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Vehicle RFI help needed

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#1
I have a 95 Dodge ram 1500, with a tyt-9800 Tri-Band radio. The power lead comes directly from the battery with a in-line fuse directly at the terminal. At the radio end, I have a noise filter that connects to the radio power, and ground. The antenna in mounted on the roof, with a 3/4" hole drilled, and routed through the headliner and down the backside of the truck away from any powered lines. I have no issues with the vehicle being off, but one I start the vehicle can hear wine in the radio, on mainly on the VHF range, but I get some noise on the UHF range. Would like some help to eliminate the noise, or where to start on tracing down were its coming from.
https://gyazo.com/8d8f461f27fd02519e80377ac96d172a
 
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#2
Couple of question:
Is the whine coming through the speaker, or is it just on your transmit signal?
Where is the negative power lead connected?
Is the radio chassis grounded?
Does the whine change pitch when you rev the engine?
Does the whine change pitch with the HVAC blower?
 
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#3
Couple of question:
Is the whine coming through the speaker, or is it just on your transmit signal?
Where is the negative power lead connected?
Is the radio chassis grounded?
Does the whine change pitch when you rev the engine?
Does the whine change pitch with the HVAC blower?
Through the speaker. My transmissions are clear as day.
Negative is ground under the carpet on the body of the vehicle.
The radio chassis where it is mounted, uses to self tapping screws into the floor of the vehicle. Nothing else was used. What would be the best way to make sure its grounded?
I believe so, will double check next time I get out in my truck.
No change with the HVAC blower.
 
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#4
Sounds like alternator whine, especially if it changes when you rev the engine. I had a GMC pickup that would do that. I moved the negative power lead off the battery to the vehicle body, and it fixed it.

Might be your alternator starting to go. If it's the original one, it might be worth getting it checked.

Make sure your ground connections are clean, as in shiny metal.
I usually run a separate ground strap from the radio chassis to the vehicle body. I've had issues with flakey grounds before, and an ounce of prevention is worth a pound of cure.
 
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#5
Is it a powered speaker?
It can be due to the fact that the radio and speaker are powered by the same source.
They make an isolator for that. I forget what it is called, but they are only a few $$ on Amazon.
Also, I don't know where the speaker and radio are mounted. They need to be away from the dash.
 
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#7
Does the noise go away if you disconnect the antenna?
Yes
Is it a powered speaker?
It can be due to the fact that the radio and speaker are powered by the same source.
They make an isolator for that. I forget what it is called, but they are only a few $$ on Amazon.
Also, I don't know where the speaker and radio are mounted. They need to be away from the dash.
Its a RoadPro RPSP-15 Universal CB Extension Speaker. No power needed.

Sounds like alternator whine, especially if it changes when you rev the engine. I had a GMC pickup that would do that. I moved the negative power lead off the battery to the vehicle body, and it fixed it.

Might be your alternator starting to go. If it's the original one, it might be worth getting it checked.

Make sure your ground connections are clean, as in shiny metal.
I usually run a separate ground strap from the radio chassis to the vehicle body. I've had issues with flakey grounds before, and an ounce of prevention is worth a pound of cure.
Just cleaned up the connections that go to the body. They have a good ground, but still no luck. I seem to have a good ground coming from the chassis to the body, because I had removed the ground wire to reconnect it and the radio was still powered on. Might order a ground strap to try out.
 
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#8
If disconnecting the antenna makes the noise go away, then it's not a power supply issue, it's an RFI issue, and messing around with ground wires is unlikely to help.

What you need to do is get one of those inexpensive SDR dongles, a VHF HT antenna, a USB extension cable, and a laptop.

Install SDR# on the laptop (it's free), attach the HT antenna to the SDR dongle, and then plug the SDR dongle into the laptop with the USB extension cable so you can move it around. You now have a RF sniffer. With the SDR tuned to the most troublesome VHF frequency, walk around the vehicle with the hood and doors open, and poke the SDR & antenna into every compartment and nook and cranny to see where the noise signal is strongest. That will tell you where the RFI is coming from, and hopefully give you an idea of how to fix it.

If the alternator is generating the RFI, it probably needs to be replaced.
 
