why do you keep trying to make money here ?
are you broke or just delusional that what you have to say is worth $$ .

so we tune our antennas to our coax and not to the frequency generated by the radio/amp ?
actually , i think the radio , coax , and antenna impedance all effect each other and they all work best at 50 ohms on the chicken band .

VSWR is the ratio of minimum to maximum voltage on a feedline. Nothing more or less. There are antenna systems which radiate more energy with a 10:1 feedline VSWR than a 1.5:1.

SWR is not an indicator of efficiency. Bandwidth isn't either.

Antenna systems with a lot of bandwidth are generally less efficient than those with a narrow bandwidth. Bandwidth can come from losses. See Double Bazooka, a hair brained antenna.

 

[Kamikaze]

this forum isnt usually about that it is usually more of a technical nature I dont have to do that to make my point but I can if needed been thru many forum wars. Macks just sore I always get the better of him been that way for years somethings never change.


I dont think it is still in the database but at least about 7 or more years ago I was involved in a heated thread with Dr White a professor who had more electrical degrees behind his name, I said you could not check the output swr of a amp, he said you could (along with Doc, and about 50 guys like yourself)saying you could check swr of amp. I gave him a very simple test to do but he must not have had a tube amp or didnt know how to simulate the test he would just argue with me along with 50 wanna bees, I got tossed off the forum even though I was right cause everyone said i was wrong aand argued with me.

Take a tube amp and tune it into your antenna or whatever for max output , take a swr reading, now take the load knob this is the one the controls your output impedance and crank it to the right or left to mistune the amp's output impedance, go recheck the swr, it will be exactly the same as when you started because the SWR meter doesnt care or know what the source impedance is it checks the swr of coax to the load.

That's because SWR is only a ratio of max to min voltage or current on a feedline.

Professors and engineers can be wrong. They are only people.

 

[hookedon6]

...Professors and engineers can be wrong. They are only people.

Well,.... JEEZ, why didn't ya say that 9 pages ago op:


BTW: why do coax manufactures recommend that you NOT put sharp bends in the coax?.......

the radio's output impedance hasn't changed,....
the antennas impedance hasn't changed,....

but guess what DOES change,.....

think about it.

 

[W5LZ]

"That's because SWR is only a ratio of max to min voltage or current on a feedline."

Right! Which does have a relation to impedance ratio too.
- 'Doc

 

[bob85]

151,
they are seeing that vswr does not change with power level,
their amp is not break dancing like a palomar,
the radio output was high enough and line loss low enough to not be putting the meters detector diodes in their none linear conduction zone,

they are not seeing that their amps output impedance is 50ohms as doc claims.

 

[Kamikaze]

"That's because SWR is only a ratio of max to min voltage or current on a feedline."

Right! Which does have a relation to impedance ratio too.
- 'Doc

And that concept stops being simple as soon as the impedance is complex ie: not purely resistive.

 

[BOOTY MONSTER]

BTW: why do coax manufactures recommend that you NOT put sharp bends in the coax?.......

if i remember correctly ................
the impedance of coax is determined by the diameter of the center and shield conductor and their distance from each other . putting too tight a bend in the coax or pinching/denting it through a tight spot will cause the distance between them to change .......... and change the impedance of the coax .

 

[GnG8d]

if i remember correctly ................
the impedance of coax is determined by the diameter of the center and shield conductor and their distance from each other . putting too tight a bend in the coax will cause the distance between them to change .......... and change the impedance of the coax .

True, but you don't tune the coax to the antenna, you tune the antenna to the coax, right?

 

[bob85]

doc,
im not reading anymore into it than you asked, either you misunderstood rains or he was wrong too,
you have not proven anything but a lack of understanding of this simple concept you speak of and disrupt the forums with,

i do agree there was more than one freecell posting on here.

 

[bob85]

hookedon6,
the sharp kink can move the center conductor or squash the outer sleeve which causes an impedance discontinuity from which reflections will occur setting up an interference pattern of standing waves on an otherwise flat line, a look at the line with a time domain reflectometer can highlight the issue and tell you where the kink is along the line.