How to improve my SWR with my current setup?

[TravisHauch]

I'm using a Cobra 75 WXST and a 2' Firestik II. I am using 12' of ASTATIC COAX. I used the factory antenna location but remove the factory wiring. I ground off the paint where it mounts so there is good contact. I modified a firestik stainless mount to hold the antenna. I also ground the screw holding the mount down to a bolt on a support.

Using a Radio Shack SWR meter. I get 2.5 on 1 and 3+ on 40. On 19 it ranges from 1.6 to 2. I've adjusted the screw underneath the cap and replaced the cap every time. I calibrated the meter every time.

It works I guess. I've gotten about 3 miles on the highway.

I would like to get a lower SWR but don't know what to do.

Any advice would be appreciated.


BTW, I'm going more for the stealth,stock look so if I can't get any better SWR the way it is, I can deal with it. The location is important to me.

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[drdx]

For starters, your biggest limiting factor here in terms of swr and range are the length of the antenna. If you just went with a longer antenna you'd see a world of difference. Many things influence the swr, and in your case it might be the location, coax, or the fact that it's a 2 foot antenna and that's the best you may ever see from it. A full size antenna is 9 feet, and you're asking a 2 ft. piece of fiberglass wrapped in a bunch of wire to do the same job, and it's doing the best it can, but it has it's limits. If that range is enough for you, then let it be. If you want to immediately double or more your range, get a longer antenna. Welcome, by the way and feel free to ask away, we're all casual here. -drdx

[dud muck]

I see some c0pper strap underneath the mount point in one of those pictures.
Is that what grounds the mount?
If so it should be braided.
Also the hood is the most important part of the ground plane for that antenna mounting location.
I would put a braided straps across both hinges.
Or at least strap between the hood and the antenna mounting point.

Hopefully your cb is getting its DC directly from the battery.

[TravisHauch]

I was thinking about going with a 3 ft. Silver Load instead. Wilson claims to have a few db gain on firestik. It would clear the height of my truck. Only thing is when I go into parking ramps, I'd have to be careful. I'm not sure what to do. Quick disconnect or a spring maybe?

[TravisHauch]

I see some c0pper strap underneath the mount point in one of those pictures.
Is that what grounds the mount?
If so it should be braided.
Also the hood is the most important part of the ground plane for that antenna mounting location.
I would put a braided straps across both hinges.
Or at least strap between the hood and the antenna mounting point.

Hopefully your cb is getting its DC directly from the battery.

I am using about 8" of 8ga. 735 strand wire for an added ground. There is a factory mount that held the am/fm antenna which I am also using as a ground. (The modified firestik mount sat on there nicely.)

I will ground the antenna directly to the hood and put a couple straps by the hinges.

The cb is not directly to the battery. I am pulling it off of accessory from the ignition column under the dash. I am a store manager at a car audio shop here and it was a good/easy location for me to obtain ample power. The ground for the cb could be better i suppose.

[TravisHauch]

I see some c0pper strap underneath the mount point in one of those pictures.

What you are seeing is the stainless piece from the Firestik mount.

[kg95]

The silverload is a great antenna.

I wouldn't hesitate getting any wilson except the little wil.

[TravisHauch]

Would you recommend me going with a 3' and possibly a spring?

[Foxhunter]

I see some c0pper strap underneath the mount point in one of those pictures.
Is that what grounds the mount?
If so it should be braided.
Also the hood is the most important part of the ground plane for that antenna mounting location.
I would put a braided straps across both hinges.
Or at least strap between the hood and the antenna mounting point.

Hopefully your cb is getting its DC directly from the battery.

I am using about 8" of 8ga. 735 strand wire for an added ground. There is a factory mount that held the am/fm antenna which I am also using as a ground. (The modified firestik mount sat on there nicely.)

I will ground the antenna directly to the hood and put a couple straps by the hinges.

The cb is not directly to the battery. I am pulling it off of accessory from the ignition column under the dash. I am a store manager at a car audio shop here and it was a good/easy location for me to obtain ample power. The ground for the cb could be better i suppose.

Sounds like you've made a good attempt so far. They are absolutely right about increasing the antenna length and that's wise of you to consider like you are. However you modified that stud, I take it it's still properly insulated with it's nylon bushing right? If you were using actual copper strap or flashing that's ok it's used in many marine and HAM applications---although a little stiff (why many prefer the braided strap). I would certainly, certainly, use direct supply lines from the battery both +/- and have them fused within 1 ft with an in-line fuse. That's easy enough to do and would be an easy upgrade. Stay out of/away from the vehicles ignition wiring and/or fuse block when possible. Any antenna RF ground wires if used should be kept short as possible. If they are long, (approaching length of 1/4 wavelength--9ft--) the ground wire can and in most cases will produce undesirable results becoming a very effective radiator. Hope you get it going.

[TX_Dj]

To put more simply what people are saying about your antenna length...

On my truck, I have a 102" whip. On your truck, you have a ~28" stick.

You will have to put about 14 watts into your stick to have the equivalent range that I have with 4 watts.

Similarly, if I drop 300 watts onto my whip, you'd have to put over 1000 (not recommended, you can't get your SWR low enough) into your whip to be equivalent.


Having said that, if your objective is to just talk a few miles down the highway, you'll do fine on any *clear* channel. On a channel like 19 (the one you probably are wanting to talk a few miles on the highway) you'll need better. Most drivers are running antennas longer than yours, and have louder radios. They'll squash you like a bug... but at least you should be able to hear them talking with each other, and should still be able to get useful information.

Also consider this... if your SWR is between 2.4:1 and 3.0:1, this means between 17% and 25% of the power you're putting into the wire is not getting out of the antenna. This means if your radio is "max legal power" and tuned like the manufacturer specifies, you're losing between 0.68 watts and 1 watt of carrier ("dead key") power, and between 2.72 watts and 4 watts of PEP ("swing") power.

Oh, and ground is king with any mobile radio. Your antenna is only "half the antenna". The other "half" is the metal of your car. Since most vehicles these days have various sections more or less isolated from the chassis and each other, it limits the ability of the antenna.

As others have also stated, braided strap is the more effective ground connector in an RF situation. The RF travels across the outer skin of the conductor, and 1" tinned copper braided strap offers far more surface area than 8 ga wire.

One more thing... I realize what you're saying about "stealth" in your choice of location... however, if your antenna does not have the majority of its length over the roof of the vehicle, you will get reflection from the vehicle, in your case most likely that pillar next to your mount. This will A) increase your SWRs even at low power, and B) will highly directionalize your transmissions to the front and right of the vehicle, which if my assumption is right that you're trying to get information from oncoming drivers on the highway, you're sending your power more "away" from that target audience.

Just my opinions, YMMV, etc... hope you get it sorted!