SDS100 hum on MSP

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murphcc1
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SDS100 hum on MSP

Post by murphcc1 »

So I have a hum on my SDS100.
I DO NOT have a hum outside of that, there is no hum when not in the car.
I have it in my car, I use a 3.5mm cord from unit to the AUX input for radio.(It's not RFI)
I ONLY get a hum while on the MSP trunked system.
I do not get any hum on any other conventional freqs.

What I am missing??

jbella
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Re: SDS100 hum on MSP

Post by jbella »

murphcc1 wrote:
10 May 2021 17:31


What I am missing??
The words?

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W1KNE
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Re: SDS100 hum on MSP

Post by W1KNE »

murphcc1 wrote:
10 May 2021 17:31
So I have a hum on my SDS100.
I DO NOT have a hum outside of that, there is no hum when not in the car.
I have it in my car, I use a 3.5mm cord from unit to the AUX input for radio.(It's not RFI)
I ONLY get a hum while on the MSP trunked system.
I do not get any hum on any other conventional freqs.

What I am missing??
You're missing figuring out what is causing an electrical hum (aka interference) over the voice channels of MSP in your car.

Most likely cause is the sparkplugs, which can often generate high frequency noise that goes well into the satellite bands.
Mike Fitzpatrick
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Owner: Scan New England - NECRAT.US
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ScanBoston
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Re: SDS100 hum on MSP

Post by ScanBoston »

Take your sparkplugs out and see if it goes away! : )

murphcc1
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Re: SDS100 hum on MSP

Post by murphcc1 »

It's constant hum, nothing to do with RFI as stated.
The hum does not go with the speed of the engine.
And it's only on the MSP trunked system, all other freqs dont have the hum.
I'll see about getting some audio of it and post it.

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Citywide 173
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Re: SDS100 hum on MSP

Post by Citywide 173 »

Alternator whine and spark plugs causing RFI are two different things. Is the hum there with the car off? Do you have any other analog 800 Mhz trunked systems in the radio? If so, is there anything present on those while in the car?

EDIT:

Are you powering the unit from a cigarette lighter to USB adapter? Those are notorious for RFI on higher frequencies.
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murphcc1
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Re: SDS100 hum on MSP

Post by murphcc1 »

Th engine off, there is the hum..........NO alternator whine or spark plug noise!!
being powered by USB power plug in car, speaker connection is through 3.5mm male to male plug into the AUX input.

I'll change power from what I have to try the USB directly in car, removing the cigarette lighter thingy........

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W1KNE
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Re: SDS100 hum on MSP

Post by W1KNE »

If you unplug from the car's sound system (aux input) does the hum go away?
If you run on battery vs the charger?
Mike Fitzpatrick
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murphcc1
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Re: SDS100 hum on MSP

Post by murphcc1 »

Yes, the only time it hums is when it's on the AUX input in the car.
It does not make the hum any other time, whether the power cord is connected or not.

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Scott
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Re: SDS100 hum on MSP

Post by Scott »

Ground loop. Google that and then find a suitable ground loop isolation circuit to put in line. This is a relatively common occurrence.
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murphcc1
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Re: SDS100 hum on MSP

Post by murphcc1 »

when it hits on the MSP broadcast you can hear the hum, although it's not all that clear on the video, it's quite pronounced in person.
https://youtu.be/5LJ-KTS2gMc

murphcc1
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Re: SDS100 hum on MSP

Post by murphcc1 »

WEll, just found something on my SDS 200 in my house, when I turn up the volume I can hear that same HUM in the back ground, apparently my car amplifies it.
Couldn't hear it when volume low.

So now gonna check on the SDS100 in the car...........seems like it's always there but couldn't hear it till I increased the volume and it's amplified in the car stereo.

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schwab
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Re: SDS100 hum on MSP

Post by schwab »

It seems like the speakers in the car are amplifying the sub-audible data that's transmitted on a Moto Type 2 system. It seemed like it went away when you unplugged the aux cable from the scanner in the video. I notice the same thing with PL tones being audible when I listen with headphones or with an aux cable in the car.
Edited to add: try listening with headphones, I bet it will do the same thing.
Jacob
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murphcc1
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Re: SDS100 hum on MSP

Post by murphcc1 »

YUP...thats it......tried the earphones, hear that hum with them on........

All done!!

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