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Would a big 'ole 'tenner really improve my reception here?


standingbear73

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Mobile antennas are designed to be 1/4 electrical wavelength. They are phsycially shortnend by the use of a coil. The old 102" "squirrel killer", is considered to be the ultimate antenna because it meets both criteria. Personally I would not want want either slapping against my paint job and I think tennis balls
look "tacky". I have not been CB mobiling for quite some time but try to keep up on it a little. I think if I were going to mount a antenna on the bumper I would check into if Firestick still makes their 6 foot top loaded whip. The coil is high enough to be above the roof line. The coil is larger in diameter than most antennas of this style. This will give you a lower SWR over a wider channel range. It will be somewhat directional following the longest path from antenna to vehicle. The K-40 will work well on the roof also.
.........................................................................................
RECEPTION?

You must have the only Explorer that does not emit an S-9 noise level from the fuel pump.
..........................................................................................
The bigger the antenna the more it hears.

Ya can't talk to'm if ya can't hear'm!
73,
Chuck
 


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jasonb

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i had always heard that the rear bumper is one of the worst spots to mount the antenna for reception. also, that the roof is the best.
 




CarFreak146

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Since I mostly do city driving, with clearances, I compromised and mounted my antenna right above the taillight.
 




Hokie

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Thats where I had it mounted but I was afraid that if the bracket ever got caught up off road it would bust the top of my tail light and/or damage my rear 1/4 panel and/or my rear hatch. I had it like this and had the antenna tucked up against the body and a tree snagged it pretty good. My mount on the bumper is sturdy as all hell and nothing's gonna hurt the bumper.
 




CarFreak146

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yeah I have that problem offroading with my current mount to.... b/c I have a fiberglass antenna also, but I think I'm gonna get rid of that one and get a steel whip and do the tennis ball bumper thing, so the whi[ will not damage the X when It get bumpy. :D
 




Hokie

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I really just want to put it on the roof, but then it would be annoying if i ever had to go to a parking garage. I guess I could just leave the antenna sitting in my truck and put it on when I go on the highway or when i'm off road
 




CarFreak146

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That'd be your best bet.
 




VAHAM

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Originally posted by Hokie


I didn't know that ground planes were as big of a deal for low powered radios (CB's). When doing UHF/VHF/low band police/emergency installs (I have 3 years in the communications installation biz), we only had problems with ground planes on 100W low band radios. Heck, most the time with CB's, we would just mount the antenna and call it a day since my boss didn't want me to mess with tuning them.

Thanks y'all! :chug:
That's because of the operating frequencies involved. A ground plane for 800mHz/UHF/VHF is physically much smaller than for low band (30-35 mHZ)

A quarter-wave on 440-450 is about 9", 19" for 150 mHz, approx 7' 9" for low-band vhf, and 102" for 27 mHz (CB). A quarter-wave vertical antenna requires a corresponding ground plane for reasonable propogation. The optimum ground plane would be to place the 1/4 wave antenna in the center of a sheet metal circle with a radius equivalent to the 1/4 wave antenna height.
That is not a problem on VHF/UHF, but physical constraints do start to appear as the operating freq. is lowered ( a 15-foot diameter circle on VHF-low, for example)
The radiation pattern is greatly distorted with anything less, and that is why on HF or on CB, the greatest signal strength is always in the direction of the greatest expanse of metal. In other word, antenna mou8nted at left rear corner puts strongest signal across right front headlight, as the electrical properties capitalize on achieving that 1/4 wavelength measurement. At the higher frequencies, near optimum ground planes are easily achievable, (only an 18" circle for UHF).
By the way, it is very rare to see 1/4 wave antennas on UHF public service... most are 1/2, 5/8 wavelength or longer, and dependency on the ground plane for the "missing half" is not critical.
IMHO,For what it's worth, get a decent balll mount and spring, and mount your 1/4 wave steel whip as high on the body (just up under the rear side window) on the drivers rear corner, then tie it down with a plactic clip to the luggage rack when going underground... The best "compromise" antenna you can get..
 




Hokie

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So a 102" steelie would be better than a 4' glass on the roof? I can't mount it on the side of the vehicle b/c I don't want to drill holes in the side. On top I have no problem with antenna holes. What about the top loaded 7' glass whips?

Thanks for your input guys!
 




VAHAM

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Well, in a word.. yes..

