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Balun for mobile

4

4600turbo

Active Member
Aug 27, 2006
151
0
26
Is it possible to use a balun for mobile application with a 1/4 wave antenna like the 10k predator?

Is the 10k predator on a mirror mount a unblanced antenna.

will using a balun help in keeping the Rf from leaking out of a coax and causing problems with gauges and sensors in my truck?
 

4600turbo said:
Is it possible to use a balun for mobile application with a 1/4 wave antenna like the 10k predator?

Is the 10k predator on a mirror mount a unblanced antenna.

will using a balun help in keeping the Rf from leaking out of a coax and causing problems with gauges and sensors in my truck?
Click to expand...

So the noise is radiated and coming from the coax?

The 10k is an unbalanced antenna and so is the coax, so a Balun (balanced-to-unbalanced) won't accomplish getting rid of the common mode currents. Try re-tuning and grounding the antenna, or as a last resort, use some ferrite beads on the coax at the antenna base.
 
I'd bet the gauges and sensors are simply responding to the fact that they are in the near field of an antenna. I doubt there's all that much RF "leaking" out of the coax. Some on-board electronics behave well in RF fields. Others don't.
 
Beetle said:
I'd bet the gauges and sensors are simply responding to the fact that they are in the near field of an antenna. I doubt there's all that much RF "leaking" out of the coax. Some on-board electronics behave well in RF fields. Others don't.
Click to expand...

Beetle you are probably right.

However, I would like to know what happened after the test procedures in the other thread I suggested were tried. having this data would make possible solutions so much easier...

:?
 
Oh, you are going to have fun! Had an older Nissan p/u who'z left turn signal and oil light just 'loved' RF. At higher power, the motor liked to slow down too. Most of it was my mounting method, not a very good ground at best (plate on bottom of antenna just fit in the center of the spare-tire, too lazy to drill a mounting hole). Ferrite and caps didn't do anything to help. They should in your case though. You need to be careful with the 'newer' computerized electrical systems, those 'cow-pastures' can do odd things when mixed with computers.
- 'Doc

PS - Cured my problem by getting rid of the 'filthy' amplifier and mounting the antenna correctly.

PPS - Those matching balun transformers usually get larger with the power levels. As in really huge, depending on the 'mix' used.
 
Haven't had time to attack the problem seriously yet, but as soon as I get home from this trip I'm going to get ferrite chokes. and try them out.

Is there a electical mesurement I should go by or just get one that fits the coax size?

I"ve made sure my ground was good and put in a filter on the alternator that about it so far.

I haven't tried to ground both radio and amp to the same ground yet. Will probably try that last.

Thanks for all the info I'm learning alot here on worldwide radio forum.

All you guys really seem to know your stuff.

NO on the Balun then.

The antenna is mounted about as good as it's going to get in a Semi-truck. It's on my mirror mount grounded to the metal door.
 
I guess I misunderstood what you were/are trying to do. The balun I was talking about was self-wound for matching purposes only, nothing to do with keeping RF out of the electrical system, sorry 'bout that.
Putting ferrite 'chokes' on the coax can help. Not that it definitely will, but it can, just have to try and see. What kind of ferrite choke? Whatever will fit, and you'll need more than just a few! A five gallon bucket of the @#$ things can come in very handy at times. Another solution (an ugly one) is to scavange the ferrite core of a TV's deflection coil. After you get rid of the miles of fine copper (<- CU) wire wound on the thing, be sure to save the clips that hold the two halves together. Clip the thing together and wind the coax through it as much as you can, and as close to the base of the antenna as possible (told you it was ugly, but it do work).
Good luck.
- 'Doc
 
ken white said:
4600turbo said:
Is it possible to use a balun for mobile application with a 1/4 wave antenna like the 10k predator?

Is the 10k predator on a mirror mount a unblanced antenna.

will using a balun help in keeping the Rf from leaking out of a coax and causing problems with gauges and sensors in my truck?
Click to expand...

So the noise is radiated and coming from the coax?

The 10k is an unbalanced antenna and so is the coax, so a Balun (balanced-to-unbalanced) won't accomplish getting rid of the common mode currents. Try re-tuning and grounding the antenna, or as a last resort, use some ferrite beads on the coax at the antenna base.
Click to expand...

Any antenna that works against a counterpoise is a balanced antenna. So, you are wrong in that the antenna isn't balanced. It works against the counterpoise that is the vehicle body.

The ferrite choke design your talking about is a balun, in the truest sense of the word. It was designed by W2DU, and is marketed as a W2DU balun.



But, you are right. It isn't going to help him. Better relief found in proper shielding of the trucks electronics in the first place, and in making sure the antenna leads don't go near any dc or sensor leads.




Hope this sets the record straight.


--Toll_Free
 
4600turbo said:
Haven't had time to attack the problem seriously yet, but as soon as I get home from this trip I'm going to get ferrite chokes. and try them out.

