High SWR

[Fireball208]

I recently got a CB radio, but I haven’t figured out how to get the SWR down. The President Taylor radio I’m using has a built in SWR meter, & it says it’s absurdly high. However, when I hold my hand out the window & hold about 2/3 up the antenna, the SWR goes to 1.2. What’s happening?

 

[prcguy]

What kind of vehicle, what kind of antenna, where is the antenna mounted, yada, yada....

I recently got a CB radio, but I haven’t figured out how to get the SWR down. The President Taylor radio I’m using has a built in SWR meter, & it says it’s absurdly high. However, when I hold my hand out the window & hold about 2/3 up the antenna, the SWR goes to 1.2. What’s happening?

 

[Fireball208]

What kind of vehicle, what kind of antenna, where is the antenna mounted, yada, yada....

The truck is a second gen dodge. The antennas are dual firestiks, the trim to tune types. I have them mounted behind the cab, about 6 inches back in the bed. Before that they were on the mirrors, same problem. I moved them because I thought it was a ground plane issue but I’m assuming not since the same thing is happening with them behind the cab.

 

[prcguy]

Mounted on top of the bed rail? Using stake hole mounts? If stake hole is the coax grounded to the bed rail? Are you using a factory phasing phasing harness to split for two antennas?

The truck is a second gen dodge. The antennas are dual firestiks, the trim to tune types. I have them mounted behind the cab, about 6 inches back in the bed. Before that they were on the mirrors, same problem. I moved them because I thought it was a ground plane issue but I’m assuming not since the same thing is happening with them behind the cab.

 

[Fireball208]

Mounted on top of the bed rail? Using stake hole mounts? If stake hole is the coax grounded to the bed rail? Are you using a factory phasing phasing harness to split for two antennas?

Yea top of the bed rail, not stake hole mounts, not sure the right work for them. Basically a piece of angle iron. I’m using a splitter off amazing…. May not be of the highest quality.

 

[prcguy]

Describe the splitter. Is it a coax connector with two equal lengths of coax about 18ft long each or is it a box with three connectors?

Yea top of the bed rail, not stake hole mounts, not sure the right work for them. Basically a piece of angle iron. I’m using a splitter off amazing…. May not be of the highest quality.

 

[Fireball208]

Describe the splitter. Is it a coax connector with two equal lengths of coax about 18ft long each or is it a box with three connectors?

Like the T shape. I had an old one before that was two coax cords out of one connector, thought maybe it had a short in it.

 

[SmitHans]

The antennas are dual firestiks, the trim to tune types.

Have you actually tuned them?

 

[prcguy]

I don't understand what the T shape is but I would stick with the two coax's out of one connector type and leave it the factory length. Did you check the old one for shorts?

Like the T shape. I had an old one before that was two coax cords out of one connector, thought maybe it had a short in it.

 

[slowmover]

 

[atech]

Antenna coil can NOT be near metal or the truck cab! Move the coils above the cab! That`s mirror or truck mount. Adjust (both) antenna tips (the same amount).. If you have the correct phasing harness! This situation happens a lot on motor homes for example. Get the coils above the roof on a mirror mount and it will work!

 

[Fireball208]

Have you actually tuned them?

I’ve tried. SWR stays up in the 4+ range

 

[Fireball208]

Antenna coil can NOT be near metal or the truck cab! Move the coils above the cab! That`s mirror or truck mount. Adjust (both) antenna tips (the same amount).. If you have the correct phasing harness! This situation happens a lot on motor homes for example. Get the coils above the roof on a mirror mount and it will work!

The antennas are long enough that they stick a good 1.5 feet above the cab of the truck

 

[n5ims]

You might try a single piece of 50 ohm coax going to one of the antennas alone. That's the simplest you can do and if you get that to work correctly, move to the other antenna and try that. If both are good with low SWR, THEN try the cophased dual antenna setup. Just remember that with cophased dual antennas, the coax length and type connecting them is VERY important. Most often this coax is 75 ohm and 18 feet long each and they MUST be the EXACT same length. The coax from the splitter to the radio should be 50 ohm and can be of any length (the shorter the better).

Just remember that a cophased antenna is directional and when mounted like most truckers do, it will work good to the front and rear of the truck but poorly to the side of the truck. Truckers use them for two reasons, 1) their mirrors are very close to the correct distance the antennas need to be apart to work right, and 2) they mainly want to talk to folks in front or behind them and don't really care about those to the side. Smaller vehicles may not have the width to properly mount the antennas so they work as intended.

 

[slowmover]

I go to a lot of trouble on the big trucks I’m assigned to get a dual antenna system to work well.

But I wouldn’t have a set on my pickup as it’s not the right way to get best performance. (Roof center is my choice).

There’s a learning curve, but it isn’t terrible. It’s real satisfaction to hear and get heard. A CB is a tremendous tool for the road.

Tech-Docs Index

https://www.wearecb.com/cb-radio-blog.html

There are more layers yet (wanting better performance), so stick to it!




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[slowmover]

https://simonthewizard.com/2019/11/19/new-usa-cb-president-taylor-fcc/

President Taylor CB Radio

TAYLOR FCC (12/24V) - AM-transceivers - CB-Radios - Group President Electronics USA

Auto-SWR means no separate meter needed. (See Menu)

Smaller than a Cobra 25. That’s a nice size.

As a brand it’s hard to go wrong with PRESIDENT. I’m pleased with the gear from them that I have.

My pickup is getting a Lincoln 2+ and a Texas antenna.

.

 

[prcguy]

If this is what the OP is using for splitting to two antennas he must use equal and critical lengths of 75 ohm coax to each antenna. If you use 50 ohm coax it will never achieve a good match. The suggestion of connecting just one antenna using 50 ohm coax for a test is a good idea.

View attachment 129292

 

[SmitHans]

The truck is a second gen dodge. The antennas are dual firestiks, the trim to tune types. I have them mounted behind the cab, about 6 inches back in the bed. Before that they were on the mirrors, same problem. I moved them because I thought it was a ground plane issue but I’m assuming not since the same thing is happening with them behind the cab.

My guess is it is the t-splitter causing the problem. You really need to have a proper cophase harness.


ALSO:

If those antennas require a ground plane, neither the mirrors or the bed rail will give you a good ground. You would be far better off with a single antenna in the center of the cab roof. If you insist on mirror or bed mount, you need antennas that do not require a ground plane.

Make sure you have the correct coax - 75 ohm for duals. 50 ohm for single.

Also make sure the studs are not touching the mount - are you using the nylon washers that are supposed to be there?

If less than half of the antenna is above the roof of the cab, or if it has a coil that is below the cab roof, it will negatively affect SWR.

Check all your coax for continuity - any worn or crushed sections of coax can cause high SWR.

Keep in mind that even if you do get the SWR down, pickup trucks aren't wide enough for effective cophasing of CB antennas. Your dual setup will give you range directly to the sides of the vehicle, & almost nothing front or rear. Correctly cophased antennas on a semi truck enhances front & rear range at the expense of range to the sides.