Why the gain?

[The Jerk]

Doc:

That's why I was asking...I don't know antenna theory and didn't want to spend $$$ on a "better" antenna if in fact it wasn't really an improvement. After reading all this, I will be staying with my 102...doubt I would see enough improvement over my 102 to justify the purchase.

About the only coiled antenna that would sort of work in this situation would have been a 27" Predator 10k mounted in the same location as the 102...the roof is too light of material to support an antenna of that size, even with significant reinforcements.

And again, I'm sure you've read the claims of others that indicate significant improvements by switching antennas. The one I read the other night indicated two s-units of improvement in TX and three s-units of RX, which is not a trivial amount (but I don't know how each antenna was mounted either). But at the same time there are articles that state the 1/4-wave is the ultimate antenna. I just wanted to see others' opinions...before I did something foolish...


Booty:

My 102 is mounted on a solid mount without a spring (spacer), it leans back about 12 inches at highway speeds. I believe the shape of the truck forces a lot of air upward, and the antenna isn't subjected to as much of a side load. So I don't see much deflection or "walking" while driving, unless I am driving into a decent headwind.

The solid spacer makes a significant improvement over the spring...a lot less "walking" and lean than the spring.

 

[kor b]

hhhmmmmmmmmmmmmmmmmmm.... good egg nogg

i wonder how a fiberglass 102 with a solid/allthread spacer in place of a spring centered on a tool box on lil truck compared to a 17 or 22 inch 10k on the same roof would compare ? should be a lot straighter when driving.......?????

Per Lou Franklin "Screwdriver Expert's Guide" copyright 1994

"Have you ever noticed that fiberglass whips are shorter than steel whips? They're 96" to be exact. Reason: The fiberglass whip is essentially a copper wire embedded in fiberglass; in other words, a "copper whip." Your CB radio is generating radio waves at 27 million times per second. But even at this incrdible speed, it still takes a definite amount of time for the radio wave to travel from one end of the whip to the other end. Since copper is a much better conductor of electricity than steel, the same wave shoots through the copper much faster. So in other words. the fiberglass-copper whip doesn't have to be as long for 1/4 wave of the CB signal to "fit" on the whip.Technically. this is called "propagation delay." But both types perform equally well."

Take it for what its worth.

 

[Robb]

I'll buy what kor b said. The real differnce between the steel whip and the fibreglass/copper is sensitivity. The steel whip lends itself to recieving real signals, while the copper/fibreglass tends to pick up more noise. The differnce in the materials being the real factor in practical tems.

 

[W5LZ]

kor b,
I'm afraid that 'quote' is just sooo wrong, in more than one way. I would suggest finding out just exactly what "propagation delay" and "velocity factor" mean. As evidenced by that 'quote', Mr Franklin didn't have a clue. Those two terms mean exactly the same thing, just being expressed/said differently, and used inappropriately in that 'quote'.
The reason a typical fiberglass 1/4 wave antenna is shorter than the typical 102" steel whip is because the copper conductor in that thing is wound around the fiberglass core, making it a helically wound, shortened/loaded, antenna. Of course it's shorter than a straight run of conductor!
There IS a difference in conductivity between copper and steel, copper being slightly more conductive than steel. That difference in conductivity just isn't that much, and will make very, very, very little difference to RF, if any practical difference at all. And since that steel whip has an average larger diameter than the copper wire in that fiberglass antenna, the steel whip should be shorter, not longer. Diameter of a conductor does make some difference, that's well documented, I see no reason to try proving it here (called 'skin-effect', by the way).
Having been familiar with Louis Franklin's work for quite a few years I think that's a mis-quote. He was smarter than that.
- 'Doc


And just for 'grins', both copper and steel, whether on, or wrapped in fiberglass, behave exactly the same way as antennas. Neither has any 'preference' for noise. That's another one of those 'myths', no basis in fact.

 

[Sonwatcher]

I have heard that an antenna with a high gain can in fact work against you . Some systems work better with less gain because it allows less directivity of the antenna. Higher gain means the antenna is more directional . Correct ?

