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Lt Dan · #1 10-21-2009, 08:11 AM

Hi, I have some engine noise whenever I turn on my engine (obviously), it changes speed with the engine speed and when the engine is off it goes away.

I know I need a noise filter but I don't know where to start.

What brand?
how big?
etc...

Keeping in mind I'm running a Northstar 450 BFM with mosfet finals, so I need alot of power vs a regular radio.

Thanks guys

sp5it · #2 10-21-2009, 08:30 AM

Disconnect the antena to check which way noise is coming. If noise will disappear it means, that it is coming through antenna, so you need to locate part of your car which is generating the noise, than put the filter on it.
If noise is coming to the radio through power cables put filter on the cable as cloce to the radio as you can. I put into my radio

Mike

Lt Dan · #3 10-21-2009, 08:03 PM

Quote:

Originally Posted by sp5it

Disconnect the antena to check which way noise is coming. If noise will disappear it means, that it is coming through antenna, so you need to locate part of your car which is generating the noise, than put the filter on it.
If noise is coming to the radio through power cables put filter on the cable as cloce to the radio as you can. I put into my radio

Mike

i think its coming from my alternator...

yeah when i uplug the coax is DOES NOT go away

W5LZ · #4 10-21-2009, 08:33 PM

You may not believe it, but that's noise not going away with the antenna is better than if it did. Filtering the power line is much simpler than the antenna type noise.
All nise is either AC or a 'pulsing' thingy, and botha re handled the same way. Basically, don't let any AC get to the radio. A very handy thing about capacitors is that the let AC get through them and no DC. So use a capacitor to 're-direct' any AC to ground instead of going through that radio. A capacitor from the 'hot' (+) wire to ground (-), does that very nicely and still doesn't provide a direct short for DC. To a completely ridiculous point, a bigger capacitor is better than a little capacitor when doing this. It can get a little 'sticky' if you let it, because how much AC/noise a capacitor will let get through is related to the frequency of that noise. There are formulas for that if you just have to know, otherwise, just use a higher value capacitor and don't worry about it. A sort of 'average' capacitance value for noise is something around 0.1 uF. If you wanna use a 1 farad capacitor, be my guest, but they get sort of expensive and dangerous. The other way capacitors are rated is by how much voltage they can handle. That's a real "iffy" thing if the voltage is not constant. If the voltage can surge, you want a cap that can handle that amount of surging voltage. So a minimum of 2 or 3 times the applied voltage is barely adequate, sort of. For 12 volt systems, a voltage rating of 50 volts is NOT too much by any means (especially for those 1 farad caps, even 100 volts wouldn't be too much). So look for capacitors that are at least 0.1 uF, @ 50 V. It may take more than one, or 2, just depends on the noise. Ceramic disk capacitors are very common in that size, and are cheap. There are polarized capacitors that can be much larger and cost a bit more, but they HAVE to be connected correctly or they certainly will pop no matter what the voltage ratings are. Stick with the ceramic caps, they can go either way (kinky, huh?).
Most cheaper line filters are just a bunch of capacitors in some kind of container. They work.
There's anothe electrical doo-hicky that can help. It's called a 'choke', and it lets DC through if and stops AC. A choke is just a sort of large coil. It has to handle all the current that whatever it's connected to will draw. That means that the wire used to make that coil is larger than you might think. The secondary windings of a 12 volt transformer are an example of that 'largeness'. The wire used is typically 10 to 100 times as large as the wire in the primary side of a transformer. that's one source for a choke if you happen to have a few dozen old transformers laying around. If not, then you can make them fairly easily, there's even a thingy about that on here somewhere.
A choke goes -in- the 'hot' (+) wire, NOT to ground. If you combine a capacitor and a choke you get what's called an 'LC' filter, and you will find them on just about every power supply that's filtered, all of them. So in effect, you are just adding a common power supply filter to your radio.
There ya' go, more than you ever wanted to know about filters. But it do come in handy, especially if you're as cheap as I am...
- 'Doc

Beetle · #5 10-21-2009, 11:40 PM

For alternator noise, a lot of folks have had good luck with these:

New Page 1

Lt Dan · #6 10-22-2009, 05:44 AM

Quote:

