>> This is good advice ... and always bond the chassis of each piece
>> of equipment to the common ground point and not "chassis to chassis."
>
> This is the only advice that I disagree with. Low impedance bonding
> chassis to chassis of equipment that mave an unbalanced signal
> connection between them is a VERY GOOD THING, because it can
> effectively short out any voltage that may be present between them
> (like the IR drop being discussed here).
Bonding unit to unit ENCOURAGES common mode currents to flow through
all of the units in series. Bonding to a single LOW IMPEDANCE ground
moves the common mode and RF currents to the ground and *NOT* the
other equipment.
The purpose of grounding/bonding is to eliminate common mode currents
and tie everything to a common reference. "Daisy chain" bonding,
particularly when done with a few small gauge wires can encourage
common mode problems - particularly where there are issues in the
transceiver V- connection.
73,
... Joe, W4TV
On 9/12/2010 12:34 PM, Jim Brown wrote:
> On Sat, 11 Sep 2010 20:06:50 -0400, Joe Subich, W4TV wrote:
>
>> This is good advice ... and always bond the chassis of each piece
>> of equipment to the common ground point and not "chassis to chassis."
>
> This is the only advice that I disagree with. Low impedance bonding
> chassis to chassis of equipment that mave an unbalanced signal
> connection between them is a VERY GOOD THING, because it can
> effectively short out any voltage that may be present between them
> (like the IR drop being discussed here).
>
> Don said:
>
>> Strange modulation of the V- line to the accessory can result,
>> especially with SSB transmission,
>
> Nothing strange about it, it's simple Ohm's Law. :) You have DC
> current on the V- lead that reaches a peak value of at least 20A, so
> there is voltage drop on that lead as predicted by Ohm's Law. That
> voltage drop becomes a problem if it appears between equipment that
> has unbalanced connections, like a computer sound card and a rig, or
> between an outboard audio interface and a rig. That's why an interface
> device SHOULD be powered from the end of the power cable nearest to
> the rig, which is the basis of Joe's advice.
>
> W8JI was the first guy I know of who brought this problem to our
> attention. That IR drop from current that varies with SSB modulation
> from about 1A to about 20A will sound very much SSB audio in an AM
> detector, and just like RF in the audio. So you THINK you have RFI,
> but what you really have is simple IR drop. That's why I've asked
> about power and bonding in this discussion.
>
> Another part of this equation is whether V- is bonded to the chassis
> in the power supply. In general, it should NOT be bonded. Most power
> supplies are built so that they are either NOT bonded, or have a
> single bond that can easily and safely be removed. The linear Astrons
> are an example -- the entire V- bus floats all the way through the
> supply, but is bonded near the V- terminal. This can very easily and
> safely be cut.
>
> Now, getting back to Felipe's RFI problem. If, as I suspect, it's a
> pin 1 problem in the computer sound card, the ferrite choke could fix
> that problem. But if it's the DC power problem, removing the V- bond
> in the Alinco power supply (if there is one) would be a likely
> solution. I think the DC power problem is unlikely in this situation,
> because, as I understand it, it's the FT2000 RF that is getting into
> the K3 audio, and it's running on it's own internal supply.
>
> 73, Jim K9YC
>
>
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