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cb antenna in stock location

Bmxpunk1369

NAXJA Forum User
Location
Bridgewater, NJ
Is there any way to set up a stainless 3 ft whip in the radio antenna location and run both the radio and the cb off that one antenna (not at the same time of course). Could i just pull that mount out, run the coaxial to that spot, hook up the antenna to both the coaxial and the am/fm lines and then put it all back together and have it work alright.
 
I doubt it. A short stainless whip has a coil load in it to make up for it's shortness. You could put one there for your cb but I doubt you could get good radio[AM/FM] reception off it. I'm shure the Impedence [ a type of resistence] load would be to high for the radio {AM/FM]. I think a radio recever needs no resistence to work correctly.
 
There is an adapter you can buy, I had one but lost it or I would give it to you, it sets up your antenna as a dual use antenna, works like the garbage it is, definitely worth having the second seperate antenna.
 
jeepin_al said:
There is an adapter you can buy, I had one but lost it or I would give it to you, it sets up your antenna as a dual use antenna, works like the garbage it is, definitely worth having the second seperate antenna.

That adapter is garbage, and will probably result in a burned up transmitter in your CB.

The 3-way type I mentioned - make sure it is TUNEABLE!!!
[edit] Here is an example:
40_1_b.JPG

88_1.JPG
 
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scoobyxj said:
... A short stainless whip has a coil load in it to make up for it's shortness.

In a nutshell, yes, but it's much more complicated...

scoobyxj said:
You could put one there for your cb but I doubt you could get good radio[AM/FM] reception off it. I'm shure the Impedence [ a type of resistence] load would be to high for the radio {AM/FM]. I think a radio recever needs no resistence to work correctly.

Impedance is complex i.e.: Z=R+-jX

It is a "type" of resistance, but inductive and capacitive reactance are the "y" values, thus have a far greater bearing than pure resistance. For any of this to happen, there must be "power", i.e: ohm's law...

Radiator (antenna) reactance is a function of frequency.

All of the above is important to what the final RF amplifier (power) in a transmitter "sees".

A reciever has no such stage, hence, antenna impedance will not in any way affect the reciever from a operational perspective.

So...

You can use your CB antenna for AM/FM, and quite effectively too.

The trick is to use a good grounded antenna switch that makes use of PL-259 connectors. This is what you see on the "radio" end of your CB antenna coax. You'll need a PL-259 and an adapter for the usually smaller 75 ohm coax for your AM/FM. A double PL type patch coax for your CB, and you'll be set.

You'll only be able to use one at any given time. Do not under any circumstances try to "splice" your CB and AM/FM into one coax, or, as they say, "that'll be all she wrote", for both of them...

--ron
 
Twisted Copper said:
Absolutely you can. It is called a 3-way antenna (AM/FM/CB) and they are out there. Most will have an adjustment screw at the top to trim SWR's.

Is this hooked up to both the CB and the AM/FM at the same time? If so, it's news to me.

It looks to be an antenna advertised to "work" for AM/FM/CB, which is entirely possible to do, although not all at the same time...

In my experience, and actually measuring antennas with an analyzer, the little "tuning" extensions on the end of "Firesticks" and the like are absolutely worthless for obtaining any reasonable match in 99% of all vehicle installations.

The hacksaw is your friend...

I'd buy the best matching antenna and installation for the CB, your AM/FM performance will be just as good as stock, or better, via an antenna switch.

--ron

PS: Kinda nitpicky I'm sure, but SWR is always in singular. The image of plural will lead to madness for most radio geeks...
 
Captain Ron said:
... Impedance is complex i.e.: Z=R+-jX ...

Clarification:

j (imaginary, but in this case, 90 degrees out of phase, or the vertical scale...) is used in place of i (current) for electronics, sorry.

Ohm's law for Impedance: E=I Z, etc...

