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Author Topic: Why am I supposed to make a second ground connection? Isnt this a ground loop?  (Read 1113 times)

KD6VXI

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  • Posts: 1022

With any modern bipolar transistor output based ham radio you won't get the DC ground buss off the AC safety buss.

The emitter of the transistors is bonded to the heat sink, which in most radios is bonded to or an integral part of, the chassis.

As such, as soon as you hook the radio up, the negative lead of the power supply and whatever 'ground system' you have on the chassis of your radios is now bonded together.

Via the emitter junctions of the output transistors.  What's sad is, most CB radios don't suffer from this as they are designed for positive and negative ground.  If your ham radio doesn't EXPLICITLY state it's for positive ground and negative ground use, you can make a damn safe bet that the chassis is at DC ground potential.

--Shane
WP2ASS / ex KD6VXI
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W9WQA

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note to new guys...
to be continued when i wake up.....
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KC6RWI

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  • Posts: 901

I've been reading and reading, maybe we should start with a battery powered radio in a field with a ground rod and then add a house with an ac service ground.
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W9WQA

  • Member
  • Posts: 990

With any modern bipolar transistor output based ham radio you won't get the DC ground buss off the AC safety buss.

The emitter of the transistors is bonded to the heat sink, which in most radios is bonded to or an integral part of, the chassis.

As such, as soon as you hook the radio up, the negative lead of the power supply and whatever 'ground system' you have on the chassis of your radios is now bonded together.

Via the emitter junctions of the output transistors.  What's sad is, most CB radios don't suffer from this as they are designed for positive and negative ground.  If your ham radio doesn't EXPLICITLY state it's for positive ground and negative ground use, you can make a damn safe bet that the chassis is at DC ground potential.

--Shane
WP2ASS / ex KD6VXI

?,,,cant make sense of this...
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KD6VXI

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  • Posts: 1022

You can't make sense that almost every single amateur radio with a bipolar based power amplifier is going to have the DC ground on the case?

The case is usually attached to the heat sink.  The transistors are attached to the heat sink.  The emitter of the transistor is at dc ground potential and the case of the transistor is usually the emitter on RF bipolars.

Ergo, if the transistor is bolted to metal that is in any way attached electrically to the chassis, nothing you do in your power supply is going to isolate the negative lead of the power supply from the chassis of the radio....  Which in turn attaches it to the ground system in your AC electric.

--Shane
WP2ASS / ex KD6VXI
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W9WQA

  • Member
  • Posts: 990

You can't make sense that almost every single amateur radio with a bipolar based power amplifier is going to have the DC ground on the case?

The case is usually attached to the heat sink.  The transistors are attached to the heat sink.  The emitter of the transistor is at dc ground potential and the case of the transistor is usually the emitter on RF bipolars.

Ergo, if the transistor is bolted to metal that is in any way attached electrically to the chassis, nothing you do in your power supply is going to isolate the negative lead of the power supply from the chassis of the radio....  Which in turn attaches it to the ground system in your AC electric.

--Shane
WP2ASS / ex KD6VXI

and, that works just fine...so?
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