Help with RF interference from a rectifier

So I installed my home patrol scanner in the car , since it's a smart scanner I doesn't work unless I use a voltage reducer to bring the 12v dc down to 9v dc for power, now that there's a rectifier I'm getting static interference on the scanner and my ham radio...

What's the easiest way for me to get rid of the interference?

Thanks in advance

Do you mean a voltage reducer instead of

rectifier? A rectifier is used to help change AC to DC voltage. For reducer you would use something in the order of a regulator. I thought that the home patrol was 12 volt. Saw where it is 9 dc.

Yes that's what I meant lol and the home patrol unfortunately only accepts 9v DC in , when u apply 12v DC a message displays " illegal voltage " on the screen

miserytom said:

So I installed my home patrol scanner in the car , since it's a smart scanner I doesn't work unless I use a rectifier to bring the 12v down to 9v for power, now that there's a rectifier I'm getting static interference on the scanner and my ham radio...

What's the easiest way for me to get rid of the interference?

Thanks in advance

Click to expand...

I believe what your trying to describe is an inverter power supply built into the plug that goes into the DC connector on the dash of a vehicle. The oscillator circuit in the plug is what is generating the noise. Most companies that make these cheap inverters, don't care about any radiated noise they may make. Very few times does a consumer call them on the carpet for the generated RF noise they may make.

One solution is to get some 500 MA or 1 amp. diodes and put 7 of them in series. This will drop the voltage from the 13.5 nominal volts in a vehicle to the 9 volts you are looking for. Each diode should cause a 0.6 volt drop.

Wire them with the cathode to anode and solder the connections. Put the cathode to the scanner and the anode end toward the vehicle source. Leave some wire between the diodes so they can be folded back on each other. Find some soft shrink tubing and slip is over all the diodes. Take the shrink tubing and cover the diodes, but don't pit the heat to it yet. Fold over 3 of them at a time. Then once they are folded back and forth, heat the shrink tubing just enough to get it to start to shrink. Then use another length of a larger size and sleeve the whole thing, including the wiring between the vehicle plug and the scanner cable connections.



Your noise should be gone and the scanner happy with the voltage it is getting.

It's actually an inline reducer, I don't deal with lighter plugs lol everything I do is hardwired

Would a ferrite bead/choke help ?

Use an LM7809

I used an LM7809 9 volt voltage regulator in my vehicle with no other components. I mounted it to the steel frame under the dash for heat sink and hard wired it to my switched 12 volt radio system in the vehicle. With heat sinking it is good to 1.5 amps. This is a linear device so there is less chance for noise, it powers my Radio Shack Pro-106 without issue.

Best part they are very inexpensive, for example:

http://www.amazon.com/L7809CV-Termi...ie=UTF8&qid=1446993188&sr=8-1&keywords=lm7809

You will need to spend the money to get a quality DC-to-DC stepdown. Switching power supplies are inherently noisy (there are lots of resources online if you are interested in why).
You can also spend the money and much more time cleaning up the one you have by putting caps and chokes and encasing the unit it's self in a RF cage. It will not be a simple fix we can give you in a single post.

Good luck.

Bruce

12v to 9v

Radio Shack sells a 12v voltage reducer. If the noise comes from your car motor, replace the spark plug wires with resistor wires.If it comes from the alternator .,use a filter or connect to battery.

I'm pretty sure the noise is coming from the reducer as it's a static noise , none of the old wine type noise

Tom,

As others have stated I'd check the quality of the step down device you are using first. Even if it's a quality device it could be defective or simply not a good match for your vehicle. Also check your connections and path you followed for wiring. If you ran in parallel with other wiring for some distance you could pick up noise there. Also make sure you have a really good ground connection that is as short as possible (not the battery). Make sure all the paint is scraped away from where ever you bolted that ground wire so you have a solid connection. Make sure you are using wiring that is heavy enough gauge for that task - a bit heavier is better than too small a gauge.

I see you are a ham. Not sure if you are an ARRL member. Regardless the ARRL has published the "bible" on rfi for quite some time. It's highly respected as an authoritative source for rfi of all types. I'd suggest checking it out.

ARRL :: Technical :: The ARRL RFI Book 3rd Edition

12v to 9volt

Because your car is 12volt dc ,you do not need a rectifier . A rectifier is only used AC TO DC. you need a resistor to cut down dc volts.

wb6uqa said:

Because your car is 12volt dc ,you do not need a rectifier . A rectifier is only used AC TO DC. you need a resistor to cut down dc volts.

Click to expand...

Who is saying anything about a rectifier? The problem is noise. Trying to drop the voltage with a resistor is heat and the voltage out from the resistor will change with current draw.

You can use an IC voltage regulator as one person suggested. But again, it will generate heat. You will need a heat sink using an IC regulator. It would also be a good idea to include a filter cap or 2. One to smooth the ripple and one to clear up any spikes.

My suggestion of using the series string of diodes is the simplest. You get a 0.6 volt drop from a silicon diode. So just make up a string to drop to the voltage you want. If you use a decent sized diode, like a one amp type, there will be little to no heat to worry about.

Who??? The tile of the post is Help with RF interference from a rectifier

jim202 said:

Who is saying anything about a rectifier? The problem is noise. Trying to drop the voltage with a resistor is heat and the voltage out from the resistor will change with current draw.

You can use an IC voltage regulator as one person suggested. But again, it will generate heat. You will need a heat sink using an IC regulator. It would also be a good idea to include a filter cap or 2. One to smooth the ripple and one to clear up any spikes.

My suggestion of using the series string of diodes is the simplest. You get a 0.6 volt drop from a silicon diode. So just make up a string to drop to the voltage you want. If you use a decent sized diode, like a one amp type, there will be little to no heat to worry about.

Click to expand...

noise

a car has a computer that can put out a lot of noise.

Well I think it's fixed , I noticed on the original power cord for the scanner there is a ferrite bead, so I put that inline after the resistor/reducer I have and it seems to have done the trick

Thanks for all the input guys