TWL: More on RF Grounding (sorry!)
All:
The following paragraph came from the ICOM manual "Grounding and Antenna
Considerations" (not part of the Gordon West series that Frank pointed
to):
"Poor RF grounding will also lead to erratic movement of analogue dial
instruments, bizarre behavior of automatic pilots while transmitting on
the sideband set, and may even cause burn-outs of tiny integrated
circuits in companion marine electronic gear aboard. ======> Isolating
your RF grounding system from your DC grounding system will prevents
these unwanted occurrences. <======"
Note the last (highlighted) statement. After reading everything I could
turn up, I was coming around to the idea of tying the ground into my
hull (which is in electrical contact with the engine, which is part of
the DC grounding system). Then I ran head-on into this statement.
Does it make sense? Or is it a red herring?
Also, on the RF interference issue, there's lots of talk about
interference from fluorescent lights. My boat has a dozen or so small (8
watt) DC fluorescent lights. Am I going to have to do something special
with these lights?
Thanks,
Keith
Hi Keith,
The statement about isolating your RF grounding system is probably the
writers "CYA" line. There are so many metal components in a boat in such
close proximity to each other that the net effect of keying up your SSB
transmitter will be to RF couple everything in the vicinity, with the
various components appearing at different RF power potentials. Still,
everything will display some measurable potential. Since the wavelength of
an HF frequency wave is so long, you can't totally isolate the 2 grounding
systems. From my perspective (and some will argue this point), the
difference of potential issue and its concurrent risk to personnel is far
more serious than the likely RF interference that may arise from not
isolating the 2 grounding systems.
My strategy would be to bond the 2 systems and, if there were RFI problems,
attempt breaking the bond as a last resort solution. I realize that on your
boat isolation is at least problematic and maybe impossible. I also turned
up information on metal hull vessel SSB installations where the hull
provided the ground plane. None referred to any problems as described in
you quotation.
The noise from fluorescent lamps usually comes from the ballast /
transformer section. At 8W each there should be little or no issue on your
boat. Regardless of my opinion, nothing beats actually testing the
configuration and seeing how things interact. Every installation is unique
and although it will greatly benefit from prior planning, it will usually
display some quirks of its own that challenge your ingenuity.
Best Regards,
Frank & Claudette Weismantel
Elverta, CA
Boatless for a little while longer
-----Original Message-----
From: trawler-world-list-admin@lists.samurai.com
[mailto:trawler-world-list-admin@lists.samurai.com]On Behalf Of Keith Pleas
Sent: Monday, July 15, 2002 8:51 AM
To: 'Trawler-World-List'
Subject: TWL: More on RF Grounding (sorry!)
Keith wrote:
After reading everything I could
turn up, I was coming around to the idea of tying the ground into my
hull (which is in electrical contact with the engine, which is part of
the DC grounding system). Then I ran head-on into this statement.
Does it make sense? Or is it a red herring?
REPLY
In nearly every textbook you find dealing with grounding in one form or
another, each type of ground is dealt with in isolation. ( pardon the pun)
Lightning grounds should run in vertical directions only and should avoid
horizontal wiring runs.
Bonding for galvanic corrosion protection should run horizontally and use
coarse stranded wire. They specifically warn against using fine stranding or
mesh type ground straps such as you see in automotive use.
Several Standards ( not ABYC) require a #8 ga wire
One called for #12 but ABYC requires #4 and it must be fine stranded.
AC grounding connects only to the metallic enclosures of the AC electrical
system and should use #14 ga wire.
DC grounding articles usually suggest simply bolting to the engine block and
doesn't always specify wire size. However, they warn against wiring in the
bilge area and recommend running the wiring high up and dropping a wire
down to the low connection points. This now calls for a combination of vertical
and horizontal wiring runs. Which is contrary to the lightning grounding
recommendations.
RF grounding often talks about flat copper foil and horizontal mesh ( fine?)
but does not recommend normal insulated wire.
And of course the communications people have their own requirements which
totally ignore the other standards.
All in all, its very confusing!
While preparing a text book on the subject of marine wiring practices, I asked
an electrical engineer on my committee to consult with CSA, the Canadian
Standards Association, for a clarification on how to interpret the various
standards they had for grounding.
CSA has published a standard for each type of grounding. DC, AC, Lightning
and Bonding.
Despite trying for more than two years, we could not get a straight answer out
of them. CSA and UL normally have reciprocal certification and approval
arrangements. No luck with UL either.
Its no wonder than that this discussion thread brings out a lot of apparently
conflicting information.
My suggestion is to wire up each grounding/bonding system as a separate
entity following the recommended practice set forth for each in the standards.