The steel whip mounted as high as possible on the side of the body still leaves 5 1/2'- 6'
of almost indestructable antenna in the clear above the roof line, and you are still radiating a physical 1/4 wavelength antenna.
The 4' whip on the top of the X is resonant via lumped inductance ( loaded top coil). Electrically, it may be a 1/4 wavelength, but physically, it is not, and you sacrifice signal strengh & efficency for smaller size.
If you are only worried about 1 or 2 mile communication range, typically the 4' antenna will work just fine.
My reply was to your original post asking if a big antenna works "better"-- and yes it does, if, by "better", you mean "will help you to communicate more effectively".
The 7' fiberglass antenna on the roof option tends to hit tree limbs, bank drive-throughs, fast food drive-throughs, etc, and the fiberglass will eventually split/shatter at the top exposing the conductor (wire) to the elements and to external damage.
If using a mag-mount on the roof, it better be a big one to support a 7' f'glass antenna- if using a permanant mount, you would still be smart to use a ball-mount for that size antenna, and there goes your parking garage scenario.
I understand your hesitance to make holes, but...... prioritys will lead you in the direction you must choose....
 




Hokie

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If I get a big whip, it'll be mounted at my bumper height on my 2"x1/4" steel bracket that I made. It bolts directly to the bumper and when I pull up on it, the whole truck comes up.. i'm sure its sturdy enough for a big 'ole whip.

the greatest signal strength is always in the direction of the greatest expanse of metal
Is this for Rx and Tx? I know my Tx is limited to only 4W so I'm really trying to get the best possible Rx (so I can hear where all the cops are on the interstate ~ gotta love channel 19!)

I'm really learning alot here guys. Thanks!
 




VAHAM

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Efficiency works both ways..... affecting both Rx and Tx.

On the bumper is a good solid mount.. a top-loaded fiberglass antenna that clears the roofline by a couple of feet will help cut down on the interaction between the steel body and the antenna, and will give you a better chance of getting your SWR down to reasonable levels.
It will not be as good as a higher-mounted 1/4 wave steel whip, but it will be less of a hassle and live a longer life than a 4' f'glass antenna on the roof.
I would still suggest putting a spring ( not a cheap Radio-Shack junk spring) between the antenna and the mount... it just might keep it from getting snapped off.
 




Hokie

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Thanks.. Now I just gotta find a shop that can get me a 7' Firestick KW since shipping a 7' antenna is pretty expensive.

Our local radio shack only has antenna springs that are like 2" Dia and 6" high, they look pretty sturdy.

That and gotta find a shop that will tune CB's. The local communications shop says they don't bother with CB's.. Maybe I can give em $5 to borrow a Bird watt meter and a 5W plug and some test cables. I can do the rest myself.
 




VAHAM

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You don't need a Bird... a 10.00 Rat Shack SWR bridge will work fine.
I don't know anyonw who has a 5-watt slug for a Bird or for a Coaxial Dynamics...

The physical properties of their springs aren't the problem... they are physically strong..... the problem is in the electrical properties after exposure to the rain and snow.. cheap materials.... corrosion becomes an insulator instead of a conductor... when that happens, only your coax is radiating, most of your signal goes right back into the final transistors of your radio, and POOF!. Once you let the magic smoke out, it won't work any more.

If you want to make a quick trip to Springfield after you have it all mounted, I'll help you tune the antenna- I think about 2 hours from C'ville-- 29N to 66 E to FFX CO Pkwy.
 




Hokie

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Originally posted by VAHAM
I don't know anyonw who has a 5-watt slug for a Bird or for a Coaxial Dynamics...
I do!

Clear Communications, Inc.
Owned by Steve Duncan

C'ville, Harrisonburg, Staunton

He has contracts for Charlottesville, Orange, Greene, Fluvanna, August, Waynesboro, etc. for fire/pd/ambulence etc. I did all types of installs but antennas were always mounted the same on cop cars (truck/roof)

I worked for em for 3 summers and 1 fall. Thats where I tuned my cb this summer when I had it mounted at my tailight. Just borrowed my old Bird meter and Steve's slug. 5 minutes later I was on the road :D
 




VAHAM

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Heck, then... you're halfway there !!!

I rarely mess with any Bird slugs less than 2.5Kw, and I don't tune antennas with a Bird, only monitor Power Out.
For antenna tuning, you can't beat my antenna analyzer... indicates SWR, resonant frequency, and resistance all in one shot... not just the SWR.

Good luck !
CLH
 




VAHAM

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Sandy

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:cool:

Are you talking about tuning the antenna to teh system or tuning the CB.

If you are talking about the CB, unless you have a need to have it tuned, i.e. powering something else, there is not need to tune it.
To make any difference you would need to increase the output power by three or four times and to try and tune the modulation circuit will only cause more distorsion (sp).
Unless you plan to install more power final and redo the other circuits that are effected, i.e. more filtering for the increase distorsion, the best bet is to leave a stock CB where it is.

If you are just trying to talk to the vehicle next to you on the trail or maybe the other side of town, then a stock CB with a Noise Canceling Power Microphone would work OK.

Luck on your choise,
 


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Hokie

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Huh? I thought aftermarket 'tuning' of CBs was illegal? I am talking about tuning the antenna for the system, ie SWR or reflected power.
 




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