Help with antenna setup and swr in a Jeep

[hacksaw]

Hello, I have posted this topic on another CB forum and had several answers but not really any explination. I have a 2003 Jeep Wrangler with a soft top. I am running a President HR 2510, a new TNT 350hd, and a 4' Firestik II antenna. I have a heavy duty aluminum L bracket half from a mirror mount, and bolted it dirrectly to the driver side rear of the Jeep tub above the tail light. I have taken a 1" x 10" copper ground strap and attached both ends to two bolts on the mount inside the body. I then buffed to bare metal, and ran two self tapping screws through the middle of the strap and into the body tub of the Jeep. I have also added the same type strap to the under side of the body and attached it to the frame. Also, yet another one of the copper straps from the body of the alternator and back to the fender well. The hood is strapped to the firewall also. I am about to run a piece of 4 guage wire from the negative post of my Optima red top and tie it to the frame also. There are two grounds comming off the batt and running to the engine, and to the firewall as well. Ok, now with that out of the way, on to power. I have ran 4 guage wire into a fused block, with 4 guage wire running to a terminal block mounted on the inside of the firewall. This is where the radio and amp get their power. Both power leads are about 3 ft to run to the 2510 and the amp. Both grounds for the radio and amp are running to a buffed part of the body and bolted down with self tapping screw. Very short grounds there. Now. With the amp out of line, and with a 3' jumper from the radio to an swr meter, and then a 18' coax from swr meter to antenna, the best I can get my swr is 1.6 on channel 19, and 1.8 on channel 1 and 40. This is the best I can get. When I hook the 18' coax to the amp, and then run a 6' jumper from the radio to the swr meter, and the 3' jumper from the meter to the amp, I get a swr reading of 1.2 on 19, 1.3 on 1 and 40. Why is this? It is my understanding that I should only run as much coax as it takes to get from the antenna to the equipment. I have no idea what I need to do, I believe I have confused myself! I also have noise from the fuel pump that will not go away. HELPPPPPPPPPPPPPPPP!!!

 

[hacksaw]

Oh yeah, also, what little testing I have done with the amp on, sometimes when I key the mic up, the winshield wipers turn on. And sometimes I can hear the wiper relay squeel when I speak into the mic. I have great reports from a station about 25 miles away from me, he said it has very clean audio and a very strong signal from a mobile to a base that distance. Anyway, I guess Ill wait for replys. Thanks and Merry Christmas

Shawn

 

[Robb]

Does it take 18 ft of coax to make it to the back of the amp to the antenna - in a Jeep?
Are you using RG-58 or RG-8 coax?
Does the radio w/o the linear amp on have the same problem with the windshield wiper?
How does the system behave w/o the meter in line?
Do you have a roll bar on the vehicle?
How come you didn't put the antenna on the top of the roll bar - if it has one?
Do you plan to use a filter between the radio and the battery?
Did you remove all of the fuses in the vehicles fuse box - and then put each one back in and test it with your radio - in order to find out which circuit is being most affected by the RF?

Some things to think about...

 

[hacksaw]

No Rob, it would probably only require about 10' of coax to make it from the antenna to the amp, and it does require 6' to make it from the amp to the radio. I would say that I could probably make it with a total of 14'. Coax is RG 58 UA, soldered PL 259's. NO, I have never had a problem with anything except for noise from the fuel pump, only when transmitting amp power makes the wipers come on. But not all the time. Yes, the Jeep has a roll bar, but, with the top on the Jeep, you could not do anything with it. I once had a link from here on building a rf filter using 12 guage wire 20' in length and wrapping it arround a bolt, or quick link for a large chain, and a cap. I dont know what the cap value was or where to solder everything. If I could find that link, I would make one tonight and install it to see if it helps with noise. I can remove the wiper fuse and the relay stops buzzing. It seems like its the only thing affected by amp rf.

 

[Robb]

http://www.worldwidedx.com/home-bre...-simple-alternator-whine-ignition-filter.html
Is this the link?

 

[W5LZ]

hacksaw,
About the only thing you have to worry about is that fuel pump noise (if that's what it is). The SWR, and change in SWR is pretty normal. What you are using for an antenna mounting bracket might have something to do with the sort of high SWR, antenna a bit too close to th rest of the vehicle, maybe? That's just a guess, don't take it as anything other than that! The SWR getting lower with the 'extra' feed line and amplifier in line is also fairly normal, and since it turned out 'better' than what it was to start with, it sounds like you're ahead with that change. Is that with the amplifier 'on' or 'off', BTW? If it's 'off', what does the change in feed line length and a change in SWR tell you? The simplest reason for that is that the antenna isn't tuned correctly, and would be my first thought (it's not 'R' = 50 and 'X' = 0), but not far off either. If it stays that way with the amplifier 'on', then that's good too.
That fuel pump noise filter isn't a bad idea at all. Depending on the particular fuel pump, it may take more than one, too. That wire wrapped on the 'link' needs to be of a size to carry the amount of current going to the fuel pump considering the 'extra' length being put in-line. The size of the 'link' is the limiting factor for the length of the wire used to make that choke. A little bit larger link and more wire certainly wouldn't hurt, just means more choking action. The capacitance of that capacitor can vary to some degree, larger not hurting anything. The only 'biggy' about it would be the voltage rating, and it needs to be at least 2 or 3 times whatever voltage it has to handle. A 'voltage surge' can arc one easily, so something like a 50 volt rating isn't bad (another 'bigger is better' thingy).

