[RadioRay]

Gentlemen, the proof is in the pudding.

Laying aside the formulas and "mumbo jumbo" as some said, my illustration was to simply demonstrate that if this 18 feet coax thing was actually true, then, it would be true for ALL frequencies. That would mean that for EACH band, or frequency, you wanted to use, you would cut a piece of coax a specific length, some of which would be as much as 60 feet long at 3.9 MHZ. OR at 1/4 wave 234/3.9+ around 30 feet----WHATEVER multiplier you think is best, have at it, have a ball! Impress some newbie. Don't WORRY about VF--and, besides, even if it made any difference, you would still would come about at about the same place! WHERE would you put TEN lengths of coax up to 60 feet long in an S-10 pickup--drag it along the ground behind you! :twisted:

The screwdriver takes CARE of it and does it at about 1.2 -1.5 SWR (not "swr-zzzzzzzzzzzzzz"), so WHAT'S the big deal? IF it WORKS, it WORKS! And it DOES work! FOR THE MULTIBAND OPERATOR, IN ANY CASE, IT DOESN'T MATTER!!!!!!!!!!!!!!!!!!!!!!!!!!! I and thousands of other hams have NEVER even given COAX length a second thought, indeed, never ever HEARD of such----until we heard it from the CBers!
And I have installed hundreds of HF radio systems by rolling out how much coax it took to get from the radio to the antenna, tuning the ANTENNA (not the dumb coax), and FORGOT about it.

So as LONG as I can DO that, it WORKS, it will still remain----a CB Myth and Legend like "if I double my power, I'll get double the distance"!

RR

[kc0iv]

Originally Posted by Bandit102

That text about velocity factor was quoted out of a book printed in 1973...Antenna something or other for dummies. My point was to illustrate where the 18 foot myth comes from, largely anyway.

I do run 18 feet in my freightliner with my Predator antenna and get a flat SWR at 25.6 and about 1.2 at 28.5.

Now, on the Moonraker IV at home, I just bought 2 100' rolls of the old RG-8 (Big fat stuff) and get a varying SWR all over many bands but never over 1.85 or so - with a perfect 50 ohms on both the horizontal and the vertical.

The concept of using a coax matching cable length only works of a limited frequency range. As the impedance changes the cable length has to change.

It depends on which Predator antenna you have. If you have the one sold by N9JMX I can see how you can have a bandwidth that covers 25.6 - 28.5 Mhz. Since it has a motorize drive system. If you are talking about the one sold for CB operation there is no way you can that much bandwidth.

The Moonraker IV is simply a Quad antenna that has two driven elements one horizontal and one vertical. The balance of the elements are reflector and directors. There is a pretty good article on the Quad antenna at: http://personal.ee.surrey.ac.uk/Pers...les/behave.htm

After reading this article you will understand why I don't think you can have a bandwidth like what you are saying.

kc0iv

[Bandit102]

While I agree with you that I should not be able to attain that bandwidth with the cb store predator, I assure you, sir, that I do.

[kc0iv]

Originally Posted by Bandit102

While I agree with you that I should not be able to attain that bandwidth with the cb store predator, I assure you, sir, that I do.

Since you agree that the bandwidth can not be that wide something else has to be happening. The most logical would be something is causing the VSWR meter to not give a true reading. Or the meter itself is defective.

One of the things I have seen in some VSWR meters is RF getting into the meter by something other than the inside lead of the coax. Thereby causing the meter to give a false reading. This a common problems with some internal VSWR meters used in CB radios.

If you look at http://www.firestik.com/Tech_Docs/Off-tune.htm you will see a typical VSWR curve. From this curve you see the VSWR ranges from 2.5 to 3.0. Which is typical for most CB antennas.

I haven't done a EZNEC plot on a loaded CB Predator antenna but I suppect it would show a VSWR curve close to what is shown in the firestik article.

kc0iv

[Bandit102]

You are probably correct, sir. I use a $39 Radio Shack 11 meter type power/swr meter. Perhaps I should invest in something more substantial.

[RadioRay]

I would have to agree with KC0IV that something else may be going on here. Contrary to popular thought, being "broad-banded" is not necessary a good thing. In fact, in many cases the opposite is true, and it often indicates that the antenna itself is a "sloppy" radiator. In the CB world, "broadbanded-ness" is a "virtue" tho an incorrect one, but it is used as a sales tool. Granted, some of this trait is garnered by using huge elements (the size of the coil windings themselves), and this "BIGNESS" is always a selling feature: after all, size is always an indication of better, right?

The broad characteristics of Bandit 102"s antenna could be caused by several things, one thing being the very installation itself. How close (or far) is it from metal? Is there something coupling to the antenna at a particular frequency, but it isn't at another---yet it is not readily apparent because you aren't using that frequency at the time. Is there ground potential issues, impedance issues that would cause the SAME antenna to become NARROW-banded on a different vehicle. I've had this to happen when changing to another vehicle, and I worked to get RID of the broadbanded-ness because I know that covering a lot frequencies means that the antenna is less efficient because of it. As a general rule, the narrower an antenna is at a given frequency, the more EFFICIENT it radiates at that frequency. It means that it is, basically, putting the most of its effort into radiating that signal at that frequency. After all, a 50 ohm resistor will load nicely on boo-koos of frequencies. You just ain't got much of a signal on any one them! :wink:


RR[/u]

[BigDiesel]

I ordered this today for both of my trucks !!

http://www.premiere-electronics.net/...nexradios.html

[Jackrabbit379]

Originally Posted by BigDiesel

I ordered this today for both of my trucks !!

http://www.premiere-electronics.net/...nexradios.html

Oooooh. If I had $400 sitting around, I would be owning one of them. :P

[countryhorseman]

If I had and extra $400 laying around, I would more than likely have one of these.

http://www.rangerusa.com/rci-29dx.html

Much more practical, and they come out of the box, with twice what the Connex offers, plus, they are not channelized.

also, I have a license to use those radios also!