 

[W5LZ]

Sonwatcher,
I'd say that was a very definite... maybe. Forget about 'gain' for a minute. Directional antennas can be a detriment because they may not be pointed in the 'right' direction. So, sure, you may miss something. Easiest answer is turn the antenna. The 'gain' that a typical directional antenna has is usually a 'plus' though, but you gotta point it right to realize that 'plus'.
Omnidirectional antennas can have 'gain' also. It typically means sort of flattening it's radiation pattern so that pattern sort of 'squishes' out further (hows that for a really 'tacky' way of saying it?). Vertical antennas can also be non-omni-directional. Usually means more than just one antenna, and phased. The same thing about where it's pointed applies to them too. (The old 'SuperScanner', for instance.)
So, gain can either work for you or against you, depending on how it's used. I sort of think that I wouldn't turn down having that gain, but am just not going way out of my way to get it either.
So, a definite maybe, sort of, kind'a.
- 'Doc

 

[Sonwatcher]

So, a definite maybe, sort of, kind'a.

Hee hee...I like that. LOL !

Thanks Doc !

 

[kor b]

kor b,
I'm afraid that 'quote' is just sooo wrong, in more than one way. I would suggest finding out just exactly what "propagation delay" and "velocity factor" mean. As evidenced by that 'quote', Mr Franklin didn't have a clue. Those two terms mean exactly the same thing, just being expressed/said differently, and used inappropriately in that 'quote'.
The reason a typical fiberglass 1/4 wave antenna is shorter than the typical 102" steel whip is because the copper conductor in that thing is wound around the fiberglass core, making it a helically wound, shortened/loaded, antenna. Of course it's shorter than a straight run of conductor!
There IS a difference in conductivity between copper and steel, copper being slightly more conductive than steel. That difference in conductivity just isn't that much, and will make very, very, very little difference to RF, if any practical difference at all. And since that steel whip has an average larger diameter than the copper wire in that fiberglass antenna, the steel whip should be shorter, not longer. Diameter of a conductor does make some difference, that's well documented, I see no reason to try proving it here (called 'skin-effect', by the way).
Having been familiar with Louis Franklin's work for quite a few years I think that's a mis-quote. He was smarter than that.
- 'Doc


And just for 'grins', both copper and steel, whether on, or wrapped in fiberglass, behave exactly the same way as antennas. Neither has any 'preference' for noise. That's another one of those 'myths', no basis in fact.

No its not a miss quote. I typed it stright from his book. And im sure he wasn't talking about the wound stick that you are referring to.

Page 22 The "Screwdriver Expert's" Guide Copyright 1977-1994

If that quote is wrong than so be it. But it is a acruate quote.

 

[W5LZ]

kor b,
I'm not, and wasn't, saying you misquoted, just that there is what I consider an obvious misquote. It certainly wouldn't be the first time a publisher, or the printer got it wrong. No idea where/how the 'goof' got there, but it is there.
- 'Doc

 

[hookedon6]

kor b,(edit for brevity)
I'm afraid that 'quote' is just sooo wrong, in more than one way...the reason a typical fiberglass 1/4 wave antenna is shorter than the typical 102" steel whip is because the copper conductor in that thing is wound around the fiberglass core.... Of course it's shorter....

i agree, there is more than one factor "in play" here. the major factor being the helically wound part.

food for thought,

i constructed a 6 element cubical quad and wanted it resonant at 50.125. i did all the proper calculations ( i thought) and after i constructed it, it was resonant slighty (about 2%) lower in the band. to correct it, i had two choices, to physically shorten the antenna wires or to remove the insulation on the wire. i stripped the insulation off and... bingo! 50.125.

perhaps, the fiberglass is also (slighty) acting as the insulation on my wire was.

question: are the 102 inch cb steel whips really "too short"? aren't they designed to always use a 6 inch spring.

 

[The Jerk]

question: are the 102 inch cb steel whips really "too short"? aren't they designed to always use a 6 inch spring.

The 102 is 102" long...the spring however is typically only about 4 inches long...

I believe they intend on the buyer using a ball mount with any 102, and that adds another few inches to the "electrical" length of the antenna. If you look at a ball mount, you will see there is several inches between the termination point of the coax (usually a ring terminal held by a screw) and the 3/8x24 antenna mounting point. Ball mounts are usually metal, and isolated (i.e. not grounded) from the body of the vehicle.

At least that's how I figured they got 108 inches out of a 102 inch whip and 4 inch spring.