996XT and Grounding

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tatanka01

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The manual says:

" WARNING!

Never connect any part of the headphone jack to the antenna jack or connect the radio to an installation where the antenna and audio connection are grounded. This might also damage the scanner. "

I'm not sure how to read this. Aren't most antennas and audio connections grounded on one end?
 

Viper43

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You can ground the chassis, and an external antenna can be grounded but you cannot run a ground to the headphone jack or it WILL damage the scanner. The headphone jack is grounded but in other models a mod was used that grounded the headphone jack TO the scanners antenna connector to boost audio, doing that with the 396's will damage the scanner.
 

jackj

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I honestly don't have any idea what they are saying. Like most manuals written by people who's first language isn't English, it is hard to figure out what they mean. You are right in that most headphone jacks have the sleeve connected to ground and most external antennas are connected to ground. The sleeve of my 996T's headphone jack is connected internally to the shield of the antenna. Some antennas will have DC continuity from both the shield and the center conductor to ground. That they might be talking about the tip of the headphone jack, grounding that would short out the audio and might overload the audio output IC. They might also be cautioning you not to use the headphone jack as a connection to an external ground as a lightning strike to the antenna would cause high current to flow through the PC board and damage the scanner. But a lightning strike to an ungrounded scanner would damage it also. I wouldn't worry about it, it's probably 'lawyer-speak' for CYA.
 

tenthirtyone

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Floating Ground

I believe what is happening here is known as a "floating" ground.

In years past car stereos allowed the (-) terminal of the speaker leads to make contact / or utilize the body ground of the vehicle. One could run one wire (+) to the speaker and simply run a short (-) lead to the closest area of the car body and all would work fine.

Most newer mobile audio installations involve a "floating" ground. In this configuration the body / chassis ground that powers the unit is separate from the (-) speaker leads. The speaker(+) and (-) leads must be run to each speaker and can not contact the body / chassis or "damage will occur".

Sounds like a "floating ground" system at work here. You can have the chassis of the scanner grounded, as well as the outer braid / ground plane of the antenna. But do not ground or connect the (-) leg of the headphone / speaker out to the chassis ground.

My 2 cents.
 

jackj

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Ground

I believe what is happening here is known as a "floating" ground.

In years past car stereos allowed the (-) terminal of the speaker leads to make contact / or utilize the body ground of the vehicle. One could run one wire (+) to the speaker and simply run a short (-) lead to the closest area of the car body and all would work fine.

Most newer mobile audio installations involve a "floating" ground. In this configuration the body / chassis ground that powers the unit is separate from the (-) speaker leads. The speaker(+) and (-) leads must be run to each speaker and can not contact the body / chassis or "damage will occur".

Sounds like a "floating ground" system at work here. You can have the chassis of the scanner grounded, as well as the outer braid / ground plane of the antenna. But do not ground or connect the (-) leg of the headphone / speaker out to the chassis ground.

My 2 cents.
Yes, high powered audio systems do use what you might call a floating ground on the audio. They use two high powered audio power amps connected and driven in a push-pull arrangement. Both sides of the audio are above ground and 180 degrees out of phase. But that doesn't apply to my 996T, the headphone jack IS connected to the antenna shield internally or through the case of the scanner. I can't speak for the 396 as I don't have one to check, maybe someone else could check one and post the results here.

I wonder if the Uniden 20w amplified speaker's phono plug sleeve is grounded?
 
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