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Interference coming from head unit in Jeep

SkylinesSuck

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SkylinesSuck Contributor

SkylinesSuck

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I noticed some constant noise breaking squelch on channel 17 with my old MXT275. Didn't think much of it. I recently swapped it out for a KG1000 and noticed it's receiving interference on several channels, worst on 17. It makes the rx light blink constantly without breaking squelch on some channels, and actually registers on the rx meter and breaks squelch on others. Strangely it even stops me from transmitting frequently, even though I have busy channel lockout disabled. I have narrowed it down to my double din wireless Android auto head unit. If I turn it off, interference disappears. Even when it's on but not putting out music, even with the sub off, even with the wifi turned off, it happens, even just in standby displaying the time.

 

I have grounded the piss out of the KG1000 to the body AND frame. I have installed literally 20 snap of ferrite beads of varying sizes (got an assortment for cheap on Amazon) on both the KG1000 as well as the head unit. I have also bonded the hood, body, exhaust, and frame. This interference happens even just in accessory with the engine off. I ran power cables for the KG1000 directly to the battery through an open window just to trouble shoot. No change.

 

Clearly the head unit is putting out some kind of interference. I double checked it's ground, but maybe it needs more? Any ideas?

 

I'm not having his luck with my radios lately. At least I have good swr on this one lol (1.3).

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serrasalmus Apprentice

serrasalmus

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have u shut off the blue tooth also? is it sat radio? with it being gone with a hard off then its def something in the head unit, could always try the tin hat method, could it be the digital fm receiver maybe try wrapping the antenna cable in said tin foil hat where the adapter more then likely is to go from a jeep to standard fm antenna. if your using the stock radio ground, why not try moving it to a good new location just to see the results? just throwing out ideas....good or bad is your call.........i take no responsibility if u blow up your jeep, blame that on the next door neighbors 

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Lscott Veteran

Lscott

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Sorry, the car stereo.

If in fact the noise is coming from the car stereo it's likely radiating from the wires between the speaker output and the speakers. Many new car stereos use Class D power amplifiers. To make it simple its a switching type circuit operating at high frequency, HUGE noise generators if not filtered. If the filtering is insufficient on the amp's output you can try putting your clamp on ferrites on the speaker wires right at the point where they exit the amplifier. You might even have to shield those wires and ground the shield right at the stereo.

 

https://www.analogictips.com/class-d-amplifiers-for-high-efficiency-switched-mode-sound/

 

The communications between the head unit and the main body is also likely using a fast serial communication protocol. One common protocol used extensively in automotive settings is the CAN bus. Those signals may also be a source of noise radiation and might need those clamp on ferrites too.

 

https://en.wikipedia.org/wiki/CAN_bus

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SkylinesSuck Contributor

SkylinesSuck

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Make sure you have a ferrite or two on ALL wires connected to the car stereo.

Especially the radio antenna cable.

I'm sure it's not easy to access these things but you have to do all the wires or it won't help.

 

Vince

I didn't know that, thanks. Just ordered another assorted pack of 20. I only had them on the power wires before.

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SkylinesSuck Contributor

SkylinesSuck

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If in fact the noise is coming from the car stereo it's likely radiating from the wires between the speaker output and the speakers. Many new car stereos use Class D power amplifiers. To make it simple its a switching type circuit operating at high frequency, HUGE noise generators if not filtered. If the filtering is insufficient on the amp's output you can try putting your clamp on ferrites on the speaker wires right at the point where they exit the amplifier. You might even have to shield those wires and ground the shield right at the stereo.

 

https://www.analogictips.com/class-d-amplifiers-for-high-efficiency-switched-mode-sound/

 

The communications between the head unit and the main body is also likely using a fast serial communication protocol. One common protocol used extensively in automotive settings is the CAN bus. Those signals may also be a source of noise radiation and might need those clamp on ferrites too.

 

https://en.wikipedia.org/wiki/CAN_bus

No CAN bus for me. 1998 ftw ☺️ I will make sure to get chokes on the speaker wires.

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tweiss3 Proficient

tweiss3

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And by remove the antenna I mean unscrewing the entire antenna off of it's nmo mount outside the vehicle.

 

Well, that just makes the GMRS radio deaf.

 

How close is this antenna to the FM antenna? What antenna are you using for GMRS? What is the model number for the Pioneer unit? I wonder if there is feedback up the FM antenna of some kind. I'd be interested to do some research on the model.

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OldRadioGuy Contributor

OldRadioGuy

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See what happens if you reconnect the GMRS antenna but disconnect the car stereo antenna.

It's very possible the stereo is radiating junk from its antenna.

 

If it's common mode radiation (which is likely) a ferrite on the stereo antenna coax will help.

 

This stuff can be very difficult to track down.

The car stereo is probably not even violating any RFI standards.

It's just so close that it doesn't take much.

 

Vince

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SkylinesSuck Contributor

SkylinesSuck

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Just for my understanding of principals here, wouldn't disconnecting the antenna and not receiving any interference point towards the interference coming in through the antenna i.e. broadcast interference and tell me it's not something coming through the power cables? I mean, no amount of grounding the radio out ferrite beads on the radio power wires will help, right? It's all about either filtering what the antenna receives or stopping the broadcast interference at it's source, right?

 

The antenna wire is not run anywhere even close to the head unit btw.

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tweiss3 Proficient

tweiss3

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No, removing the antenna just means the radio is receiving the signal, and it's not due to a direct contact on the coax. 

 

If you had a TinySA, you could remove the antenna from the receive port and start getting it closer to spots around/on the head unit to see where the signal is radiating from.

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