| Author |
Message |
    
Scoobydoo
Member
Username: Scoobydoo
Post Number: 67
Registered: 8-2005
| | Posted on Thursday, February 16, 2006 - 4:42 pm: | 
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Ok, using an Antenna length calculator, A quarter wave whip must be 103.2 inches long to be centered on channel 20. My whips is 102.75 plus the stud mount mount which makes it 103.75. Do I include the stud in the measurement? Right now my SWR's are lower on 40 then 1 which would mean I need to lengthen the antenna. Does where I have the antenna mounted and how good the ground plane is, effect the length? I have a heavy duty 4.5" inch spring I can add to it. Thanks for any help. |
Kj7gs
Junior Member
Username: Kj7gs
Post Number: 42
Registered: 12-2004
| | Posted on Friday, February 17, 2006 - 1:22 am: |
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Doing my own calculations for the band center of Ch 19, I came up with 103.3 which is going to send me back to my own 9' whip to see if it really is 9' or 102" or at the calculated length. I suppose it just won't make a whole lot of difference anyway, the thing is pretty broadbanded if I'm not mistaken.
I'm a fan of placement myself. I read an article once describing the job of radials as cancelling out return currents, and placing an antenna at the edge of a metal plane would simply make it into a funny-looking dipole, meaning radiation coming from the vehicle in addition to the antenna -- and sorta "affecting the length" by making your 1/4-wave no longer a 1/4 wave configuration, more like an OCF L-shaped dipole. And "how good the ground plane is" does kind of the same thing. You want canceled return currents so that only the antenna radiates.
I mounted my Outbacker straight up on the roof edge rail of my RV, and it had a terrible SWR. Put it at a 45-degree angle and SWR was brought to acceptable levels because of the new GP that it had. |
Scoobydoo
Member
Username: Scoobydoo
Post Number: 69
Registered: 8-2005
| | Posted on Saturday, February 18, 2006 - 1:22 am: |
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I went ahead and tried the spring and it made the swrs more consistant across the 40, still slightly higher on 1. My length with spring right now is 107.25 inches. Antenna by itself is 102.75. My antenna is mounted on the right side of my truck about 8 inches away from the cab. Probably has a very odd pattern being there. |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1093
Registered: 6-2004
| | Posted on Saturday, February 18, 2006 - 10:52 pm: |
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When you did your calculations, what formula did you use? Does it take into consideration the resistance of the whip's formulation of stainless steel? How did you compensate for the taper of the whip or did you just assume it to be a simple conical form? Did you factor in the tip's shape and size?
I wouldn't worry about the length of the whip, I'd worry more about the VSWR and how it's loading your transmitter. |
Kmt36264
New member
Username: Kmt36264
Post Number: 9
Registered: 1-2006
| | Posted on Monday, February 20, 2006 - 12:04 am: |
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I have made some adapters to replace the 3/8x24 that are 1" long. I made some from 3/4" alum. rod in sizes ranging from 2"-6" so i can get the best match. Usually the whip is broadbanded enough, but is you are a stickler like me, then this is a pretty good way to go. Depending how the antenna is mounted, the length is usually effectively shortened. Using a little longer coupling can help. If you can get some 3/8x24 threaded rod or studs, you can add one or two more couplings as well.
Does anyone know if there is anywhere to get a thicker, stiffer 102"? (seriously, no viagra jokes please) |
Georgeodjungle
Junior Member
Username: Georgeodjungle
Post Number: 37
Registered: 1-2006
| | Posted on Monday, February 20, 2006 - 12:14 pm: |
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a "zing ring" with no spring will give your whip a more even pattern.
plus a bit more gain.
& more broad banded.
we make them with a 3'hunk of wire or brazing rod & a hose clamp.
no extensions needed.
but if you want them you can find them in the with the unistrut & all thread stuff.
you can find heavy duty whips @ military surplus.
you'll have to cut it down like 16" or so.
but even when the whip is bent over like 20 degrees,motoring down the road, still will out perform any other antenna out there.
the zing ring will fix that too.
whips rule. |
Marconi
Advanced Member
Username: Marconi
Post Number: 600
Registered: 11-2001
| | Posted on Monday, February 20, 2006 - 2:22 pm: |
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george you may be able to see a more broad banded characteristic by testing, but how do you see a better pattern and more gain?
Also, I was under the impression that within reason, you cannot have both max gain and max bandwidth at the same time. Doesn't your idea defy this known rule in optomizing of any antenna? |
Georgeodjungle
Junior Member
Username: Georgeodjungle
Post Number: 38
Registered: 1-2006
| | Posted on Monday, February 20, 2006 - 5:19 pm: |
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we use a field strength meter,& radio checks from same stations about the same time well as long as it takes to swap antennas.
& as far as bandwidth we use a swr meter.
i think your right about "optomizing" but that applies to 1/2 wave and larger."actual size"
not to mobiles.
