High SWR after Amp.

[Ike]

I'm sorry for asking so many questions but I'm really stumped with this.

I will admit that I'm not using a good SWR meter, it is a cheap astastic but with it I was able to set up a radio and antenna in a friends truck. We went from 1:3.5 and not being able to transmit further than across town (small town) to 1.1.5 with it and I can hear him about 7 miles away on the interstate and 20 miles over water.

Using the same meter I was able to get my mobile antenna, a wilson flex 3', down to 1:2 I had to take the tuning rod all the way out. with this we were able to talk that 20 miles over water, it was static filled though after about 15 miles.

I added the amp and my SWR is now almost at 1:4. I bought a 4' wilson flex and a no-name truck stop 4' flex antenna. I can't seem to get either one of them lower than this SWR. I am going to try a Firestik Firefly to try as well. I have replaced my jumper from cheap radio shack coax to mini8, its the best I can find around here. And will be doing the same with the run from the amp to antenna.

It is in a FJ Cruiser using a Bandi Mount. I want the flex antenna as it bounces around off road and seems to hold up the best.

I can not be heard any further than I could before the amp and my signal isn't as strong sounding unless I'm right on top of the other station. My receiving is full of static too.

Do you guys think changing the coax from the amp to the antenna could make a difference to bring my SWR back where it was? If not I think I'm going to dump the amp. I was happy with it before it, just hoping to talk a little further out.

Thanks for any help

 

[Robb]

Most SWR meters - including cheap Radio Shack units - will do SWR just fine. Don't blame the meter. If your SWR is 4 to 1 - don't talk on the radio/amp. Stop. You will FRY the amp/radio.

It is cheaper to replace the patch cable between your amp and radio, and coax on your system - than it is to fix your radio and amp.

The transmitting distances that you are talking and comparing isn't valid. Conditions change all of the time, as much as the terrain you are travelling on. Or whatever direction you are pointed - these all will affect your perception of how well it is transmitting. What matters is that you correct the problems before you start wasting parts/equipment.

 

[Ike]

Thanks. Ill try to get all the coax changed tomorrow. I have a new mini8 jumper between the radio and amp. Have to undo my sealed up hole to get the new coax to the antenna.

I hooked the antenna back up directly to the radio and the swr went back to 1:2.

My swr with the amp in line, with it off, is pretty close to 1:4.

Im checking it with the amp off, what is it about the amp just being inline that will raise it so much?

 

[Robb]

Is it 1.4 to 1 OR 4 to 1?
Biiiig difference!

If the SWR is WAAAAY off; then the antenna has a problem or the coax or connector is fautly. Or the solder job.

 

[Ike]

I may be explaining it wrong. Im checking on channel 20 for the time being. I key up with the switch on FWD and turn the knob to the SET line then switch to REF. without the amp in line the needle drops to 2. I was told that this is a 1:2 with the amp inline, but off, the needle drops to right under 4, in the red.


Im thinking it may be a problem inside the amp causing this.

 

[W5LZ]

Ike,
From how you describe what's happening, the amplifier seems to be at least part of the problem. Another part of the problem is that your antenna doesn't appear to be tuned as well as it could be. And although RG-8x coax doesn't have the best reputation in the world, I very much doubt it it's any part of the problem at all. Another part of the problem is that you are 'new' to all this and may not understand what the whole process of tuning an antenna system is all about.
The easy part first! None of us knew what all this stuff was about when we first started so it's certainly not something to be particularly worried about. (Except me, of course, I was talking to the doctor that delivered me about antennas when I was born. He got embarrassed about being so 'dumb' and actually spanked me and made me cry! Can you believe that?) So, a little clarification to start with.
To work well, an antenna has to be 'tuned'. That means that it has to be adjusted so that the radio 'likes' what it sees. Which means that it has to have a 50 ohm input impedance which will be the same as the feed line's (coax) impedance, 50 ohms, and the radio's output impedance of 50 ohms. When all of those are 'perfectly' matched, the SWR is then 1:1, or one to one. Like anything else that's man made, you are almost never going to get things perfectly matched. But that SWR (Standing Wave Ratio) is a measurement of -how- close things are matched, and that means that getting it as low as possible is good. The higher it gets, the less the radio likes it and if the radio doesn't like it much, it just isn't going to put out as much, so the worse the resulting signal. All kinds of analogies for that, pick the one you like best. Feeding your cars engine the wrong 'size' or amount of fuel and it not 'putting out' as much performance is a good one. That SWR reading can tell you how 'close' you are.
That's not an exact explanation by any means but it'll get you into the ball park of antenna tuning. Now for some numbers. An SWR of 1.0:1 is the ideal. Anything from about 1.5:1 (one point five to one) and lower is actually good enough. From about 2:1 (two to one) and up is not so good to very bad. Your described SWR being about 2:1 to 3.5:1, means your antenna isn't tuned well and especially when using an amplifier, falls into the very bad category. That's because a high SWR and high power typically means something is going be damaged. I would suggest NOT using the amplifier until you can make things better.
Now for some of the "but's" you'll always find in things dealing with SWR and antenna systems. Any and everything that's 'in-line', connected to the feed line/coax, will affect what the SWR will end up being, or can change it. Your SWR going from about a 2 something to a 4:1 something when you put the amplifier in line means that there is something 'not right' about that amplifier. No one can tell you exactly what that 'not right' thingy is without some additional checking (you can get a few good guesses about it, but that's all they are, guesses). You have two choices. Learn more than you ever wanted to know about electronics and fix it your self. Or, take it to someone who knows what they are doing and let them fix it. One takes time, the other takes money. Your choice (I'll bet I can tell you what most people in your circumstances do, and I'll bet you can too).
And now for the disclaimers.
I am not a good teacher. I do not know all there is to know about this stuff. What I do know I learned through experience, which is just another way of saying I have made the same mistakes as everyone else does (at least once), and is a terrible way to learn anything! All of this a generalization, which means it is never always completely correct in every circumstance. Your millage may vary. No one in their right mind would pay me to do this $#;+! Which is about the only 'absolute' in this whole mess.

