Coax Length Question

Which indicates to me if I need a question answered about complex RF wave equations I cannot turn to you because you do not understand the theory. Neither does any 'guru', Ham operator, or in general anyone else who goes with the flow not understanding and not wishing to stand out by making claims that go against the traditionally stated mindset. The mindset being "To me, it proves that, minus all the hocus-pocus, stripped of all the hoopla and CB legend, coax length is simply a bunch of horse manure!"

Yet the answer was all along simple, involving common mode currents on the coax shield. If you are trying to push a boat on the water it is best not to do so when standing on a board floating on the water at the time.

One with credentials better than most on the subject discussed the issue coming to the conclusion the condition exists when the antenna is improperly designed (in His case it was an improper matching system given feedpoint conditions). Stated correctly "improperly designed for where, on what, and how it is mounted, how it is fed, and so on". I speak of W8JI, an outstanding person when it comes to measuring antenna systems. Read what He said about the IMAX 2000.

http://www.w8ji.com/end-fed_vertical.htm

In the case with Mike, it is not so much improper antenna design, rather improper truck design as it concerns any hope of an antenna performing well. By this I mean such antenna designs commonly available for use on 18 Wheelers which one can easily find in the typical truck stop. More accurately one could say Mike is in a poor truck. Nothing wrong with the antenna, just a truck design unfriendly to all modern CB mobile antennas.

Say we pick a Wilson 2000. Assuming the shaft is long enough to reduce any circulating eddy currents in the vehicle body, one cannot say the antenna is a poor design. Rather, it is a design with high feedpoint current requiring good ground. RF being three dimensional in terms of standard field equations, means the geometry is important. A copper disk 18 feet in diameter, W2K in center on 18" shaft, performs fairly well. However rather hard to get down the highway with. So going back to the problems Mike is having, He cannot get a decent counterpoise so common mode currents give rise to excessive SWR measurements. He fudges around with coax length and obtains performance adequate for His needs even if it achieves say 40 percent less range than the copper disk counterpoise I mentioned. Put simply with the 18 foot copper disk you are standing on solid ground when trying to push the boat, as opposed to the board floating on the water. In this instance the 'push' relates to driving enough current into the coax center conductor to create a strong enough magnetic field to generate the required near field to achieve decent performance. In Mike's case he is dealing with a resistive, reactive, ground with excessive loss.

In summary instead of making the statement I quoted above, try to gain understanding as to what is actually going on. Such statements fail to take into account what is actually occurring indicating to me a lack of true comprehension.

 

I'm learning...............pretty good explanation there Outlaw.

 

Lotsa bees and "swr'zzzzzzzzzzzzz a-buzzin' around!

GF

 

It should be known in the CB world, you MUST have:

Echo
Roger Beep
Extra channels not on the CB frequencies
Rebel flag faceplate
Illuminated knobs (at least two can be Betty's boobs)
Blue channel LED and blue backlit TX/RX meter
At least two noise toys installed
A swing kit installed
All internal variable resistors (aka "pots") turned to the max
A power mic to supplement the mic gain
All modulation limiters clipped
Small 4 ft antennas, preferably obscured by metal on one side
Whatever C class HF amp you can conjure up (just call it a linear, even if it's not really "linear")
And last but not least.....18 feet of coax...at a minimum

 

So one can assume then a logical, intelligent, reasonable discussion is not the goal of anyone here? Like Pavlov's dogs coming back with a conditioned response in lieu of knowledgeable discourse. I see. If as you all claim coax length makes no difference then one nagging question arises. Why do you all endlessly harp about 18 feet since as you say length does not matter? Why cannot you just be happy with whatever length a CB'er chooses so long as it fits within the domain of 'any' length? What is it about this one length that drives you all so insane raving against CB operators and forever putting them down, i.e., making endless fun of their stupidity when one considers the fact that 18 fits within the set of all numbers fitting the description of 'any'?

One can therefore only come to the conclusion that within the group of all radio operators not in the group of CB'ers, there is an extreme shortage of Prozac out there.

 

I never said you had to have 18ft of coax! NEVER! And that hasn't even been what the discussion was about. But, people read/see what they want to see I guess.........time to move on with this one I suppose. (OBTW, you won't find any of my radios in the condition(s) you described above.......FWIW)

 

Hehehehe

 

if you want the best coax go to jefratech.com its made in maryland lmr240 is the type and i personally have 10ft installed in my trk and have perfect swr the whole lenth deal is crap..... aslong as you have a good ground and enough whip you could go as short as you wanted

 

Mike,

I thought you ran a 3300? Doesn't it have a Betty Boop face plate????

 

I run a 3300HP in the truck, with a American Flag face..........and only one noise toy!...........not