[Elecraft] [K3] Serial interface noise issues

[Rick Bates]

Thank you Don, that was clear and concise.  

I'm not an expert on radios or RF like some on this list.  I just try to go
with what works.  I was a firefighter in my previous life.  We adapt and
overcome.  I make things work, then I make them 'pretty'.  (Pretty in this
case means safer, more reliable and sometimes putting a 'bow on it.)  Simple
is good; it's often easier and elegant too.

We're basically saying the same thing but coming in from different points.
Chassis to chassis bonding is wanted, whenever possible.  It's not always
possible.  My old shack laptop has a two wire (ungrounded) mid line wart
power connection and bonding the laptop chassis to the station is an
exercise in futility (no grounding point on the laptop; the third wire if
any, grounds the power supply not the laptop).  A desktop chassis should be
bonded to the station (yes, as required by code but one size doesn't always
fit).

And yes, audio 'ground' (return) is rarely chassis ground these days.  We
agree again though I may have phrased it poorly or used the wrong terms
(floating ground) or examples, it was something I was trying to point out.
But that is a very common mistake to make too.  The two 'grounds' aren't the
same and connecting one to the other can cause huge problems, balanced or
not.  Don't assume that audio ground is chassis ground, it's not that way
anymore.

Considering the floating pin one problem, that makes many 'ground' wires,
(audio return, power, chassis and 'pin 1') each with a different meaning.
It'd be easy to presume they're all the same, but they aren't.  It makes
noise reduction even more difficult.

To the original problem of serial data noise:  With so much electronics
generated RF crud floating around a shack from numerous sources, it's often
difficult to find the cause(s) or cure(s) for that noise.  Better cables,
ferrites, common bonding and similar help but it's a long process to have a
quiet shack.  A product may meet FCC spec, but be ham lousy with noise.

What is working for noise reduction for me (K3, bonded to P3 bonded to
KPA500) was moving the antenna farther from the shack and using common mode
chokes to keep as much crud off of the feed as I could (reduced by more than
75%).  Next was finding quieter laptop power supplies or running off of
batteries.  I'm still chipping away at the rest (mostly Ethernet CAT 5 wires
radiating, switching to WiFi).  It has limited success with noise sources
not on my property, but its better. 

And lastly, (then I'll go back to lurking since I'm no expert) when bonding
a station to ground (or at least to each other per NEC for those of us in
upper stories, not close to dirt or plumbing in the shack), while solid wire
meets the NEC code, we're also talking about RF.  So braid is best, followed
by multi-strand wire, and if nothing else at least a solid #10 wire.  Guess
what; if you bond for high RF environments, it works to help keep RF in its
place and meets the code too (you've exceeded the code with wide braid).

Hopefully I was more clear this time.  I get the code, concepts and means
though I may not state it clearly.  Comments, if any, can be made off group,
I'm sure the others are tired of this thread.

73,
Rick WA6NHC

-----Original Message-----
From: Don Wilhelm

I will only comment on the part reproduced below - audio return is NOT 
audio ground.  In the case of the  Motorola amp cited, I suspect the 
audio amp output is a bridged amplifier, and for those, neither speaker 
lead should be grounded (it shorts half of the audio amplifier.

BUT, Jim Brown was talking about unbalanced audio inputs, not speaker 
outputs.  In the ham world and the world of consumer audio, most audio 
inputs are unbalanced, with one conductor (the shield) connected to 
"ground".  That ground used to be the equipment enclosure, but more 
recent implementations circumvent that and put the connection to the 
shield onto the PC board rather than the enclosure - and often the 
enclosure is plastic which creates yet another set of potential problems.

We used to connect our audio (and RF) jacks directly to the enclosure 
and then inside the enclosure, we would route that connection to the 
circuit contained in that enclosure - no "pin 1" problems because the 
shield of connected cables were connected first to the outside of the 
enclosure..  In today's implementations, pin 1 problems abound because 
jacks for any and every purpose are designed to connect to the PC board 
and may or may not have any connection to the equipment enclosure.
That allows noise and other undesired signals to be introduced onto the 
device circuit board without being first stripped off by the (grounded) 
metallic enclosure for the device in question.   We have come a long way 
in convenience for manufacturers, but several problems have occurred 
along the way, and they are not easy to correct.

73,
Don W3FPR