1/4 wave "actual size" and smaller we see improvements.
try it out...
hopes this helps ya get out...
p.s.
when you use fs meter.
there realy easy to make.
park on snow, mud, durt or sand.
walk around the moble keeping meter at the same reading.
your foot tracks will give you your pattern.
some folks can't walk draging a foot & looking at a meter.
add chewing gumm and have fun. |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1105
Registered: 6-2004
| | Posted on Saturday, February 25, 2006 - 8:17 pm: |
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A zing ring? LOL Time to whip out my favorite quote - "You cannot be serious!"
First - If it's attached to the radiator per the installation instructions, then how does it accomplish a ground plane?
Second - It's about a foot in diameter. How does it accomplish any type of useful ground plane for 27 MHz at that size?
Those things are just more chrome for truckers to doll up their rigs. They accomplish absolutely nothing positive, and on the negative side they probably cause more ground loss. |
Georgeodjungle
Junior Member
Username: Georgeodjungle
Post Number: 39
Registered: 1-2006
| | Posted on Saturday, February 25, 2006 - 10:01 pm: |
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obviousy haven't tried it.
o.k. o.k. this is a fourm for learning.
first:
thay call it a "primary ground plane"
i don't know about that, call it what ever,
455s new dealy, but it does make it more of an onmi pattern.
that means rounded.
even mounted on the side or bumper.
and the fs meter & raido checks mention before bla bla bla...
second:
it's 4" to 8" what ever works best.
i should try a one foot one see what happens.
you might have come up with some thing.
the store bought one is like 5".
&:
chrome? ya, chrome, that will look pretty.
works in this world, for us...
"probably" there's your out.
you haven't tried it. |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1107
Registered: 6-2004
| | Posted on Saturday, February 25, 2006 - 11:40 pm: |
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I don't pretend to understand the physics involved in antenna design, but everything I do know tells me that a zing ring is just a way to separate a trucker from his money and nothing more.
I also know that a hand held field strength meter isn't a precision instrument, and you can't measure gain with radio checks. |
Rldrake
Member
Username: Rldrake
Post Number: 95
Registered: 1-2006
| | Posted on Sunday, February 26, 2006 - 4:30 am: |
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The best "gain" a 1/4 wave whip can achieve is
0 dbd (unity gain). The only thing that can affect the "pattern" is where the antenna is mounted on the vehicle. A mount in the center of the roof would come closest to producing a omni-directional pattern...but it still wouldn't be omni-directional because the roof isn't wide enough (at 27mhz)...major lobes would be to the front and rear. The only way to get a real omni-directional pattern would be to use a horizontally polarized "halo" antenna mounted high enough not to be skewed by the vehicle's body. Since almost all the other CBers, by convention, use vertical polarization such an antenna wouldn't be very effective. A halo, at best, is also a unity gain antenna.
The "zing ring" sort of sounds like a capacity hat...but would need to be much larger and mounted at the top of the antenna to accomplish much of anything other than to allow additional wind drag. |
Kj7gs
Junior Member
Username: Kj7gs
Post Number: 43
Registered: 12-2004
| | Posted on Wednesday, March 01, 2006 - 3:42 am: |
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I don't think symmetry is all that much of an issue in giving you an omnidirectional pattern. You're looking for cancelling of return currents, and centrally locating a 1/4 wave antenna on a typical vehical body will accomplish that, even if the ground plane is a rectangular shape. Still can't get a visual on a "halo" -- would it look something like a Ringo Ranger? |
Rldrake
Member
Username: Rldrake
Post Number: 98
Registered: 1-2006
| | Posted on Thursday, March 02, 2006 - 2:49 am: |
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The "ringos" are verticals. The old "halos" were usualy one to three rings, no "whip" to them. Some are square shaped or triangle shaped.
If the "ringo" you refer to is what I think it is...it would actually be a slight variation of a J-pole antenna (a 1/2 wave end fed vertical).
Try google search on Par's "omni-angles" (triangle shaped) and M2's "HO Loop" (square shapeped) antennas. Might also research MFJ's little hf "magnetic loop".
Their illustrations will give you better understanding...You have probably seen lots of them around without even realizing what they were.
Also examples of the little loops, or halos, are usually in about any book on basic antennas, most amateur radio catalogs, and websites.
Kind of like the little uhf loops that used to come with portable TV sets...only larger and beefier.
Avanti used to make one years's ago that attached to a vehicles's roof with suction cups and strap...kind of looked like a luggage rack. Some people seemed to like those, but I can't see how they could have been very useful...they mounted way to close to the roof. |
Wheelco505
Junior Member
Username: Wheelco505
Post Number: 42
Registered: 12-2004
| | Posted on Thursday, March 02, 2006 - 12:31 pm: |
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Rldrake if you go to the signal engineering web site,you'll see that they make a halo for 27 mhz and it is quite good 505 |
Rldrake
Intermediate Member
Username: Rldrake
Post Number: 100
Registered: 1-2006
| | Posted on Thursday, March 02, 2006 - 7:04 pm: |
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Thanks,505.
That model 45 is a design that I haven't seen.
Their yagis and other antennas look to be well built and engineered.
Very interesting. |
Bruce
Senior Member
Username: Bruce
Post Number: 3604
Registered: 9-2003
| | Posted on Thursday, March 02, 2006 - 7:27 pm: |
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This place makes SQUAILOS which are square hailos
www . ku4ab . com |
