Really WEIRD scanner / computer speaker behavior

Status
Not open for further replies.

Tim-B

Member
Joined
Nov 17, 2016
Messages
397
Location
Lafayette, LA
Okay, so I have a BCD436HP connected via a usb cable to a laptop running ProScan and I have it setup to look for new previously unidentified talkgroups on a 700 MHz trunked system. The 436 also has a wire from its headphone jack to the laptop's mic input so it can record traffic on any new talkgroups found. I also have a set of speakers connected to the laptop. Ok, so far so good. Now I also have a 396XT running by itself on batteries - no wires connected to anything and it is monitoring known talkgroups on the same system. Okay, with me so far?

Now, here is the weird part:

When the 396 receives a talkroup I can faintly hear that traffic on the computer speakers that are plugged into the laptop. The 436 which is actually connected to the laptop is NOT receiving this talkgroup but is sitting there silently while looking for new talkgroups. If I turn the computer speakers all the way up I can hear the 396's talkgroup clearly and at the end of the transmission I get this weird echo with reverb effect that fades out as it repeats like:

"Are you at the station the station the station the station the station the station the station?" with each "the station" being a little lower in volume unitl it fades completely. Then there this high pitched whine like feedback between a speaker and mic too close to each other begins and gets louder and louder until I turn the speaker down.

Now remember the 396 is not connected to anything by wires. It is on its own running on batteries. Only the 436 is connected to the laptop and it is not receiving that talkgroup because it is looking for new unidentified talkgroups.

Any ideas on what it going on?
 

K9DAK

Member
Premium Subscriber
Joined
Dec 16, 2010
Messages
538
Location
Wauconda, IL
Does the laptop have a built-in internal microphone that you need to disable in the audio controls?
 

Tim-B

Member
Joined
Nov 17, 2016
Messages
397
Location
Lafayette, LA
Well, ok that is what was doing it. It seems I didn't have the microphone cable from the scanner plugged in all the way so when ProScan activated the microphone it used the built in microphone on the laptop's monitor frame instead of the jack where the cable from the scanner plugs in. When I pushed the cable in all the way the feedback stopped. So what was happening is the built in mic was picking up the speaker of the 436 unitl I pushed the wire in all the way into the jack.
 

jonwienke

More Info Coming Soon!
Premium Subscriber
Joined
Jul 18, 2014
Messages
13,363
Location
VA
You should be connecting the 436 to the line-in on the computer, not the mic input. The mic input is far more sensitive to stray voltage and interference and is not designed to properly handle the output signal from the 436. That will reduce the crosstalk interference by a factor of 1000 or so. Also, you probably have some cheap cables that aren't very well shielded. Upgrading to better cables with better shielding will also help. Doing both should completely eliminate the problem.
 
Joined
Dec 19, 2002
Messages
201
New computers are crap- one 3.5mm jack and you have to tell it if you want it to be a mic in, a line-in a speaker out, a line out, etc... why not just 2 or 3 jacks- yes it would cost an extra $1.50, but it would be worth it, IMO.
 

cmdrwill

Member
Joined
Mar 30, 2005
Messages
3,969
Location
So Cali
You need a transformer/line isolator in the scanner speaker to computer. Or at the least an attenuator impedance matcher.
 

mule1075

Member
Feed Provider
Joined
Jan 20, 2003
Messages
3,892
Location
Washington Pennsylvania
You should be connecting the 436 to the line-in on the computer, not the mic input. The mic input is far more sensitive to stray voltage and interference and is not designed to properly handle the output signal from the 436. That will reduce the crosstalk interference by a factor of 1000 or so. Also, you probably have some cheap cables that aren't very well shielded. Upgrading to better cables with better shielding will also help. Doing both should completely eliminate the problem.
Since most laptops as he has does not have a line in your post does not hold water.Mic in does work it is all in the settings.

Sent from my SM-S907VL using Tapatalk
 

Tim-B

Member
Joined
Nov 17, 2016
Messages
397
Location
Lafayette, LA
Well, I checked all sides of the laptop and it only has two audio jacks. One for speaker and one for microphone. But it is working fine now that I actually pushed the plug in all the way.
 

jonwienke

More Info Coming Soon!
Premium Subscriber
Joined
Jul 18, 2014
Messages
13,363
Location
VA
Since most laptops as he has does not have a line in your post does not hold water.Mic in does work it is all in the settings.
Sorry, but you don't know what you're talking about.

Mic in expects a millivolt-level signal. Giving it a headphone-level signal (which can be 1 volt RMS or more) will result in noisy, extremely distorted output and can damage the input, because the input signal is about 1000x higher than the input expects.

Line-level input expects an input signal of about 1-volt. A headphone jack can exceed this somewhat, but you can match it reasonably well with the output volume control of the signal source.

If the OP's laptop is the one-jack variety, then the function of the jack can be selected in software. It's possible there may be a auto setting, and the scanner output may be auto-detected as a line-level signal. If so, the OP got lucky in that the default jack setting is line-level input or a reasonably working auto-detect. But that's luck, not good practice.

You should never deliberately connect a headphone or speaker level output to a microphone level input. Always verify that the input is configured to handle line-level signals before connecting a headphone output.
 

mule1075

Member
Feed Provider
Joined
Jan 20, 2003
Messages
3,892
Location
Washington Pennsylvania
Sorry, but you don't know what you're talking about.

Mic in expects a millivolt-level signal. Giving it a headphone-level signal (which can be 1 volt RMS or more) will result in noisy, extremely distorted output and can damage the input, because the input signal is about 1000x higher than the input expects.

Line-level input expects an input signal of about 1-volt. A headphone jack can exceed this somewhat, but you can match it reasonably well with the output volume control of the signal source.

If the OP's laptop is the one-jack variety, then the function of the jack can be selected in software. It's possible there may be a auto setting, and the scanner output may be auto-detected as a line-level signal. If so, the OP got lucky in that the default jack setting is line-level input or a reasonably working auto-detect. But that's luck, not good practice.

You should never deliberately connect a headphone or speaker level output to a microphone level input. Always verify that the input is configured to handle line-level signals before connecting a headphone output.
Whatever you say you seem to know more then anybody else even the engineering of the scanners.The OP found the solution to his problem.I am done here.

Sent from my SM-S907VL using Tapatalk
 
Status
Not open for further replies.
Top