BCD436HP/BCD536HP: BCD536HP connecting external antenna cuts out audio output

[rleonard10]

I recently replaced an old external antenna I had connected to the Uniden BCD536HP. When I connect this new antenna the auxiliary audio output jack stops working. I used an existing cable that was running to a different location for my new antenna so it isn't the same cable the old antenna used to connect the scanner and wasn't sure if the cable is bad if that would cause this issue or not? If I disconnect the auxiliary audio output the internal speaker of the scanner works. Has anyone ever heard of this happening?

 

[n1chu]

Te aux audio output jack and the antenna input shouldn’t create any ill affects on each other. I’d first check your external speaker for breaks in the line. Do you have another external jack you can try?

 

[KevinC]

I recently replaced an old external antenna I had connected to the Uniden BCD536HP. When I connect this new antenna the auxiliary audio output jack stops working. I used an existing cable that was running to a different location for my new antenna so it isn't the same cable the old antenna used to connect the scanner and wasn't sure if the cable is bad if that would cause this issue or not? If I disconnect the auxiliary audio output the internal speaker of the scanner works. Has anyone ever heard of this happening?

Are you sure that existing coax actually goes to the antenna? It sounds like it may have voltage on it.

 

[n1chu]

Te aux audio output jack and the antenna input shouldn’t create any ill affects on each other. I’d first check your external speaker for breaks in the line. Do you have another external jack you can try?

That should have read Do you have another external SPEAKER you could try?

 

[rleonard10]

Are you sure that existing coax actually goes to the antenna? It sounds like it may have voltage on it.

Yeah the wire is one that went to a low band antenna we had and traced it down off the tower to where it terminated. I believe it is LMR400.

 

[rleonard10]

That should have read Do you have another external SPEAKER you could try?

I will see if I can dig up another speaker. The way the system currently is the external audio jack goes to an amplifier and is then transmitted to the speakers in our firehouse. When I reconnect the old antenna we had on everything works fine.

 

[jtwalker]

I will see if I can dig up another speaker. The way the system currently is the external audio jack goes to an amplifier and is then transmitted to the speakers in our firehouse. When I reconnect the old antenna we had on everything works fine.

Process of elimination leaves ... something is wrong with "new cable" or "new antenna".

 

[rleonard10]

Process of elimination leaves ... something is wrong with "new cable" or "new antenna".

That is what I am thinking. I have ordered a new cable to try.

 

[jtwalker]

That is what I am thinking. I have ordered a new cable to try.

It is really an odd symptom.

 

[KevinC]

It is really an odd symptom.

I suspect a ground loop. Maybe the "other" coax is connected to the grounding system and it has an issue. I would do some voltage checks or contact an electrician. Please be careful with this.

 

[n1chu]

Ditto what KevinC said. Be very careful. Somehow that second coax is affecting the scanner… a connection where none should exist may be present. The fact you are using an amplifier means you are using an “active” external speaker system. An active system requires a power source. That second coax might be somehow intertwined with that amplifier on the aux speaker line. You also state “the external audio jack goes to an amplifier and is then transmitted to the speakers in our firehouse”. I question your use of the word transmitted. Can we substitute “wired” for “transmitted”? Or are you using some type of wireless connection?

 

[rleonard10]

Ditto what KevinC said. Be very careful. Somehow that second coax is affecting the scanner… a connection where none should exist may be present. The fact you are using an amplifier means you are using an “active” external speaker system. An active system requires a power source. That second coax might be somehow intertwined with that amplifier on the aux speaker line. You also state “the external audio jack goes to an amplifier and is then transmitted to the speakers in our firehouse”. I question your use of the word transmitted. Can we substitute “wired” for “transmitted”? Or are you using some type of wireless connection?

Sorry about that yes the amplifier is wired to speakers throughout the fire station. Nothing wireless.

 

[bob550]

You can safely check for voltage using a non-contact voltage tester provided it is designed to detect low voltages.

 

[tvengr]

Does the amplifier have a balanced or unbalanced input?

 

[n1chu]

Correct me if I’m wrong but;
Could it have something to do with what Uniden incorporated into the aux headphone jack to help against damaging eardrums due to high levels of volume. They lowered the max level of volume. When they did this they created a second ground level. So there’s 2 different grounds, one is chassis ground and the other is headphone ground.

I can’t reason how this may be the cause of your issue but maybe others have an answer.

 

[WA0CBW]

At one time I remember a warning about not connecting the external speaker ground to the antenna ground. Is the antenna ground common with the amplifier ground?
Bill

 

[tvengr]

At one time I remember a warning about not connecting the external speaker ground to the antenna ground. Is the antenna ground common with the amplifier ground?
Bill

You need to use a stereo plug on the scanner speaker output. A mono plug shorts out half of the audio output amp. The audio output circuit on the BCD536HP floats. The ground on the speaker output is not connected to the scanner ground. There needs to be an isolation transformer between the scanner and amplifier input. The Uniden BC23A amplified speaker uses a stereo plug and has an isolation transformer inside the speaker. Only the tip and sleeve connections are wired in the cable which feeds the input of the isolation transformer in the speaker. The isolation transformer output feeds the audio amp in the speaker. That prevents grounding of the audio amp output in the scanner. When the antenna cable is connected to the scanner, it is probably grounding the scanner case.

 

[n1chu]

Thanks for the input regarding grounding. It’s that which I hoped would generate thinking towards the OP’s issue.