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692
Junior Member
Username: 692
Post Number: 20
Registered: 7-2002
| | Posted on Sunday, April 11, 2004 - 1:48 pm: | 
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Would there be any difference between the two.
Say i run a 18-foot co-phase harness. or 2 pieces of 18-foot coax. I have 2 SW-2000 Wilsons, With ground wires run to the frame,with 9-foot coax per side. With one Antenna hooked up SWR is perfect.But with both hooked up SWR is 2.5. So i thought i would try the 18-foot setup and se if anything changes, Another problem is it picks up the factory installed Refrigerator, you have to turn it off to talk any distance. Disconnect coax and noise is gone. (PS 2004 KW T-600).
Thanks 692. |
Kc0gxz
Advanced Member
Username: Kc0gxz
Post Number: 733
Registered: 3-2003
| | Posted on Tuesday, April 13, 2004 - 4:56 am: |
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692
CB antenna systems are designed around a 50 ohm feed point impedance, and so is the most common types of coax. This is all fine until you try to operate two antennas together. Running them together like this in an electrical "parallel" relationship will give you a total impedance of 25 ohms. That's why your SWR meter is seeing a 2:3 or more mismatch. And it's death to your finals if keyed up too long.
In order to run co-phased antennas, you "HAVE" to run two strings of 74-76 Ohm RG-59U coax cut in exactly 18 foot lengths. Doing this with at least a 1/4 wavelength spacing (9ft) between the antennas will result in a fairly good match. However, 18ft spacing would be even better and it would have a much wider radiation pattern.
Just remember, a truly co-phased harness has an impedence of around 74 to 76 Ohms. Co-phased harnesses are usually sold as a "75 Ohm Co-Phased Harness". Just go to your local truckstop and pick one up. They're cheap.
I've never seen the point in running co-phased antennas on pickup trucks because you never get the antenna spacing needed in order to get them to really work correctly. They work well on the big trucks because they eliminate any dead spots caused by the long trailor. Also, when set up like that, the antennas talk best to the front and rear because there is practicaly zero "ground plain" (no metal) for the antennas to talk off of the sides of the truck. In otherwords, an antenna will talk best in the direction that has the most metal.
I hope this has been of some help to you.
Jeff, kc0gxz. |
692
Junior Member
Username: 692
Post Number: 21
Registered: 7-2002
| | Posted on Wednesday, April 14, 2004 - 2:27 pm: |
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Thanks for the response Jeff. I am going to run new 18-foot co-phase as soon as i can. I also have a Boomer 400HD that i would like to put in, How long should my jumper be. I would probably need at least 3' from where i would have to mount it. I am looking real hard at the new Magnum S-3. Sounds like a real Powerhouse. I was just waiting for some more reviews and reports.
I will check back tomorrow.
Thanks. 692 |
Kc0gxz
Advanced Member
Username: Kc0gxz
Post Number: 740
Registered: 3-2003
| | Posted on Wednesday, April 14, 2004 - 11:58 pm: |
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692
LOL, personally, I only use a 3ft patch cord. Since I didn't have any SWR problems with that, I left it alone.
According to the advertized specs that Copper shows, their Boomer has "4" 1446s in it. Just keep in mind that the death of most solid state amplifiers is caused by heat. And these babys do generate some heat. You might want to consider one of Coppers fan kits for this amp. It wont give you more horsepower but it sure will let the amp run cooler.
Jeff, kc0gxz. |
692
Junior Member
Username: 692
Post Number: 22
Registered: 7-2002
| | Posted on Thursday, April 15, 2004 - 6:06 pm: |
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Thanks for the info, I knew from what i have read on the Magnum that you should have a 4 pill Amp, Just didnt know which pills mine had in it. I will probably put the Amp plans on hold till i get my SWR problems sorted out. This has been the worst Truck i have ever tried to set up. Everything that has worked good in the past (Same makes and model) is not working now. Thanks again for the information. I know most of the basics to everything,Just not the technical stuff. And from seeing your Call Letters i am sure you do.
ON THE ROAD AGAIN!
Be back tomorrow night. 692. |
692
Junior Member
Username: 692
Post Number: 24
Registered: 7-2002
| | Posted on Saturday, April 24, 2004 - 11:28 pm: |
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Just thought i would let you know i tracked my problem down to a bad antenna stud. I put both of them on new when i got the truck new last year. Also i trashed the 9-foot coax, went with 18-foot and the SWR is perfect(after retuning). I got better SWR readings with the 6-foot Wilsons than the 2000 Wilsons. These trucks use the low profile mirrors so i figure the taller top loaded antennas will probably work better anyway. Now if i can get that annoying static that the radio is picking up off the refridgerator when it is on. Had the auto parts to order a capacitor to put in the hot wire that goes to the fridge. Quess i will make that next weekends project.
692. |