--ron
 
Thanks Captan Ron that is a good explanation of impeadence. I took two years of electronics in highschool, but that's been 7/8 years a go. Without regular use I have forgotten most of it, and have to look up most stuff when I need it. I knew of the special antennas/converter boxes, but I have always been under the inpression that they where junk, and they where not good for your CB radio. I didn't know that the tuning screws on the end of antennas where not as good as a desgine where you would clip the wire, but I can see the lesser degree of tunability. I have alwas been told that a full length whip is the best. Would you agree, or not. I have 4ft Firestick fiberglass whip on now. I did have a full length SS whip, and spring, but it kept hitting on the side of the hatch. I took the spring off, and it wasn't as bad but the base broke from not having enough flex. So I got the Firestick, and put the spring back on to give it the height it needed to be far enough over the roof, and to keep the local drivethru car wash from breaking it off.
 
A 5/8 or 1/4 wave whip is by far superior to any "compromise" antenna, such as a base loaded coil, but, it's not with out it's own problems.

Mounting location becomes very, very critical, for correct feedpoint impedance. Bandwidth is another problem.

For reference: Length (ft) = 234/f(MHz) For quarter wave. This includes a reasonable "K" for conductor thickness

CB = 26.965-27.405 Mhz, Channel 14 is 27.125 MHz

A quarter wave vertical would be: 234/27.125 = 8.63 ft

Bandwidth is usually thought of as SWR across the band. You can have a perfect 1:1 match at, say channel 4, but at channel 24, the SWR will be drastically different.

Full wave will not yield anywhere near a required feedpoint impedance (usually 50 ohms) in a vertical. So, no, generally the long whips are not as efficient.

Lastly, believe it or not, base loading is the least desirable way to impedance match, much contrary to the popularity of the Wilson line. If you work out the math, you'll see that most of the RF current is in the coil, not the element, where you want it.

Top loading is king...

--ron
 
Captain Ron said:
Is this hooked up to both the CB and the AM/FM at the same time? If so, it's news to me.

It looks to be an antenna advertised to "work" for AM/FM/CB, which is entirely possible to do, although not all at the same time...

In my experience, and actually measuring antennas with an analyzer, the little "tuning" extensions on the end of "Firesticks" and the like are absolutely worthless for obtaining any reasonable match in 99% of all vehicle installations.

The hacksaw is your friend...

I'd buy the best matching antenna and installation for the CB, your AM/FM performance will be just as good as stock, or better, via an antenna switch.

--ron

PS: Kinda nitpicky I'm sure, but SWR is always in singular. The image of plural will lead to madness for most radio geeks...

Sorry for the late reply. Yes they will work at the same time. When I was in college I worked at a 12V (Car audio, security, CB's, etc) shop. We were the only place in Bel Air, MD that you could get a decent CB setup. We installed CB's on everything from 18 Wheelers to boats. I do know for a fact that those 3 way antennas both work and tune well (if properly grounded). They won't perform like a 102" whip but they did work and the only time we ever had anyone return with a problem was some yahoo running a linear amplifier (which was illegal). I was never into CB's but I learned quite a bit about them. I'm no electrical engineer but I can tell you for sure they work.
 
Figured I would revive this older thread...Cuz I just did this. I drilled the stock antenna mount and fabbed my own "Stud Mount" so far seems to work great I will get it tuned this week. I am relocating the FM/AM antenna to above the mirror or under the front of the headliner. I am running a 4' k40 whip

Much better then dilling holes in the tailgate I think and I still have the option to do so for the 2 meter antenna that is comming later.
 
Sting - What kind of anntena are you using for your AM/FM? Can you snap pics what you are doing? I'd be most interested!
 
I actualy have done nothing about the FM yet I am looking at 2 different options for the radio It will not be as good as the vertical but very very ok for my needs. I have just cut the antenna wire at the fender for now and still get 1/2 of my stations while in the city. but have bad reception as soon as I leave town. I listen to MP3s mostly anyway though. These are the antennas I am looking at. I will snap some pictures tomorrow of my modified mount, I want to make a few changes to it.

http://www.ecshylites.citymax.com/page/page/761353.htm

http://www.restoremustangs.com/HiddenAntenna-248.html

http://cgi.ebay.com/ebaymotors/Custom-Auto-Sounds-Hidden-Antenna-New_W0QQitemZ230086366596QQihZ013QQcategoryZ38636QQcmdZViewItem
 
Drilling holes in the rear hatch to mount an antenna from is a waste of time because the rear hatch if made of fiberglass and will not provide the proper ground.
 
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