Different Look At 102" Whip Discussion

towerdog said:

I dont think a 1/4 whip is often the best option for a CB antenna. Mounting it below metal, like on a bumper screws up radiation and swr. When driving 70 mpg and the top of it is leaning horizontal or bent like a u, i think thats a problem as well.

In theory a "102" whip would be better, and if you could mount it center of the roof, and find a whip stiff enough not to flop so much in the wind it would be better..but who the hell wants to put a hole in their roof besides me.

I would take a good base or center loaded whip on the roof over a "102" on the side or bumper.

I run a "102" on my truck, with 4 or 5 inch spring, mounted just forward of the tailgate, on the side of the bed. It just worked, had better luck with a K40 mag mount. SWR was not too bad for the lack of counterpose, about 1.3:1 on commercial grade meter. 1.3:1 at about 26.5mhz, more like 1.5:1 at 27.2, i just never got around to cutting it down as i dont really drive the truck anymore.

They need the spring on CB, and then cut down to work right.

Click to expand...

Towerdog, I never had such bad issues using a 102" whip, but there is no question it is not always the best. Even thought theory might suggest a small advantage over many other shorter mobile CB antennas, we repeatedly hear stories about how bad the whip works.

I never used a spring, but plenty of guys did, and they seemed to work fine also. When the sideband radios came out I went that way and we mostly talked a little higher in frequency, but my whip antenna always seemed to be so broadbanded...that it was hard to tell any difference plus we didn't have all the frequencies available we have today.

I heard lots of CB talk back in those days kind of like your claims, but I was never convinced of all the issues banded about.

I mostly ran a whip mounted on an all metal rear bumper of my pickup trucks over the years. Maybe I was just didn't realize I was missing out. IMO, those bumpers were real bumpers, not the pretty stuff like used today. When I tried a couple of mag mounts on the roof or the hood, I though I had good results as well. I think back in the days 60's - 80' the trucks seemed to be put together better with welded seams, not using a lot of non-conductive adhesives like is probably done today.

I gave up mobile operations in the early 90's and never looked back and I never fell for any of those high dollar big coil jobbers either. I'm too old now to work with my antennas, but I can still use my 102" whips to build my Marconi...like noted in my profile image above. Of course the whips are not shown, but I'll leave that to your imagination. That antenna works as good as any of the other bigger antennas I have to talk on, and I have several.

The 1/4 wave SS whip with spring on my rear bumper on my Chevy truck was like a beam antenna. Good 20 mile range off the opposite front corner and good FB. Plus I had my R/S antenna clip made out of nylon to stow the antenna in case if low structures.

I found this on 108" whip SWR by The DB. Can't wait til I get my ARRL antenna handbook so I get eliminate any erroneous beliefs I have about antennas.
Quote from 108" whip SWR thread:"246 / 27.185Mhz = 9.049... feet

246 is from the ARRL antenna book for finding the length of quarter wave antennas in feet
27.185Mhz is the middle frequency in the CB band

9.049... feet is just over 108 inches.

246 / 29.0Mhz = 8.482... feet

29.0Mhz is close to the middle of the 10 meter ham band

8.482... feet is just under 102 inches

As you can see the length of the 102" whip is not in the CB band, which is why a spring/riser i said to be needed.

These calculation did not calculate width as the width of a 102" whip is not significant enough to matter.

Quote:
Originally Posted by Brake Weight
I get better meter readings in my truck without the spring.
Readings with just an SWR meter or an Antenna Analyzer?


The DB"
W5LZ used a different number

Lil'Yeshua said:

I found this on 108" whip SWR by The DB. Can't wait til I get my ARRL antenna handbook so I get eliminate any erroneous beliefs I have about antennas.
Quote from 108" whip SWR thread:"246 / 27.185Mhz = 9.049... feet

246 is from the ARRL antenna book for finding the length of quarter wave antennas in feet
27.185Mhz is the middle frequency in the CB band

9.049... feet is just over 108 inches.

246 / 29.0Mhz = 8.482... feet

29.0Mhz is close to the middle of the 10 meter ham band

8.482... feet is just under 102 inches

As you can see the length of the 102" whip is not in the CB band, which is why a spring/riser i said to be needed.

These calculation did not calculate width as the width of a 102" whip is not significant enough to matter.

Quote:
Originally Posted by Brake Weight
I get better meter readings in my truck without the spring.
Readings with just an SWR meter or an Antenna Analyzer?


The DB"
W5LZ used a different number

Click to expand...

I remember that. My numbers (divide frequency from 246) were based on the full quarter wavelength.

Doc essentially started with 246 and multiplied that by 'K' which in this case is 0.95, which is meant to modify calculation to account for width, and got 234. He then divided the frequency from that.

The width for that factor 'K' is for a half inch diameter antenna at cb frequencies. I have yet to see a 102" whip that is a full half inch diameter all of the way up, and rarely more than an inch at the bottom where it connects to its mount has more than half of that diameter, therefore the actual length is somewhere in between those two figures.

There is also the fact that I prefer to error on the side of a little more length over the other direction. For some reason it is typically easier to make an antenna shorter than longer... Go figure... Although I guess with a 102" whip you can simply add a spring or a riser to the base to make it a little longer if need be...