Is there a electical mesurement I should go by or just get one that fits the coax size?

I"ve made sure my ground was good and put in a filter on the alternator that about it so far.

I haven't tried to ground both radio and amp to the same ground yet. Will probably try that last.

Thanks for all the info I'm learning alot here on worldwide radio forum.

All you guys really seem to know your stuff.

NO on the Balun then.

The antenna is mounted about as good as it's going to get in a Semi-truck. It's on my mirror mount grounded to the metal door.
Click to expand...


Before you seriously throw money away, why not try star grounding all your radio crap, and then chasing the ground loops.

When you have a bad ground, it rectifies RF. Rectified RF is what is getting into your "gauges" and causing them to "do their thing", act like power meters / mod meters / etc.

--Toll_Free
 
Toll_Free said:
Any antenna that works against a counterpoise is a balanced antenna. So, you are wrong in that the antenna isn't balanced. It works against the counterpoise that is the vehicle body.

The ferrite choke design your talking about is a balun, in the truest sense of the word. It was designed by W2DU, and is marketed as a W2DU balun.

But, you are right. It isn't going to help him. Better relief found in proper shielding of the trucks electronics in the first place, and in making sure the antenna leads don't go near any dc or sensor leads.

Hope this sets the record straight.


--Toll_Free
Click to expand...

Toll_Free, you are wrong on both cases.

A balanced transmission system has the exact same signals traveling down the wires, 180 degrees out of phase with each other, in opposite directions. This is not the case with 50 ohm coax that is grounded at each end. If there is a different ground potential at each end, then there will be common mode currents which is non-ideal for a 1/4 wave monopole...

Maybe you should read the description on the coax and you will see it is listed as unbalanced.

Now for the Balun. A balun is a transformer used to match an unbalanced system to a balanced system. This requires a primary and secondary set of windings, which adding ferrite beads to the outside of a piece of coax is not. Ferrite beads are used to reduce common mode currents which should not occur in an unbalanced system.

If the system was balanced, ferrite beads would ruin the system...

So your comments do not make any sense when used togther. This should set the record straight...
 
Toll_Free said:
Before you seriously throw money away, why not try star grounding all your radio crap, and then chasing the ground loops.

When you have a bad ground, it rectifies RF. Rectified RF is what is getting into your "gauges" and causing them to "do their thing", act like power meters / mod meters / etc.

--Toll_Free
Click to expand...

As for ground loops, the signal to noise ratio deteriorates due to differences in potential at the various daisy chained gound connections which causes the noise to be magnified as it travels through all of the connections back to the source. This may also cause positive feedback/oscillations.

While a dirty connection may cause the ground signal to be nonlinear, it will make no difference when single point connections are used since everything is referenced to the same noise.

As for the suggestions on how to track down the problem, it has been suggested in one of the OP's other posts. That is why I asked what the test results were.

ken white said:
If you key up the entire system when the antenna is removed and it is connected to a dummy load, do you still have a problem?

If not, the antenna is causing the problem so try relocating the antenna and see if you can reduce the magnetic fields the sensor is coupling with.

If so, then the problem could be conducted or coax radiation.

Test the CB and amplifier with a short section of coax at the amplifiers output.

If the problem is still there, the problem is considered conducted, even though the power leads may be radiating electromagnetic fields and coupling into other circuits. Try running the power and ground leads, twisted togther using tie wraps to hold the twist, directly to the engine compartment. Connect the (+) lead directly to the battery's (+) terminal and connect the (-) lead to the engine block - this connection point will already have the alternator and battery (-) connected to it. The reason for the (-) lead connection at the engine block vice the battery's (-) terminal is because all of the engine sensors and alternator use this a the reference connection. Also, check and make sure the engines computer which is typically connected to the tub, has a good braid wire connection to the engine block as well. (1,405,200 miles!!!! Wow, the sensor could be bad...)

If the problem went away, the coax is radiating and additional grounding at the antenna with braid wire may help, or the coax will need to be re-routed so it doesn't couple into the sensor that is causing the problem.
Click to expand...
 
to tell if you have common mode currents on your mobile coax,,just move the coax around in your car while the swr meter is on an if the meter moves,you got common mode problem an your coax is tx,ing inside the car an your whole coax is acting as a antenna..
 
what are you using for coax to your 10k? i hope NOT rg59, or even 8x. some use the BEST coax at the base, but crap in the mobile. you'd be surprised how many mobile RFI (on rcv as well as xmit) problems can be resolved by using lmr400 or some other type of high % braided double shield coax. moving the antenna farther away from affected items helps as well. as was stated, also check/correct grounds, coax lengths, etc
 
Splash1 said:
to tell if you have common mode currents on your mobile coax,,just move the coax around in your car while the swr meter is on an if the meter moves,you got common mode problem an your coax is tx,ing inside the car an your whole coax is acting as a antenna..
Click to expand...

usualy you dont even have to move it around just grabbing the coax will usualy tell you if you have CMC.
 

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