[C38] SSB Radio Grounding

[Les]

Hi, everyone,
	I just realized that I wasn't clear on this grounding issue.  
DC return is not RF ground.  DC return is the (usually black wire) DC
connection carrying the 
amps required by the radio.  This has to return to the engine.  On the
transciever, there should 
(on all radios for marine use I have seen anyway) be  a ground stud with
nut 
and lock washer.  This is usually labeled RF ground.  But occasionally
there is no label.
This stud is for the ground counterpoise.  If you ask 10 engineers or 10
amatuers you will
most likely get 20 good answers to how to manage this ground.  However,
be aware that RF
doesn't flow like DC.  As it goes around corners, or through wires, it
builds up fields.  
These fields like to increase the effective impedance (think of it as AC
resistance, but 
affecting only current or only voltage).  As this occurs spikes in
current or voltage will
be created.  If there is no low impedance path to prevent high build up,
these "loops" of 
voltage or current can be quite high.  This is what can harm your diodes
in your engine's alternator.

If a good low impedance path to earth is provided, earth will absorb the
power from the reflected energy
and prevent the loops from getting too high (at least that is a
convenient way to think of it).

So the right or at least the best solution is a separate very low
impedance to earth for the RF ground.
That means using either some ground plate on the outside of the hull, or
a large area of metal inside
the hull below the water line to act like a capacitor to pass the RF
signal to earth ground through 
the hull.  Whatever the choice, it should have a copper ribbon of
sufficient width (about 1 or 2") to spread the field as it runs to this
very low impedance ground.  Be sure that this ground also goes to the
tuner for the antenna.  

	I am not saying this is the only way, just that this is the safest and
most efficient use
of the RF signal and to prevent damage to the boats other electrical
systems from stray RF, along with reduced RF burn or shock hazard to you
when you work on other systems (preferred is to shut down the SSB any
time you are doing 
electrical work on a small vessel.)


	DC return, that BIG BLACK wire carrying 10-15Amps for a 100 watt radio,
should go directly to the engine block, and should be sized for 25 Amps
using standard wire size for the length of the run.  Most systems I have
seen use #8 or #10 wire for up to 25 feet for both red and black (+12
and return).  Gordon West has some good information in his book.

Regards,
Les H

On Tue, 2008-03-11 at 22:49 -0700, Les wrote:
> The counterpoise also carries RF, until it reaches the ocean.  The
> wavefront builds according to the physical configuration of the mass
> tied to the element (in this case the coaxial sheild), if this is the
> only path to ground.  In the case of an engine block and associated
> wiring, the RF will or at least can setup a field that puts a voltage
> node at the alternator.  This voltage is in essence unconstrained,
> consisting of the voltage loops of SWR.  The diodes of an alternator can
> handle a lot of current, but their voltage limitatioin is typically 35
> or so volts.  The RF loops on 50 ohm conductor are up to 70v at 100w
> (the typical power out of a marine HF transmitter).  The possibility
> exists that on some frequency the voltage peak could manifest at the
> alternator and poof, there go the diodes.  ANd being a boat, Murphy
> applies, only in a storm, with other problems as well, then you can kiss
> your anode good-bye ;-)
> 
> Regards,
> Les H
> 
> Regards,
> Les H
> On Tue, 2008-03-11 at 22:07 -0400, Tom T. wrote:
> > Les,
> > 
> > How will "stray" RF burn out the diodes if the RF counterpoise is grounded
> > to the block and not to the DC positive side of the alternator?
> > 
> > Tom Troncalli
> > 
> > 
> > 
> > 
> > > [Original Message]
> > > From: Les <hlhowell at pacbell.net>
> > > To: <larrypi at linkline.com>; Catalina 38 Listserve
> > <listserve at catalina38.org>
> > > Date: 3/11/2008 6:20:31 PM
> > > Subject: Re: [C38] SSB Radio Grounding
> > >
> > > HI, everyone,
> > > 	Do NOT do this.  You run the risk of blowind your alternator diodes
> > > with stray RF.  The specs call for a separate RF ground for good reason.
> > > The engine to ocean ground is via the propshaft, and that doesn't have
> > > sufficient planar area either.  Get the 
> > >
> > > Boatowner's Guide to Marine Electronics  by Gordon West.  You can get a
> > > used copy for 6.99 from Amazon.  Read it.  Follow its instructions.
> > >
> > > 	If you are not a radio amatuer, get the radio professionally installed.
> > > It will save you lots of headaches and be more reliable.  If you are a
> > > radio amatuer moving to marine means just learning what does and doesn't
> > > work.  One thing for sure, get the self sealing tape for connectors
> > > (similar to rigging tape).  Use it on all connectors.  The best process
> > > is to properly assemble the connector, apply some marine silicon sealant
> > > to the fixed part of the shell, then cover that with the self sealing
> > > tape.  After the connectors are joined outside, cover the whole
> > > connection, starting about 1" back on the cable to as good as you can
> > > get beyond the other connector.  This keeps out salt, water, corrosion
> > > and curious birds, all of which can defeat your radio's connections.
> > > (Old ETC talking here with 20 Navy years behind him.)
> > >
> > > Regards,
> > > Les H
> > > On Tue, 2008-03-11 at 10:54 -0700, Larry Malmberg wrote:
> > > > Has anyone grounded their SSB to the engine?  If so, how has it worked
> > out?
> > > >