FM interference / signal degradation

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FM interference / signal degradation

Postby plantone » Mon Aug 07, 2017 10:52 am

i recently got a MIFI to use as a dedicated hotspot in my truck for my android indash for the navigation.

i mounted it up on the B pillar, above the seatbelt pivot, and snaked a USB cable behind the plastic for charging.


since i had both battery power and a turn on wire back behind the rear seat for the amp, i picked up a under dash USB power port ( http://a.co/1BBlzUK ) and wired it up on a relay i had ( http://a.co/2PH3uKM ) so that it would only charge when the vehicle was operating.


however - my FM signal is getting some bad interference when the MIFI jet-pack is plugged into the USB. As soon as i unplug it, goes away immediately.

i fused both the always on power and the turn on wire pre-relay with an inline mini fuse to protect everything in the event of any kind of a ssurge. i put a 5amp fuse on the turn on wire, and a 10 amp on the battery feed. everythings grounded through the ground block that feeds the amp (i had a pair of power distribution blocks installed back there when the amp/sub got put in)


so i'm wondering what my options are to correct this - short of plugging and unplugging the MIFI as needed.


do i switch the relay to the white wire (87a?) and have it charge when the vehicle/radio is off? (i'd rather not go there, but it would be a 2 minute fix)
will a ferite core noise suppressor fix it? ( http://a.co/dGmKu0q ) if so which wire does it go onto - i'm guessing the blue turn-on wire going to the radio?


#ihate12v :mrgreen:
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Re: FM interference / signal degradation

Postby ApproachMedium » Sun Sep 17, 2017 8:10 am

Is it on the passenger side or driver side b pillar? It sounds like the MIFI box is interfereing with the ground plane of your vehicle when its ground plane is attached to your vehicle via the USB ports ground. You may need to try a different location, maybe in the center of the truck like the center console.
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Re: FM interference / signal degradation

Postby plantone » Tue Sep 19, 2017 10:21 am

its on the passenger side b-pillar, right at the top of the plastic before you get to the headliner.

here's my ignorance showing itself - how would moving the hotspot to another location change whats happening if its a ground related issue? the power supply's ground point would not be changing. is it some kind of EM emission causing the problem you think based on the proximity to the metal directly under the b-pillar plastic? or is it a possible issue with shielding (or lack of) with the USB cable itself based on its proximity to the frame behing behind the plastic?

i'll try a different cable today and relocate the hotspot and see if it goes away.
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"Your mother was a hamster, and your father smelt of elderberries" - The French Fellows
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Re: FM interference / signal degradation

Postby ApproachMedium » Thu Sep 21, 2017 8:26 pm

yea id try to go for a higher end usb cable with shielding. it may be the cable itself thats creating an "antenna" and inducing the noise into the FM antennas ground plane. Moving the box could help, i had an issue with my shallow sub for my volkswagen causing FM interference if my amp was on. the large diameter of the voice coil in the sub being too close to my rear window glass which had the Fm antenna in it was enough to screw it up. I tried putting a ground loop RCA isolator between the amp and the radio but that did not change anything. i had to change the position of the sub in my trunk to clear it up.
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Re: FM interference / signal degradation

Postby plantone » Tue Sep 26, 2017 11:39 am

ok so i tried a different cable and moved the location of the wifi hotspot to the middle of the truck. in fact it was sitting on the center console.

no change. signal interference with the mifi charging, soon as i unplug it - nothing.


this is not causing interference any other time other than when the WIFI is plugged in and physically charging.



i'm fairly comfortable its not the sub as again, this issue only presents itself during charging of the MIFI, no other time.
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Re: FM interference / signal degradation

Postby ApproachMedium » Wed Sep 27, 2017 9:28 am

Oh its def the MIfi, I just made the reference to the issue i had with my sub in the VW because it did something similar. When i mentioned move the box, i meant the mifi. So it seems to be there is a ground loop issue with plugging the Mifi in and charging. Does it cause any interference on your stereo on any other functions? Or just FM?
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Re: FM interference / signal degradation

Postby plantone » Sat Oct 28, 2017 8:06 am

just the FM signal. nothing else.

i had a conversation with a tech at crutchfield about it, and his only guess is that it may be causing an amperage drop on the powered antenna. which i guess is possible if the minion who hooked the radio up used the wrong wire to feed the amp turn on, or the same feed comes out of the radio for the antenna and the amp turn on and they just put a Y in there so it feels like theres actually two wires in play. although i would think that it would be an issue anytime then, since that same turn on wire is only triggering my relay, which draws in the milliamps range right?

i may have to pony up and just run another wire off the ignition circuit back there instead, which i was trying to avoid doing by just tapping the turn on wire thats already back there.

its just wonky enough to piss off the pope.
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Re: FM interference / signal degradation

Postby ApproachMedium » Tue Oct 31, 2017 6:43 pm

Aftermarket radios dont come with power antenna up outputs, they come with a remote power on wire. The s10 factory radio doesnt have either. The remote wire would only activate when the radio is powered on, not ignition.

Is the buzzing coming from all speakers or just whats run off your amp?
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Re: FM interference / signal degradation

Postby plantone » Thu Nov 02, 2017 8:03 am

i guess i should have said amplified antenna, its not a power up/down type antenna. the guy i spoke with at crutchfield said most/all gm's use them.


its not a buzzing noise. its a signal loss issue - i get static, or the signal fades in/out like you're right on the edge of a stations broadcast range. if i unplug - perfect signal again.


as such, its in all the speakers.




what i meant was, re ignition circuit, i was thinking about tapping an ignition on circuit to feed power back to the relay for the socket, instead of using the turn-on wire from the radio thats feeding the amp to trigger it.

altho if i did it that way i could probably just feed it from the ignition on circuit directly, and eliminate the need for the relay in the first place.
"Politics: The art of appearing candid and completely open while concealing as much as possible." - Frank Herbert

"Your mother was a hamster, and your father smelt of elderberries" - The French Fellows
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Re: FM interference / signal degradation

Postby ApproachMedium » Thu Nov 02, 2017 11:06 pm

These S10s, unless the antenna is amped internally in the factory radio, do not have any external antenna amplifiers. And yes that sounds like a signal loss issue for sure, so it has nothing to do with any external speaker amps.

Yea i dont think you need the relay, but isnt the cig lighter hooked to ignition on anyways? I know the two accesory ports are always hot.
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Re: FM interference / signal degradation

Postby plantone » Sun Nov 05, 2017 10:01 am

in my truck the cig lighter and the acc port are always-on. i'm always yankin the cord to turn off the fuzzbuster
"Politics: The art of appearing candid and completely open while concealing as much as possible." - Frank Herbert

"Your mother was a hamster, and your father smelt of elderberries" - The French Fellows
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Re: FM interference / signal degradation

Postby plantone » Sun Nov 05, 2017 10:09 am

i'm gonna see if powering the relay from the main feed and not the turn on wire makes a difference. maybe that'll help me narrow down where the problem is.
"Politics: The art of appearing candid and completely open while concealing as much as possible." - Frank Herbert

"Your mother was a hamster, and your father smelt of elderberries" - The French Fellows
--------------------------------------------------------------------------------------------------

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Re: FM interference / signal degradation

Postby ApproachMedium » Mon Nov 06, 2017 7:32 pm

plantone wrote:in my truck the cig lighter and the acc port are always-on. i'm always yankin the cord to turn off the fuzzbuster



Interesting, i used for a while the cig ligher power to run my old bazooka tube because it only needed 10A and i thought it was switched. I guess ill have to check with a meter. The new one needed a hard line with more amps, so i switched it.
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