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Author Topic: icom 706 static noise with more throttle???  (Read 878 times)

Posts: 572

« on: October 27, 2005, 08:15:57 PM »

heres the problem.i went from aa ts50 in the mobile.had it for 2 yrs with no static problems whatsoever.even with more throttle!now i went to a 706 icom,and it recieves excellent when idleing or with just ignition,problem is ,when im driving the highway and give my gm pickup more throttle,you can hear the static level{pulsation sound} gets about 2-3 s-units higher with more gas.noise blanker is on.if i let the gas off,it goes away.i never had this before with other radios,and know this is a common asked question.does anyone have any suggestions???i could live with it,but the ts50 was quieter.could it be grounding?? thanks.ve7ren

Posts: 657

« Reply #1 on: October 27, 2005, 09:09:57 PM »

It sounds to me as if you always had the noise, but did not notice it. I would be looking at grounds. The IC-706 has a Service Bulletin about board grounds, maybe that is a place to start.

Posts: 9930

« Reply #2 on: October 27, 2005, 11:00:47 PM »

I agree that good grounds are first place to start  run a ground from the radio to the floor near by, I use braid and a self tapping sheet metal screws right into the floorboards. I also ground the neg side of the battery to the wheel well, and the antenna (ground side) to what ever is close by.

next it sounds like an electric fuel pump. get in the vehicle and turn on the radio, then turn the key on but not to start.  if you hear a clicking noise, it is probably the electric fuel pump, "charging the system" and it should slow down, if no noise there, then start the motor and if the nois comes up now and increases with motor speed then its probably ignition noise.

in both cases, good grounds help, and some ferrite beads on the wires ( usualy several) may help.

point of intrest, if you use 1 ferrite bead, lets say it gives  a impeadence change of 10, if you ad a second bead it goes to 20 ( adds to the first, ) but if you wrap the wire through the bead  a second time it goes to 100 ( squares the impeadence) , and 3 loops will square it again.

so if there is room, try to get a couple of loops around the freeite bead..

hope this helps

tom N6AJR

Posts: 572

« Reply #3 on: October 28, 2005, 04:26:11 AM »

ok,but truck runs on fuel pump.i have it wired direct to the battery. i will try the grounding of the radio to the chassisand see if this works.the antenna is a hustler,that is grounded properly to the body.thanks.

Posts: 10248


« Reply #4 on: October 28, 2005, 05:41:39 AM »

One thing you have to be careful about is multiple grounds. For example, grounding the radio and any ancillary equipment to different places on the chassis of the vehicle. Doing so can create a ground loop, and ground loops are the hardest malady to find and correct. However, there is more to it than that.

I agree with the comment on the TS50 vs. the Icom. You weren't hearing the RFI from the ignition system previously. Depending on the type of ignition system you have (COP, wired, CPI), there are different noise abatement strategies.

I cover these and more on my web site, including examples of the more common "noises" we all have to address when operating mobile.

Alan, KØBG


Posts: 3288

« Reply #5 on: October 28, 2005, 07:26:14 AM »

I have a GM car, Buick, with Mk706 and just went through the car electrically bonding the hood, trunk and doors to the body.  I also put a strap on the exhaust pipe rear end to the chassis. It helped tremendously with noise and improved reception incredibly!!!!!!   Before I had an S3+ noise level and it dropped to 0.

What you are hearing is ignition noise. You can double check this, by going at slow speed, with no noise, then tromp the gas and accelerate.  A counter check against the fuel pump: When power is first applied by turning the ignition key, it runs for about 2 seconds to pressurize the lines.

Next I got toroid chokes from Radio Shack and started experimenting.  I use a remote head, and the most improvement was putting one on the control cable by the R/T with a couple turns.  That cable is shielded but needs to have the retaining screw installed at the R/T for good contact.  I've lost mine.

I put the little tubular RS computer type chokes on each ignition lead, and each ignition wire by the controller.  It helped a lot at low cruise (about 50mph) but higher and especially on accelleration noise is back.

For good measure I put chokes on the alternator output wire, the brake controller, and the two fuel injection controller valves on top of the engine.  They open and close at the same speed as the cylinders, thus are speed related.

The next thing I'm going to do is replace the spark plugs and all the ignition wires with the highest quality "resistance" type.  To the average joe, 100k miles is fine.  But they do break down with age and heat exposure.

Another way to check if your ignition wires are breaking down:  On a damp night, in the dark turn on the engine and look for a blue corona disharge on the wires.  Or on a rainy day does your noise increase?  Same thing.    This would explain why your noise has gotten worse over two years.

In my old RX-7 I used to replace the plugs yearly and the ignition wires every 25k miles.  Old technology, yes, but it made a difference with the noise.

Good luck OM

Posts: 3524

« Reply #6 on: October 28, 2005, 08:07:38 AM »

Try disconnecting the antenna and revving the engine.  If there's no noise in the radio with the antenna disconnected, it would follow that the noise is coming in via that route. The only way to eliminate this kind of noise is bypassing the various noise generating components to ground.

If the noise is still there with the antenna disconnected, then ferrites, chokes and such on the power leads might be beneficial.


Posts: 28

« Reply #7 on: October 29, 2005, 06:53:00 AM »

One explanation for the additional noise level when accellerating may be: When the piston is at TDC and the throttle is open, the actual PSI of the compressed gasses increases. This makes it take more voltage to ignite the spark across the gap in the spark plugs. More voltage at spark time = more noise.
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