Hiss in background, NOT hum.

[donc13]

I have a hiss in the background on my SDS200 it ONLY is heard over my bluetooth adapter->bluetooth earpiece. I do NOT hear it from the internal speaker nor do I hear it with a single earphone plugged into the front speaker jack. The Bluetooth adapter is USB powered plugged into into the USB A port on the front and a jumper from the front speaker jack to the audio input of the Bluetooth adapter. The hiss sounds Iike an open squelch hiss but if I open the squelch, I get a much louder hiss that does change level with the volume control.. The hiss does not increase or decrease in volume via the audio level (volume) setting. The actual audio from the scanner does go up and down with the volume setting. It's a minor annoyance, not that big a deal.

I have done the "hum" fix by Static Discharge. Again, zero hiss (or hum) from an earphone or the internal speaker.

My obvious guess is that it is generated by the usb powered bluetooth adapter or the audio jumper cable having some kind of impedence mis-match.

Anyone have any ideas on what could be causing this?

 

[nessnet]

Data noise?
Maybe try a ground loop isolator....(?)

 

[donc13]

Could be data noise but it's only heard thru the bluetooth link. Never hear it on the internal speaker or earphone plugged into the front earphone jack. Also, if it were data noise shouldn't its level change with the volume level?

Ground loop... anything is possible but they are all grounded thru the chassis... The earphone jack is plugged into the Bluetooth adapter and the Bluetooth adapter is plugged into the front USB type A port.

I haven't tried it yet hooked up in my RV via the 12v plug.

 

[Ubbe]

I have a hiss in the background on my SDS200 it ONLY is heard over my bluetooth adapter->bluetooth earpiece.

The important question are if you hear that hiss if you power off your scanner? It could be the BT device that has that noise.

If the noise stops then it could be too much sensitivity in the BT input. Test that by setting the scanner to a very low volume. Do you still have enough audio level at volume 3? When I use earphones plugged in the earphone jack of different scanners some of them output a very noticeable background noise and I have to use an adapter cable with a volume control on it to reduce the level until the noise are not heard and then adjust the scanners volume control.

/Ubbe

 

[donc13]

The important question are if you hear that hiss if you power off your scanner? It could be the BT device that has that noise.

If the noise stops then it could be too much sensitivity in the BT input. Test that by setting the scanner to a very low volume. Do you still have enough audio level at volume 3? When I use earphones plugged in the earphone jack of different scanners some of them output a very noticeable background noise and I have to use an adapter cable with a volume control on it to reduce the level until the noise are not heard and then adjust the scanners volume control.

/Ubbe

Turning off scanner also removes power from the Bluetooth adapter since it's powered by the front USB type A port.

No matter what the volume level is set at, I get the same level of hiss (relatively low), but I only get the hiss when the radio stops on a channel and squelch opens. During scanning, I get nothing.

 

[SteveSimpkin]

As a test, try powering the Bluetooth adapter with a separate USB power source like a USB phone charger. If the hiss disappears, then it could be a ground loop or noise issue with the SDS200 USB port.

 

[Ubbe]

You probably have earphones that you can plug in the scanner and compare to.

Some BT devices are sound activated, it only opens up when there's audio, a type of squelch. So if the BT itself are very noisy it will only show when it detects audio, like when the scanner receives a conversation.

Most BT devices have AVC, automatic volume control, that adjusts the volume depending of the level of the input signal. Maybe it's hard to hear, but is the hiss always at a constant level or does it change in volume depending of the voice level, less noise when they talk and more noise when they make a pause, indicating that the BT are too sensitive?

There are big differences between different bluetooth devices when it comes to how quick they open up for audio when used with a scanner and how much background hiss they have and other aspects that doesn't matter much when used with a cellular phone.

/Ubbe

 

[donc13]

As a test, try powering the Bluetooth adapter with a separate USB power source like a USB phone charger. If the hiss disappears, then it could be a ground loop or noise issue with the SDS200 USB port.

Tried external USB power source, no difference.

 

[donc13]

You probably have earphones that you can plug in the scanner and compare to.

Some BT devices are sound activated, it only opens up when there's audio, a type of squelch. So if the BT itself are very noisy it will only show when it detects audio, like when the scanner receives a conversation.

Most BT devices have AVC, automatic volume control, that adjusts the volume depending of the level of the input signal. Maybe it's hard to hear, but is the hiss always at a constant level or does it change in volume depending of the voice level, less noise when they talk and more noise when they make a pause, indicating that the BT are too sensitive?

There are big differences between different bluetooth devices when it comes to how quick they open up for audio when used with a scanner and how much background hiss they have and other aspects that doesn't matter much when used with a cellular phone.

/Ubbe

I think you hit it...

Using an external USB power source, no difference. Using a wired headphone, zero hiss.

BUT... the BT headphone has its own volume control and the hiss does go up and down with the BT volume controls. The volume of the hiss does not go up/down with the scanner's volume control. Only the voice volume goes up/down with the scanner volume. And, unless the BT adapter and/or headphone detect audio, I get nothing at all from the BT headphone.

So, I believe you are correct, it's the AVC combined with the BT "audio squelch" that is causing the hiss.

And the hiss is low enough in volume that it doesn't interfere with the voice. It's really only noticeable when a channel is keyed up, but no one is talking. While the hiss is still in the background when someone is talking (or a tone out is on) the voice itself isn't effected. It comes through clearly.


Thanks All!

 

[donc13]

OK, this is an old thread but there is an update.

So @nessnet suggested a ground loop isolator and they are cheap. So got one, tested it. It cuts the hiss some. Not much but it is noticeable. As before hiss volume does NOT change with SDS200 volume control but does change with the Bluetooth headphone volume control.

So... For $12 the ground loop isolator isn't a "fix" but it is a help and worth it.