This discussion is beginning to confuse me. I thought the issue being
debated was the optimal way to provide surge protection to safeguard
our radios from unexpected line transients, and not how to reduce hum
in unbalanced audio circuits caused by ground loops or ground return
currents.
It's actually a related issue, because it is common mode and bad port
design.
I'm perplexed by recent trends to impose unrealistic requirements in
consumer installations to work around poor port designs. Wide ranges of
real-world installations are just not going to be able to have zero
potential between chassis on isolated pieces of gear. Once a cable is out of
a cabinet, the designer has to face the fact he has little control over
common mode and surges. The port should be designed with reasonable
immunity, rather than telling the rest of the outside world they need to be
perfect in every way.
I believe the conventional wisdom is that both whole-house
surge protectors and local surge protectors in combination provide the
most effective safeguard. I'm afraid I don't understand how a surge
protector that clips an, e.g., 1KV spike on a 120 VAC line can end up
doing more damage than no protection all. I understand that the
clipped current pulse returns through the ground line and will cause a
voltage spike on the ground, and I also understand that other
interconnected equipment connected to different grounds may
potentially see part of the spike, but on balance that seems to me to
be a less dire situation than having no protection at all.
I agree with you 100%, Jim. I have MOV protected surge protection outlets at
every computer and entertainment group in my house. I also have outlet
strips like that in my shop and in my house. While I generally do not depend
on MOV's, and do not have lightning arrestors on my feed cables, I do use
outlet strips like that for two reasons:
1.) To protect a device that is particularly sensitive to power line surges
2.) As a common point for RF grounding and bypassing in a hub, usually with
a piece of gear that generates or receives RFI from a poorly filtered power
line connection
I think advising against MOV protected strips because some remote piece of
gear might have a bad port design is not a good first choice.
The trend to correct for bad port designs by demanding the rest of the world
have zero or nearly zero cabinet ground potential differences is
unrealistic, and will only lead to progressively worse port designs as blame
for any damage or operating maladies is shifted to use of reasonable
installations.
There is a radio, for example, that has a ~0.7 volt logic threshold on a QSK
transmit activation line. The manufacturer blames external interfaces and
wiring when the radio malfunctions, but they are the ones who used an
unreasonable 0.7 volt threshold in their design. This blame-shifting trend
by people who do poor port designs is seemingly expanding. This is really
why we are having so many problems with noise or damage on ports.
73 Tom
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Topband Reflector
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