Meindert,
The problem is that all the Raymarine Seatalk cables use red for yellow
for data, red for + volts, and the shield for - volts. Saves cost of s
third wire.
krj

Meindert Sprang wrote:

"krj" wrote in message
. ..

Larry,
Do you have ferite beads at both ends of all your NMEA cables? If so, do
they help?


Ferrite beads don't do much on HF, but all the more on VHF. But like I said
in me other replay, it's more important to terminate the wire correctly. If
you have a shield, do not use it as a signal return as with coaxial cable.
Only connect it on one side so no current can flow through the shield,
otherwise it will radiate being a perfect antenna.

Meindert

krj wrote in
:

Larry,
Do you have ferite beads at both ends of all your NMEA cables? If so, do
they help?
krj



I tried that, too. They reduce the noise, somewhat, but the open screw
terminals on the Noland multiplexer, the unbalanced lines making all the
unshielded NMEA cables into a giant transmitting antenna just bypass them
beads or clamshell ferrites so much it's nearly useless.....

I bought a new Maxtor 300 GB external portable hard drive for my system,
today, in a moment of weakness at Best Buy ($299). It came with the nicest
WELL SHIELDED USB-2 and Firewire cables with clear plastic coverings so you
can see the braided shield inside....oh, the longing for a whole boat
network like that...(c;

"Larry W4CSC" wrote in message
...
I'd rather see shielded connectors so I can run shielded pair cables and
RF
bypassing of all inputs to keep the HF SSB from screwing all the NMEA crap
attached to it. Shielding everything would also make it so we could HEAR
the HF receiver and get our WEFAXes without the constant drone of NMEA
radiated interference from all the unshielded, unbalanced connections with
just open wires sticking out of things. NMEA needs to get its act
together
and enforce some standards on its members....

Funny thing is: you don't need shielded connectors to be HF-quiet. The
physical size of two screw terminals and an inch of bare wire ends are
simply not enough to be able to radiate sufficient RF. What does radiate on
HF are long cable runs that are either unshielded or unbalanced. Raymarine
have put our multiplexers to the test to comply with IEC945 for instance,
which limits for susceptibility and emission are rougly ten times more
stringent than FCC Part 15 class B. And it passed that test while being in a
plastic box and having screw-terminals. The really important thing is to
have it wired correctly and, most important, not to connect a shield *at
both ends*.

Meindert

Meindert --

I generally agree with your statement regarding shields.

The question I have, though, is as follows

Given that the ground for an SSB antenna carries a lot of RF current, and
given that all grounds end up tied together at some point aboard a vessel,
by leaving the shields ungrounded at one end, isn't there a risk of creating
a parasitic antenna out of your signal shields.

I have heard reports (not my experience) of the AC safety grounds being
capacitively tied back to ground at their other end to avoid this problem.

I would think this would only be a problem where the cable approximated a
quarter wavelength - which might explain why I have only heard this problem
reported on AC grounds, which could grow to be pretty long.

Has anyone else in the group experienced such a problem, and if so, what did
they do to correct it?

Dave Morschhauser


"Meindert Sprang" wrote in message
...
"Larry W4CSC" wrote in message
...
I'd rather see shielded connectors so I can run shielded pair cables and
RF
bypassing of all inputs to keep the HF SSB from screwing all the NMEA
crap
attached to it. Shielding everything would also make it so we could
HEAR
the HF receiver and get our WEFAXes without the constant drone of NMEA
radiated interference from all the unshielded, unbalanced connections
with
just open wires sticking out of things. NMEA needs to get its act
together
and enforce some standards on its members....

Funny thing is: you don't need shielded connectors to be HF-quiet. The
physical size of two screw terminals and an inch of bare wire ends are
simply not enough to be able to radiate sufficient RF. What does radiate
on
HF are long cable runs that are either unshielded or unbalanced. Raymarine
have put our multiplexers to the test to comply with IEC945 for instance,
which limits for susceptibility and emission are rougly ten times more
stringent than FCC Part 15 class B. And it passed that test while being in
a
plastic box and having screw-terminals. The really important thing is to
have it wired correctly and, most important, not to connect a shield *at
both ends*.

Meindert

In article ,
"Dave M" wrote:

Meindert --

I generally agree with your statement regarding shields.

The question I have, though, is as follows

Given that the ground for an SSB antenna carries a lot of RF current, and
given that all grounds end up tied together at some point aboard a vessel,
by leaving the shields ungrounded at one end, isn't there a risk of creating
a parasitic antenna out of your signal shields.

I have heard reports (not my experience) of the AC safety grounds being
capacitively tied back to ground at their other end to avoid this problem.

I would think this would only be a problem where the cable approximated a
quarter wavelength - which might explain why I have only heard this problem
reported on AC grounds, which could grow to be pretty long.

Has anyone else in the group experienced such a problem, and if so, what did
they do to correct it?

Dave Morschhauser

RF Grounds should NEVER be used as DC Grounds.
RF Grounds should ALWAYS be as short as possible.
RF Grounds are not all created equal, and never will be as good
as you want, or think they should be.
Ground is not Ground, the world around....RF Grounds are different
than other Grounds, and should not be confused with these other
Grounds.


Bruce in alaska more explainations, require more serious study....
--
add a 2 before @

"Dave M" wrote in message
news
Meindert --

I generally agree with your statement regarding shields.

The question I have, though, is as follows

Given that the ground for an SSB antenna carries a lot of RF current, and
given that all grounds end up tied together at some point aboard a vessel,
by leaving the shields ungrounded at one end, isn't there a risk of
creating
a parasitic antenna out of your signal shields.

As long as the indiviual runs of cable are shorter than 1/10 wavelength,
they don't have any influence.
You can break longer runs from an RF point of view by placing toroid cores
every 1/10 wavelength and turn the cable a few times through these toroids.
In such a case, grounding the shield at both ends is better, but should be
done through a capacitor, to prevent any DC of low frequency currents from
floating through the shield. The basic idea is that you prevent any current
from flowing through the shield.

Meindert