BC125AT: Question about a warning that’s in the manual for a BC125AT.

[corneileous]

Hopefully this is the right spot for this question but being that I’m going to start using this little scanner at home for a while since it has more updated technology over my ancient BC8500XLT, what does the warning below mean? I have an external speaker that I’m going to use with it and I will have my outside roof-top antenna coax connected to it but I have no idea what this is warning me…lol.

WARNING! If you connect an external speaker to the scanner's headphone jack, never connect the audio output line to a power supply and ground. This might damage the scanner.

 

[alwayslistening]

I believe it may be because the two audio output connections are actively driven by the audio output amplifier. I think this is why, when you plug a set of stereo headphones into the headphone jack, you are able to hear audio in both the left and right earpieces.

In other radio designs, one audio output connection, usually the sleeve contact on the audio plug, is often connected to ground which is usually the negative contact on the battery or external DC power supply. The other, usually the tip of the audio plug, is driven by the radio's audio amplifier. But in Uniden's case, the sleeve contact is also driven by the audio amplifier, so connecting it to ground or power will likely damage the audio amplifier.

If your speaker is completely isolated from the antenna connection and any external DC power supply input, this warning is an "n/a" for you. But if you plan to connect the scanner's headphone jack to, say, an external audio amplifier, then you will need to DC isolate the headphone jack's two output connections from the audio amplifier. This can be easily accomplished by installing an audio isolation transformer between the scanner's headphone jack output and the audio amplifier's input.

 

[corneileous]

I believe it may be because the two audio output connections are actively driven by the audio output amplifier. I think this is why, when you plug a set of stereo headphones into the headphone jack, you are able to hear audio in both the left and right earpieces.

In other radio designs, one audio output connection, usually the sleeve contact on the audio plug, is often connected to ground which is usually the negative contact on the battery or external DC power supply. The other, usually the tip of the audio plug, is driven by the radio's audio amplifier. But in Uniden's case, the sleeve contact is also driven by the audio amplifier, so connecting it to ground or power will likely damage the audio amplifier.

If your speaker is completely isolated from the antenna connection and any external DC power supply input, this warning is an "n/a" for you. But if you plan to connect the scanner's headphone jack to, say, an external audio amplifier, then you will need to DC isolate the headphone jack's two output connections from the audio amplifier. This can be easily accomplished by installing an audio isolation transformer between the scanner's headphone jack output and the audio amplifier's input.

OK so, this doesn’t apply to me if I use an external powered speaker plugged into the headphone jack? But I guess to and all confusion, what amplified speaker can I use with this little handheld scanner that won’t mess it up? A while back, I bought a cheap little extension speaker from Walmart that really wasn’t all that great that worked well with my dinosaur BC8500XLT but when plugged into this little portable scanner, you can’t even hear anything even with the volume turned all the way up.

 

[alwayslistening]

This warning does not apply if you are using a *non-amplified* (i.e. the speaker does not require power) external speaker and that speaker is otherwise not electrically connected to the scanner, i.e. the speaker and, if in use, an external antenna do not share a common connection, such as the speaker and antenna being electrically connected to the chassis of a vehicle. The risk is if there is a path for either of the two electrical contacts on the audio output jack of the scanner coming in contact with the antenna connections, or if the scanner is externally powered, to the DC power input contacts of the scanner.

It's a bit esoteric, and it took me a bit to figure it out since I have scanners which are connected to external DC power, external antennas and feed into computer audio inputs. Safest bet is to use an isolation transformer on the scanner's audio output.

 

[alwayslistening]

This article does a much better job of describing the issue than I can:

SDS100/SDS200: - Question about SDS200 external speaker jack configuration

I have a question about the external speaker jack on the Uniden SDS200. I am trying to find out what the configuration is. From the several radios I use, the external speaker jack is monaural using the tip and sleeve (T/S) configuration. The tip is the audio signal and the sleeve is at the...

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