Originally Posted by W5LZ

You may not believe it, but that's noise not going away with the antenna is better than if it did. Filtering the power line is much simpler than the antenna type noise.
All nise is either AC or a 'pulsing' thingy, and botha re handled the same way. Basically, don't let any AC get to the radio. A very handy thing about capacitors is that the let AC get through them and no DC. So use a capacitor to 're-direct' any AC to ground instead of going through that radio. A capacitor from the 'hot' (+) wire to ground (-), does that very nicely and still doesn't provide a direct short for DC. To a completely ridiculous point, a bigger capacitor is better than a little capacitor when doing this. It can get a little 'sticky' if you let it, because how much AC/noise a capacitor will let get through is related to the frequency of that noise. There are formulas for that if you just have to know, otherwise, just use a higher value capacitor and don't worry about it. A sort of 'average' capacitance value for noise is something around 0.1 uF. If you wanna use a 1 farad capacitor, be my guest, but they get sort of expensive and dangerous. The other way capacitors are rated is by how much voltage they can handle. That's a real "iffy" thing if the voltage is not constant. If the voltage can surge, you want a cap that can handle that amount of surging voltage. So a minimum of 2 or 3 times the applied voltage is barely adequate, sort of. For 12 volt systems, a voltage rating of 50 volts is NOT too much by any means (especially for those 1 farad caps, even 100 volts wouldn't be too much). So look for capacitors that are at least 0.1 uF, @ 50 V. It may take more than one, or 2, just depends on the noise. Ceramic disk capacitors are very common in that size, and are cheap. There are polarized capacitors that can be much larger and cost a bit more, but they HAVE to be connected correctly or they certainly will pop no matter what the voltage ratings are. Stick with the ceramic caps, they can go either way (kinky, huh?).
Most cheaper line filters are just a bunch of capacitors in some kind of container. They work.
There's anothe electrical doo-hicky that can help. It's called a 'choke', and it lets DC through if and stops AC. A choke is just a sort of large coil. It has to handle all the current that whatever it's connected to will draw. That means that the wire used to make that coil is larger than you might think. The secondary windings of a 12 volt transformer are an example of that 'largeness'. The wire used is typically 10 to 100 times as large as the wire in the primary side of a transformer. that's one source for a choke if you happen to have a few dozen old transformers laying around. If not, then you can make them fairly easily, there's even a thingy about that on here somewhere.
A choke goes -in- the 'hot' (+) wire, NOT to ground. If you combine a capacitor and a choke you get what's called an 'LC' filter, and you will find them on just about every power supply that's filtered, all of them. So in effect, you are just adding a common power supply filter to your radio.
There ya' go, more than you ever wanted to know about filters. But it do come in handy, especially if you're as cheap as I am...
- 'Doc

believe it or not, but this was not too much for me. I appriciate you taking the time to type all that out. AT THE VERY LEAST I'm somewhat enlightened. But on a serious note I thank you again. That was very helpful. Hopefully I can get rid of that damn noise. All the locals know about getting rid of the noise is wiring directly to the battery which I've done scence the beginning anyway. I think it has to do with having an 83 for van. My friend says fords are very bad about this.

thanks again

Lt Dan · #7 10-22-2009, 05:50 AM

Quote:

Originally Posted by Beetle

For alternator noise, a lot of folks have had good luck with these:

New Page 1

Thanks for the link. I recon I'm gonna build one of these.

It looks cool.

I might build a few, a couple for some people who have helped me along the way but struggle with mild engine noise.

HEHE, thanks guys

mackmobile43 · #8 10-22-2009, 08:16 AM

Chevys used to have a large capacitor (condensor) bolted right on the back of the alternator for this very reason, well for the AM radios that where installed.

Lt Dan · #9 10-26-2009, 05:56 PM

Quote:

Originally Posted by Beetle

For alternator noise, a lot of folks have had good luck with these:

New Page 1

I don't know if its alternator noise because I built the above project and much to my dismay/disappointment the noise was un-affected.

What do I try next?

akforlife · #10 11-07-2009, 01:42 AM

It might be were your radio is hooked up. Try to change were the ground is mounted.
Ive had problems with alternator's sending noise into my stereo, mabye your alternator is the prob.

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Noise filter