And completely beside the point, it looks like we're going to have a 'white' Christmas! Bah-Humbug! If I knew how to do it I'd stuff it all up 'Momma Nature's bloomers and see how she liked it! Had a light rain all day so also blessed with an inch or two of ice under it all... global warming my axe!
- 'Doc

 

[jessejamesdallas]

You can try the fuel pump grounding thing, and it may or may-not work...Worth a try I guess.

I never had much luck with filters, whether they were home made, or store bought tho...

At one time my Suburban was "eat-up" with fuel pump noise, and I tried RF Chokes, in-line noise filters, and never had much luck...Some of the noise would sorta fade out, but it was still there, just muffled up a bit.

Way I got rid of all the whining crap was to do some more grounding, and re-wiring of the set-up.

Like running all Power wires straight to the battery, running all ground wires straight to the frame (Radio, amp both grounded at the same bolt on the frame)

And believe it or not, my factory ground wire off the battery was NOT grounded to the frame, but to the fender...So, I also added another ground off the battery to the frame.

Then ground straps to all the doors, hood, tail pipes, and Transmission to the frame...(Personally, I think the ground strap off the tail pipes to the frame was the single biggest help of all!)

After all the ground straps were in place, "ALL" the whining noise went away! You can't tell anymore on the radio, if the motor is running or not...Zero feed-back from anything! Plus, it helped in tuning the antenna for a lower SWR. (this was a un-expected bonus)

One other thing you may want to try, is a different antenna...Since this is a Jeep, and going by where you have the antenna mounted, a 102" Whip would work perfect. Only draw back with the whip, is if you get a high SWR reading, about the only way to make the SWR meter read lower is to use longer jumpers of coax between the radio and amp and antenna...Usually, a 102" whip can be tuned between 1.3 and 1.8 fairly easily...Some say they can get a Whip to tune to 1.1 SWR (which I have yet to ever see) but average is between 1.3 and 1.5....

You can also add stuff like a spring or extension to make the whip longer (it needs to be 108" tall anyway) or you can also move the mount up higher toward the roof to improve your SWR reading using a whip antenna...(less reflect from the vehicle's body)

 

[rabbiporkchop]

jeep ground

There is a difference between a dc ground and rf ground. Use short lengths of braided ground straps for all your grounds. The shorter the better.

 

[highsider5]

i'm an electronic newb... mechanical is my field.. so fair warning there

on the jeep though, i have a jeep and the lack of a metal roof is the number one issue... mine came with a 4' firestick antenna on it when i bought it, and all i can tell you is that antenna is a POS... went down to radio shack, bought a 108" whip just like the one mentioned in this thread already, and suddenly my bone stock 4 watt all-in-one cobra worked great

i wrap with guys running a couple hundred watts, most with seperate amps, and most days i can talk to them just fine, over several miles which to me, is pretty good range given the circumstances which are.. legal radio, we commute around tall mountains, and i have the crappiest ground plane available

my whip is mounted at the rear center of the jeep, just in front of the tire carrier.. i ran a dedicated 6 GA braided ground out the back gate and up to the bottom of the antenna mounting lug, and like you i ground all the surfaces down to bare metal before bolting them up... using a basic meter i verified the ground was there, and using a cobra hand held, i can verify that i can talk to guys with way more radio than me

bottom line is toss the firestick in the hopper, its crap... i tried it vs the whip once, and that was the last time it was ever bolted up... i think it must be a noise filter in disguise as i couldnt even get static thru it most days

i have no clue what my SWR is in it, what length of coax i have, or anything technical other than i grounded the $%^& out of everything as that seems to be the problem in anything radio/amp/aftermarket whatever... its always a ground issue... anyways the whip, with lift, tops out at almost 14 feet tall and i'm sure that helps a ton.. the lack of metal ground plane, and the antenna not being centered are not pluses, but i get out under most weather conditions and i have no fuel pump noise

someday i'm gonna have a real radio, and a clue on what SWR i can achieve with it... until then, me and firestick's are seperated for life

good luck to anyone reading this old thread, maybe it will help since i know everyone who tries to run a CB in a jeep is pretty disappointed