Coiling the coax cable causing problems....a myth or fact?

[Mr.5150cbrn]

I have to wonder if people actually read the entire thread when they dig up older ones like this. Maybe they just read the last post or two and then comment without looking at everything that was posted before. I also wonder how many listen to myth and conjecture rather than proof and experience. :headbang :bdh: :bdh:

without reading the whole thread , making an assumption and posting will continue the the endless forum experience , and moments of endless entertainment.
at someone else's expense
for if it wasn't for :headbang and:bdh: :bdh:, the majority of most threads would be short , dull , and not viewed !
its a part of the human experience of trial and error.
as most all of these topics are covered in the arrl handbook, but without the KEY ingredient humor and smileys!
if the handbook had integrated those key ingredients , maybe that book wouldn't be sitting on the shelf collecting dust from the lack of use,
and if the latter was applied - maybe the forum would be short dull and un entertaining ?
as thats just my thoughts

 

[unit_399]

I think that something that people are 'missing' is that choke, that coil of feed line, only affects what's on the outside of that feed line, not what's on the inside of that feed line. The only significant affect a choke has on any feed line is that it adds some length to it. That can mean some loss because of resistance, but for the lengths commonly used to make up that choke, that resistance amounts to very, very little. Notice that I said 'resistance', not impedance. If the impedance of the -system- is changed because of that added length, then the antenna (load) on the end of that feed line is incorrectly tuned. Meaning that it is not the same impedance as the feed line and the transmitter. That holds true for any transfer of AC energy no matter it's frequency, 27 Mhz or 60 Hertz, or audio frequencies, anything AC.
- 'Doc

DOC -
So you're saying that you can adjust the impedance (and the match) of an antenna system by varying the length of the coax ??? Since when .

 

[hookedon6]

DOC -
So you're saying that you can adjust the impedance (and the match) of an antenna system by varying the length of the coax ??? Since when .

be careful,..... I made statements to the effect that: if varying the coax lenght causes the VSWR to change, then, there are other problems present,...... and my PM box got bombarded by the people that repeat CB "facts"

yeah, yeah, yeah, I know,........ "but, my meter tells me my SWRS do change when I add coax...."

 

[Captain Kilowatt]

DOC -
So you're saying that you can adjust the impedance (and the match) of an antenna system by varying the length of the coax ??? Since when .

Yes if you include the transmission line as part of the SYSTEM and it has always been that way. The "gotcha" part is as Doc and others have already stated (there goes that reading all the posts part again) is that changing the coax length will only alter SWR at (the shack end of the cable) if the antenna is not a true 50 ohms.The antenna feedpoint impedance does not change regardless of how long the transmission line is. This changing of length affecting SWR thing is why people still ask how long their cable has to be between their radio and amp to get a good match. It is because their amp does not present 50 ohms to the radio and they are attempting to alter the SWR by changing the feedline length between the amp and the radio which works but is only a bandaid solution to a hemorrhage AFAIC.

 

[AudioShockwav]

Do you guys know who Max Headroom is?
This thread reminded me of him from way back when...

73
Jeff

 

[hookedon6]

...
for if it wasn't for :headbang and:bdh: :bdh:, the majority of most threads would be short , dull , and not viewed !...

I think we need an ICON for repeatedly "kicking the same can, down the same road"
op:
op:
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oh,...... did I say

 

[Captain Kilowatt]

Do you guys know who Max Headroom is?
This thread reminded me of him from way back when...

73
Jeff

Yep. IIRC it seems M-M-M-M-MMMMM-----Max struck his head on something too.

 

[Turbo T]

Do you guys know who Max Headroom is?

Yep...a computer generated guy on TV back in the 80's.

 

[Captain Kilowatt]

I think we need an ICON for repeatedly "kicking the same can, down the same road"
op:
op:
op:
op:


oh,...... did I say

I looked in my collection but couldn't find anything like that. Will this do instead?

 

[unit_399]

Yes if you include the transmission line as part of the SYSTEM .

OK ... I misunderstood Doc's post, which happens a lot. Lo siento.

- 399

 

[Captain Kilowatt]

OK ... I misunderstood Doc's post, which happens a lot. Lo siento.

- 399

Sometime you have to ask just what someone considers the antenna system. Some people believe that the only thing in an antenna system is the antenna itself while others consider everything after the radio/amp part of the antenna system including any switches, transmission lines, baluns etc. as well as the actual antenna. Some even refer to an antenna system as a bunch of different antennas together for the same or different bands.The generally accepted definition in professional circles (design engineers, RF workers etc.) is that the antenna system includes the antenna as well as the transmission lines and anything else in the RF path.

 

[pro151]

You would be amazed at the number of people that think the signal flies out of the very tip of the antenna just like in the cartoons. :laugh:

 

[mackmobile43]

You would be amazed at the number of people that think the signal flies out of the very tip of the antenna just like in the cartoons. :laugh:

Here is proof you're wrong!

 

[Blue Jay]

I looked in my collection but couldn't find anything like that. Will this do instead?

I like it**Jump_im**

 

[KM3F]

Lets try this all again.
There are TWO conditons possible in an antenna 'system' that includes the antenna AND the transmission line (known as the coax).
1. With a perfect match between the transmission line and the antenna there is no reflected power (known as SWR). Therefore the coax length has no length reguirement and no SWR so coiling has no effect.
2. With a missmatch "at the antenna", power not radiated will return back through the (inside) and some on the outside of the coax and is the swr you can measure with a meter in line.
The power that come back on the outside is called common mode.
Both the return power inside and outside will be sensitive to line length changes and even hand capacity indicating there is a match issue at the antenna.
.
To conlude this, a 'near' perfect match at 1 to 1 or close in not line length sensitive.
There is no return power inside or out so coiling in any manner does nothing.
However if there is a missmatch as indicated be an SWR meter, the length will be sensitive 'AT THE POINT IN THE LINE IT IS MEASURED'. This means if you lengthen or shorten the line, the SWR reading will change ON THE METER ONLY. It does not change the missmatch at the anternna. You are only fooled into thinking a missmatch has been corrected unless you know better.
Under missmatched conditions and high SWR, power can return on the outside of the coax.
With this conditon, coilng the coax forms a choke that impedes the power coming back on the outside due to the missmatch at the antenna.
Listening to the CB experts only perpetuated a lack of knowledge they have and you keep passing it on to others.
Anyone doubts this, research it in antenna books on transmission lines and see for yourself instead of being led by people who just think they know.
Referring to incorrect sources is not proof otherwise.
Print this out and save it for reference next time there is a debate about it.
Good luck.