Then designate one bolt or busbar as the COMMON single point of
connection between all the various ground systems. Run suitable conductors
from this one point to each of the separate systems.
If you then discover an apparent grounding issue, at least now you have a
common reference point. You can disconnect each system in turn to see
what effect this has on your problem.
This type of connection is called a radial or star ground.
There are no daisy chain loops going from one piece of equipment to another.
Good luck
Arild
One of the better works on this subject is Stan Honey's article in PS which
can be found, care of West Marine, at:
http://www.westmarine.com/webapp/commerce/command/ExecMacro/west_advisor.d2w
/show_advisor?fn=50.htm&store_num=9
Note thagt this is an attempt at a holistic solution to all the ground
problems at once.
On the general subject of dealing with rf interference the Jim C article is
at:
http://members.aol.com/CruisingServices/pdf/RFI.pdf
Jim
For what it is worth, I would try capacitive coupling the ground to your
engine / shaft / prop and see how well the antenna tuner likes it on various
frequency ranges. The capacitor may be able to be left out for a test if
there is no great voltage potential present between the radio ground and the
engine.
You may find that there is enough "ground" in your engine / shaft and prop
to do you quite well. By using a capacitor in series with the ground you
will avoid any "ground loops" and the associated electrolysis.
I believe that you are in the Seattle area so trot on over to Amateur Radio
Supply (I think they are still in business over near the Space Needle) and
get a ceramic capacitor with a value somewhere around 0.01 microfarads and
just connect it between the end your ground lead and a bolt that is easy to
get at on the engine.
If you do not have sufficient copper strap for the test, copper plumbers
strap is cheap and will work quite well. If its more convenient, open up the
engine hatch and run the temporary ground thru the hatch, its only a test at
this point.
I have a very strong suspicion that your vessel has enough grounded goodies
that your radio will work very well with this set up and you will save
yourself a lot of money and work plus you get the ground down to the water
where it belongs.
For your info, and I am not trying to scare you, on my boat there were more
things that interfered with the SSB than not. It took about a year of
cruising and tinkering before I found a cure for them all but in the end I
did. Most of the interference was cured by bypass capacitors and car stereo
"noise filters" that I got cheaper from Radio Shack than I could build them
myself. The last long cruise we took I ran the SSB almost continuously for
the month we were out except for the brief periods we were in a "Town" where
the interference was so bad I had to shut it down. I was operating in the 7
MHz band and in remote areas I could turn the gain up full and still not
hear any electrical noise from the boat while under way. God bless a diesel
engine !!
Hope this helps you get around your problem.
Good Luck
John Tones MV Penta
Victoria, BC
See...just keep asking until you get an answer you like. <g>
For what it is worth, I would try capacitive coupling the ground to
your
engine / shaft / prop and see how well the antenna tuner likes it on
various
frequency ranges. The capacitor may be able to be left out for a test if
there is no great voltage potential present between the radio ground and
the
engine.
It seems like it would be hard to test for that potential when
transmitting.
You may find that there is enough "ground" in your engine / shaft and
prop
to do you quite well. By using a capacitor in series with the ground you
will avoid any "ground loops" and the associated electrolysis.
Stan Honey's article in PS (which Jim pointed out today) mentions this,
and it's starting to sound like the right approach. All the people who
just said "wire everything together, no problems" were kinda scaring me.
<g>
I believe that you are in the Seattle area so trot on over to Amateur
Radio Supply (I think they are still in business over near the Space
Needle) and get a ceramic capacitor with a value somewhere around 0.01
microfarads and just connect it between the end your ground lead and a
bolt that is easy to get at on the engine.
Well...Stan Honey's article recommends using several .15uF ceramic
capacitors with a custom isolator setup (in what must be a typo, though,
the illustration says "10.15uf"). So, what's the right specification? Or
does it not really matter?
If you do not have sufficient copper strap for the test, copper
plumbers
strap is cheap and will work quite well.
You must have missed the post where I mentioned I bought 120 square feet
(60' by 2') of 5 mil and 14' x 6" 21 mil. No, I don't think I'm going to
be short on copper material. <g>
I have a very strong suspicion that your vessel has enough grounded
goodies that your radio will work very well with this set up and you
will save yourself a lot of money and work plus you get the ground down
to the water where it belongs.
Now that this capacitor-based insulator thing has cropped up, I'm
getting over my fear of connecting it to my hull armature (I have a 44'
ferro-cement trawler that displaces 38 tons, so I think there's a fair
amount of metal in there).
Most of the interference was cured by bypass capacitors and car
stereo
"noise filters" that I got cheaper from Radio Shack than I could build
them
myself.
Thanks for the tip!
Thanks,
Keith