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  #16  
Old 04-11-2011, 10:53 AM
FireRanger FireRanger is offline
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Default Re: cb and antenna mounting.

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Originally Posted by icicle View Post
Unless you are running serious power co phase is a waste of time.
Completely untrue. Cophasing has nothing to do with power.
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  #17  
Old 04-11-2011, 10:58 AM
DiabloBlanco DiabloBlanco is offline
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Default Re: cb and antenna mounting.

Better gain. thats all you get.
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  #18  
Old 04-11-2011, 11:26 AM
FireRanger FireRanger is offline
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Default Re: cb and antenna mounting.

Cophasing, when done properly can add an additional 3db of directional gain to the front and back of the vehicle. 3dB is a lot when it comes to RF. That doubles your effective radiated power on transmit to the front and back, and will improve received signal quality from the front and back as well.

However, as stated, it does zilch unless you have the antennas 8ft apart.
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  #19  
Old 04-11-2011, 07:14 PM
Yogi Yogi is offline
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Default Re: cb and antenna mounting.

from what i,ve read- co-phase will work if your coax is 18' long. making up the differance in separation of antenna's. make sure you do not coil the excess cable. I'm thinking of running about 50 watts without an amp. so to recap--- 2 firestiks with 18' cophase coax (that I already have from a past truck) about 4.5' apart-pushing 50 watts. basiclly all i need are the antenna's. I have 2 center load 7-8' whips. I could use but I like the easy swr tune of the firestik.
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Last edited by Yogi; 04-11-2011 at 07:30 PM.
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Old 04-11-2011, 07:30 PM
FireRanger FireRanger is offline
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Default Re: cb and antenna mounting.

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Originally Posted by Yogi View Post
from what i,ve read- co-phase will work if your coax is 18' long. making up the differance in separation of antenna's. make sure you do not coil the excess cable.
What you've read is incorrect, or you've misinterpreted it. Coax length to each antenna is critical and 18ft is bullshit. It depends on the setup, the antennas, and the type of coax. The antennas need to be 8ft apart for it to work regardless. You can not make up for either by doing something else.
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  #21  
Old 04-11-2011, 11:51 PM
icicle icicle is offline
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Default Re: cb and antenna mounting.

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Originally Posted by FireRanger View Post
Completely untrue. Cophasing has nothing to do with power.
Okay are you so sure about that?
With power comes heat, I should know I have melted a couple of cheap antennas
Quote:
One additional reason has to do with power. Stock CB's leave the factory with the transmitter power limited to 4 watts but there is an underground market of linear amplifiers in existence. Inasmuch as power will eventually turn into heat, and the antenna will be required to dissipate that heat, two antennas will more than double the heat dissipation abilities of a single antenna.
Taken from Firestik's webside found below:
CHOOSING SINGLE OR CO-PHASE ANTENNA SYSTEM

Quote:
Originally Posted by FireRanger View Post
What you've read is incorrect, or you've misinterpreted it. Coax length to each antenna is critical and 18ft is bullshit. It depends on the setup, the antennas, and the type of coax. The antennas need to be 8ft apart for it to work regardless. You can not make up for either by doing something else.
So are you claiming Firestik info as B/S, if so you may not know what you are talking about.
Quote:
20. If your ground plane is good, your mount grounded and, your antenna favorably located, coax length rarely becomes an issue. But, if one or more mismatches occur, you may find high SWR. This can often be corrected by using 18 feet lengths of high quality coax.
this can be found here
Things Every CB'er Should Know

Last edited by icicle; 04-12-2011 at 12:19 AM. Reason: Added too.
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  #22  
Old 04-12-2011, 02:23 AM
FireRanger FireRanger is offline
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Default Re: cb and antenna mounting.

Uh, none of what you have quoted has anything to do with what you said. And yes, I'm sure about that. You said co-phasing is only useful if you are running a lot of power. That is not true and nothing you just posted indicates otherwise. What you posted about heat dissipation isn't the only or the primary reason to use a cophased setup. The benefits of proper cophasing occur regardless of your radio's power output. Cophasing applies directional GAIN which is completely unrelated to the power output of the radio. A stock 4 watt radio will see the same benefit as a 2kw illegal amplifier setup. Power is not a factor.

And yes, I am claiming firestick's info is BS regarding that magical 18ft of coax. The amount of complete utter bullshit on the internet from self-proclaimed CB radio experts is enormous. And this magical 18ft thing is one of the biggest loads of BS out there.
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  #23  
Old 04-12-2011, 08:51 AM
icicle icicle is offline
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Default Re: cb and antenna mounting.

You do realize that different Antennas are rated for so much.

Funny that Wilson also supports the 18' rule.
K40 also recommends 18', but does admit that one can use less like 9', 12', 15' as long as its in 3' steps.
Francis, We highly recommend using 18' coax cables for CB antenna installation. Use of 9' coax cables will mismatch your antenna causing high SWR.