Best advice I can give you is to find someone who knows what they are doing and have them look at ALL of your set up, not just one particular part of it. Which is a pretty good 'trick' all by it's self... sorry 'bout that.
Good luck!
- 'Doc


(and just to clarify a little, that "Doc" is just a nickname. The only thing I've got a 'doctorate' in is cheapness!)
... and you hear me humming... "Oh Lord, it's hard to be humble, when I'm perfect in every way"... as I walk off into the sunset...
...all puns intended.

 

[C2]

Make sure you recalibrate the SWR meter after you switch on the amp.

What amp are you using?

Is your amp and antenna grounded and do you have adequate ground plane?

Where is the antenna mounted?

Here are some possibilities:

common mode currents radiating back down the coax. You might find it difficult if the antenna is on the side of the vehicular. You may also have high RF field inside that is being picked up by the meter. Better grounding will help this here. Make sure antenna mount is well grounded. Make sure the amp has good power supply and that it is well grounded. Ground the radio chassis too. You might also ground the doors, hood, body to the frame with braid.

High harmonics. Is the amp being overdriven (which amp and what is the output power level and drive level on dead key)?

SWR meters can be more responsive at higher powers, meaning at lower powers, they may indicate a better SWR that what is really present.

This all assumes that you have good coax.

 

[dudmuck]

FJ Cruiser using a Bandi Mount.

Google around for that. You'll find there is an FJ cruiser web forum, where they're using that same antenna mount.
Cobra 75 WXST and Bandi Mount Install - Toyota FJ Cruiser Forum
"The biggest issue most people are going to have with this install is grounding. Make sure the Firering is grounded to the Bandi mount. Might have to really tighten things down.
To make sure you have a good ground, you have to scrape some paint on the mount and on the hinge (all covered in Bandi's instructions)."

No one in their right mind would pay me to do this $#;+!

who is going to pay me for my time reading that long dissertation?

 

[hotrod]

i didnt see it mentioned but what type of mount ya using and where do
you have the antenna mounted?location of antenna may/can play a role
of how accurate your swrs will be

 

[W5LZ]

dudmuck,
You get half of whatever I get for writing it.
- 'doc

 

[SR385]

Just to double check...the SWR meter is between the amp and antenna right?

Also, I would strongly recommend with an amp not to use those skinny flex antennas, particularly if the amp does a few hundred out.

For banging around, a stainless whip is nearly indestructable. Go with a short shaft Wilson trucker or something like that with more metal in the air, the performance will be better.

How sure are you that your mount has bitten cleanly down to metal through the paint? That's another very common issue...not a solid enough ground connection.

 

[BOOTY MONSTER]

i can definately see that mount dammaging coax if it isnt installed correctly .
New CB Antena Mount !!! - Toyota FJ Cruiser Forum
id also think that if your anatnna is mounted similarlly to the one in the pic seeing how it is only 3 foot tall that having most of it below the truck will cause issues/reflect and adding power will increase the effects . check your mount to be sure it isnt pinching your coax or putting too tight of a turn radius on .

wilson has been having problems with their fiberglass antenas lately also . if the mount and coax are good id put a different antenna on it a 5 ft or taller sharp shooter if you wanna stick with fiberglass . IF.......i were mounting on the side of my vehicle id want at least 2/3 of the antenna above the vehicle . if you go with a wilson or k40 trucker series dont use the short shaft one . get one with a shaft long enough to have the coil on the antenna above your roof when its installed .

what size amp are you running ?

also welcome to the forum and dont worry about asking questions . we all come here to learn and maybe share a lil .

 

[SR385]

Ohh it's sort of mid-height mounted. yeah put a long shaft Wilson Trucker on that one just like he said, so the coil is just above the roof line. The whip will put up with all the abuse you can give it. If you want a bit of safety, stick a stiff spring under it at the mount...you'll have to tune the whip with the added length of the spring of course.

 

[Ike]

I am using the Bandi Mount but not the Firering, I have a traditional stud on it. The mount is grounded using a strap and not just the little nut they give you.

I have put the new Wilson 4' flex antenna on. Without the amp the swr is 1.7. It was 1.5 until I put the rubber cap on.

With the amp the swr is about 3.5, this is with the amp off but inline with meter between amp and antenna. The amp is a Palomar 80. Are these known to have problems that could throw things off like this?

I took the amp out of the truck for now until I can devote enough time to make it work right. I just can't right now. I have noticed improved reception with the taller antenna, and I was able to transmit to an area today that I usually lose people before they get to.

I am happy with the set up now, just wish I could have extra power of the amp.

Thanks for all the help and suggestions. In a few weeks I hope to be able to get back to this.

I will take a look at those wilson trucker antennas.

 

[mackmobile43]

I believe you're pissing in the wind trying to run an amp through that antenna, if the roof of that rig is not metal that only makes things worse because the antenna sees no counterpoise so your reflected power from this issue will give you a high swr reading.