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#9
One question that hasn't been asked here is what shape is the battery in? I ask this question because as a battery ages, it's internal resistance goes up. When this happens, it no longer has the ability to act as a filter to any noise the alternator might generate. A battery over 3 years old or so is getting down on it's ability to work properly. This will show up more in the cold of winter or the heat in the summer.

Having said this, if the battery is over 3 years old, you might start to notice some suttle things starting to happen. Like the engine is cranking slower than it use to. Now and then the clock in the dash will get set back to midnight when you go to start the engine. The lights will seem to dim some when you turn the A/C fan on high at night. When you pull up to a stop light at night, the headlights seen to dim down when the engine speed goes to the idle speed.

You can do some simple tests with a digital volt meter.
1. Before you start the engine first thing in the morning, measure the battery voltage and write it down.
2. Next start the engine and measure the battery voltage.
3. Now turn on the headlights on low beam, measure the voltage.
4. Next, turn the headlights to high beam, measure the voltage.
5. Now turn on the A/C on low fan speed and measure the voltage.
6. Put the fan speed on high and measure the voltage.
7. Turn on your windshield wipers, measure the voltage.

Some place along the line here, you might see the battery terminal voltage drop. That's OK. You are trying to see just what capacity the alternator has to keep the voltage up.

The other test you need to do is put your digital meter in the AC scale and measure the battery voltage, but in AC millivolts. This is going to show if all the diodes in the alternator are working. A bad diode will show up as a ripple in the DC voltage and can only be measured in the AC voltage mode. It won't be a whole lot. Maybe below 100 millivolts in most cases. The whine you may be hearing is the AC voltage on the DC wiring.

Good luck on your testing.
 
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#12
Well, that only changes everything then. :D

In that case, it isn't RFI, and voltage ripple from the alternator is a prime suspect.
 

popnokick

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#13
Noting that the noise DOES NOT go away when you disconnect the antenna puts all of the DC power supply components (and alternator whine) back into consideration. Having a noise filter in the 12VDC line is a good idea HOWEVER the one you have (shown in the linked picture) is suspect. I would replace it with a similar filter (not necessarily Radio Shack - many options available)... the one shown may have failed. Another possibility is that the ground connection to the noise filter is not good. You should be able to verify that with a multimeter.
 
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#14
Noting that the noise DOES NOT go away when you disconnect the antenna puts all of the DC power supply components (and alternator whine) back into consideration. Having a noise filter in the 12VDC line is a good idea HOWEVER the one you have (shown in the linked picture) is suspect. I would replace it with a similar filter (not necessarily Radio Shack - many options available)... the one shown may have failed. Another possibility is that the ground connection to the noise filter is not good. You should be able to verify that with a multimeter.
Was thinking about replacing the noise filter at one point. The one im using now was actually in the truck when I purchased it. So Im not sure how old it is.
 
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#15
Was thinking about replacing the noise filter at one point. The one im using now was actually in the truck when I purchased it. So Im not sure how old it is.
I've never had to use one. When I've had issues, I've preferred to resolve it rather than hide it. If it is your alternator, finding out now is better than being left on the side of the road. Many auto parts stores will test them for free.
 

DJ11DLN

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#16
I had a '95 Dodge pickup for years and I went through all of the usual things mentioned here trying unsuccessfully to eliminate the alternator noise. A new alternator did not work either, so I returned it and took my old one to a professional rebuilder I've used for 30+ years. He rebuilt it but said I was going to get "radio noise" regardless due to it being what he termed as "a poor design." It was slightly better after he got through with it.

After trying some over-the-counter filters with little or no improvement I wound up building one from online plans. It's not coming up in a quick search and I've lost the link (which may be dead anyway as it's been YEARS) but if you just google "DIY alternator whine filter" you will get a bunch of very similar designs. Look for something with a good-sized ferrite core (I used a large repair link) and a big capacitor. The one I built was rated for 25A, I ran scanners and a 2-way with it for years with good results on both TX and RX.
 
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#17
Just had my alternator tested, bad voltage regulator. I believe that will be the problem im having.
Now taking donations for a new one :)
 
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