So why is it so hard for you to accept this?
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  #24  
Old 04-12-2011, 09:18 AM
FireRanger FireRanger is offline
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Default Re: cb and antenna mounting.

Quote:
Originally Posted by icicle View Post
You do realize that different Antennas are rated for so much.
Also completely irrelevant and has nothing to do with your incorrect claim. Let me try to lay this out again. You said cophasing is only useful when you are using a lot of power. This is wrong. The primary benefit of cophasing is RF Gain which is completely independent of power output. A stock 4 watt radio will see the same RF gain as a 2kw amplifier or a 1 watt portable radio hooked up to it the coax. Nothing you post will change that.


Quote:
Originally Posted by icicle View Post
Funny that Wilson also supports the 18' rule.
K40 also recommends 18', but does admit that one can use less like 9', 12', 15' as long as its in 3' steps.
Francis, We highly recommend using 18' coax cables for CB antenna installation. Use of 9' coax cables will mismatch your antenna causing high SWR.
Yep. And it is still a bunch of bullshit being purported by cb radio experts. It doesn't work like that. First of all, your coax from the split to each antenna needs to be 75ohm coax, not standard 50ohm. Second, you need to use odd multiples of a 1/4 wavelength for each length of coax after the split. Third, to actually know the 1/4 wavelength, you need to calculate in the velocity factor of the type of coax you are using. Wavelength in cable is not a fixed number, it varies with the cable's velocity factor. So a 1/4 wavelength of RG59 is not the same as RG59 foam and is not the same as RG8 or as RG6 or anything else. Once you calculate the true 1/4 wavelength of the 75ohm coax, you can cut the cables to that length. It might be ~18. It might be ~21. It might be ~14. The mythical 18ft rule is and always has been, bullshit.

Quote:
Originally Posted by icicle View Post
So why is it so hard for you to accept this?
Because it's bullshit.
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Last edited by FireRanger; 04-12-2011 at 09:35 AM.
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  #25  
Old 04-12-2011, 09:57 AM
icicle icicle is offline
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Default Re: cb and antenna mounting.

Show me links to support this.

Without proof I still say it all BS
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  #26  
Old 04-12-2011, 11:48 AM
FireRanger FireRanger is offline
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Default Re: cb and antenna mounting.

Proof of which? I assume you mean coax cable length since you keep completely ignoring the fact that RF gain is the primary benefit of cophased arrays and do not wish to hear about it.

I've been a licensed ham radio operator for 12 years and doing professional life safety and radio dispatch system design for 10. I know the formulas and the science behind it. If you want to read about it from someone besides me because you think all of what I'm about to say is a lie, knock yourself out. I'm sure google will explain it all to you the same. And not from a manufacturers page, who is trying to sell you a product.

In the sky, Wavelength = 984 / Mhz.

In coaxial cable, you have to factor in the velocity factor. This is how fast RF travels down the coax, which changes the wavelength while it is in the coax. Velocity factor is a known value for each type of coaxial cable, because it is all different. This is why a fixed value such this rediculous 18ft rumor is impossible. It is not a fixed value. There are variables that must be accounted for.

In coax, Wavelength = (984 x VF) / Mhz.

Your coax between the split and the antenna has to be odd multiples of 1/4 wavelength. Since we're dealing with 1/4 wavelengths here, we'll use 246 instead of 984. The Mhz, for simplicities sake, is 27.4

It also has to be 75ohm coax, not normal 50ohm. 50ohm is what you use for single antennas on any two way radio or receiver. 75ohm is what is commonly used for CATV, not radio communication since it would be an impedence mismatch and induce loss. But since you're using two antennas, the two 75ohm cables balance it to the single 50ohm device.

Per the math:
RG59/U can be 5.9ft or 17.7ft. RG59/UF can be 7.1 or 21.3. RG6 can be 6.7ft or 20.2ft.
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Last edited by FireRanger; 04-12-2011 at 11:55 AM.
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  #27  
Old 04-12-2011, 06:51 PM
DangerRanger379 DangerRanger379 is offline
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Default Re: cb and antenna mounting.

sounds like he knows whats up....
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  #28  
Old 04-12-2011, 06:57 PM
richarddhoward richarddhoward is offline
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Default Re: cb and antenna mounting.

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Originally Posted by DangerRanger379 View Post
sounds like he knows whats up....
x2
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  #29  
Old 04-12-2011, 07:00 PM
DiabloBlanco DiabloBlanco is offline
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Default Re: cb and antenna mounting.

I think so. lol
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  #30  
Old 04-13-2011, 08:48 PM
Redbullbrett Redbullbrett is offline
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Default Re: cb and antenna mounting.

I like my Cobra 29 and my Francis antenna. It's clipped and has a swing kit. oh, and by the way, 2 antennas suck. Your taking your gain and splitting it in half to transmit. 1 antenna full gain. ME LIKEY.
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