When you get your book pages 2-3 to 2-5 covers antenna diameter.


The DB

I always used 468 or 234 for 1/4wl but its not really an accurate formula. I remember reading an article somewhere that went into the details and I coulnt make sense of it, but the point was divide by 234 or something close and add some inches then check and cut it with a meter.

and I never said 102" whip was bad, in an ideal setup it in theory will outpreform anyy K40, Wilson or big coil thing, at least for power radiated into the sky, although not by much over a Wilson 5/8 loaded. I have heard some debate over whether or not there is such a thing as a 5/8WL base loaded mobile antenna, but running high power in theory would be better for local work.

To heck with a 102 whip...I run a 108 whip from MFJ....no need for a coil spring, and the antenna still lays over at highway speeds, but pops back up when I stop. Couple it with a nice 4 pill amp and I have no problem causing my own pile ups on the air.

and I never said 102" whip was bad, in an ideal setup it in theory will outpreform anyy K40, Wilson or big coil thing, at least for power radiated into the sky, although not by much over a Wilson 5/8 loaded. I have heard some debate over whether or not there is such a thing as a 5/8WL base loaded mobile antenna, but running high power in theory would be better for local work.

Turbo T said:

To heck with a 102 whip...I run a 108 whip from MFJ....no need for a coil spring, and the antenna still lays over at highway speeds, but pops back up when I stop. Couple it with a nice 4 pill amp and I have no problem causing my own pile ups on the air.

Click to expand...

How much was shipping for the 108"?
P.S. My Sirio Performer PL-5000 is the closest thing to a 102". It's practically the same height as a bumper mounted 102" and it's mounted on the roof. Only thing is that my mini SUV doesn't provide much sheet metal hence the 70 centimeters I cut off of it to make it work on 11 meters,particularly on the upper portion of 11 meters.
http://www.automobilemag.com/am/2004/chevrolet/tracker/specifications.html

towerdog said:

and I never said 102" whip was bad, in an ideal setup it in theory will outpreform anyy K40, Wilson or big coil thing, at least for power radiated into the sky, although not by much over a Wilson 5/8 loaded. I have heard some debate over whether or not there is such a thing as a 5/8WL base loaded mobile antenna, but running high power in theory would be better for local work.

Click to expand...

The mobile antennas listed as "5/8 wavelength" antennas are not really 5/8 wavelength. What they do is use a 5/8 of an electrical wavelength of wire to make the antenna, but the antenna itself is mostly coiled up in what is typically a 4 or 5 foot length. The pattern the antenna produces is based on its physical length, not its electrical length.

Long story short, no matter what they claim, a 4 foot antenna radiates like a 4 foot antenna, and nothing they say will change that. All saying it is a "5/8 wavelength" is in reality is marketing. You don't get the benefits of the 5/8 wavelength antenna unless you have the full physical length.

A perfect example of this effect is in the typical mobile CB antennas. You have a 1/4 wavelength whip (near 102" long) and you have the cheap $15 Walmart antenna. They are both an electrical 1/4 wavelength, but which one is better... Hint, the physical length tells the tale...


The DB

Sometimes discussing numbers can be interesting, but in this case what is the point, when at the very best about all we can do is get close to resonance at some desired frequency, and then tune our antenna if we're able and find it necessary?

Like Jazzsinger recently told us...about the best antenna out there that will get us very close to the magic numbers for a perfect match is the Starduster design, and then you guys want to talk about a mobile setup that is fraught with a potentially very bad ground plane design.

With all the issues associated with a mobile setups, one will just be lucky if a calculated resonant length can be calculated using one of these whizzbang number crunchers...you guys refer to on the Internet and apply it to your mobile.

You boys can check below for the bandwidth curve I posted earlier in this thread of my Marconi using all 102" whips for the radiator and the radials, and you'll see the math is close enough to tell us the resonance should be about 27.500 mhz, give or take a few khz. Somebody posted that fact here too. Just using your radio and a meter, you are not likely to be able to tell the difference if you were working in the middle of the CB frequencies or at the upper or lower ends of the workable bandwidth. Plus in the real world that could change a little bit more, but again not as you would likely notice just working your radio.

http://www.worldwidedx.com/cb-antennas/135509-different-look-102-whip-discussion-6.html#post429782

When you guys end up with a good SD'r design using 102" whips you'll easily have a workable bandwidth from about 26.700 to 28.000 mhz. With such a setup you can barely see anything but a straight bandwidth curve and that is what my report indicates...so what is the point?

Say nothing about the 100's of variables that can effect resonance in pretty small ways. If you ain't playing a violin or a piano, then such small difference don't really matter.

I'd like to know where the formula is for this coil and how it is working.
Think that would be interesting to find out and possible use in the future . . .

I might have breezed by it in the ARRL Antenna Handbook
Nope. It covers VHF and UHF mobile antennas. Excuse me.

I might have breezed by it in the ARRL Antenna Handbook

Click to expand...

The reason for using an RF Choke is to limit certain freq that it is passing.
So; is it tuned for just passing ~27mhz; or removing it?

That pic came from this or not.
Antenna Matching