"Doug Dotson" dougdotson@NOSPAMcablespeedNOSPAMcom wrote in
:

Have you priced a crimping machine that is capable of dealing with most
reasonable moisture proof connectors?

Doug



There aren't any "moisture proof connectors" on any NMEA crap I ever
had....just wires hanging out of a box or screw terminals on a box....

"engsol" wrote in message
...

As to 4800 baud radiating for 1 inch unshielded...not much chance of that.
The only exception might be if the rise time of the pulses was quick
enough...often seen in switching power supplies....to cause the old
'comb' of harmonics.

Indeed, that's why any decently designed device should have some form of
limit to the risetime, which is not hard at all. We simply put an RC network
on each dataline. But also having galvanically isolated inputs, which is
dictated by the NMEA standard, will ensure a proper balance in both wires of
an NMEA connection, ensuring minimal radiation. The problem is however, that
many manufacturers try to cut corners here.

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 @

Bruce in Alaska wrote in news:bruceg-
:

Ground is not Ground, the world around....RF Grounds are different
than other Grounds, and should not be confused with these other
Grounds.



1/4 wavelength down the wire from "ground", a voltage reference to which
other points are measured, is an OPEN. At this point, induced voltage in
the "ground wire" or "shield" is at maximum, and can be high enough to kill
around high powered transmitters. As you approach 1/2 wavelength from
"ground", once again you find a null of voltage. Again at 3/4 wavelength
from "ground", we once again find a maximum voltage lobe that may burn you.

We don't HAVE to connect anything in RF to "ground ground", Mother Earth,
to get a "ground". If we lay out a piece of wire and keep the end from
touching anything conductive, usually by putting an insulator there or
using tubing at higher frequencies which requires no insulator and support
structures to hold it up...we get an "artificial ground". Look at any
common CB "ground plane" antenna and note the "radials" sticking out from
the base where the coaxial shield is connected to these "radials" that are
1/4 wavelength long. The end of the radials is open, at least a very high
impedance in common air. 1/4 wavelength back from that "open" is the
artificial ground, where the coax shield is connected. This point performs
at some high altitude just as if the shield were connected to "ground
ground", as far as the RF is concerned (but NOT the lightning!). A 1/4
wavelength "sleeve" (beer cans with the ends cut out welded together end to
end work great for hams), with the coax going up inside the sleeve but not
touching its open end, also makes an artificial ground 1/4 wavelength away
from the open end.

--
Larry

This jerk called my cellphone and was nasty.
Continental Warranty -- MCG Enterprises -- Mepco-
24955 Pacific Coast HWY Suite C303
Malibu California 90265
888-244-0925
Fax: 310-456-8844
Email:
Read about them he
http://www.ripoffreport.com/view.asp...3&view=printer

"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

I guess that explains how Aircraft are able to transmit and receive, too.

Thanks Larry, Meindert, and Bruce for your comments.

Dave.


"Larry" wrote in message
...
Bruce in Alaska wrote in news:bruceg-
:

Ground is not Ground, the world around....RF Grounds are different
than other Grounds, and should not be confused with these other
Grounds.



1/4 wavelength down the wire from "ground", a voltage reference to which
other points are measured, is an OPEN. At this point, induced voltage in
the "ground wire" or "shield" is at maximum, and can be high enough to
kill
around high powered transmitters. As you approach 1/2 wavelength from
"ground", once again you find a null of voltage. Again at 3/4 wavelength
from "ground", we once again find a maximum voltage lobe that may burn
you.

We don't HAVE to connect anything in RF to "ground ground", Mother Earth,
to get a "ground". If we lay out a piece of wire and keep the end from
touching anything conductive, usually by putting an insulator there or
using tubing at higher frequencies which requires no insulator and support
structures to hold it up...we get an "artificial ground". Look at any
common CB "ground plane" antenna and note the "radials" sticking out from
the base where the coaxial shield is connected to these "radials" that are
1/4 wavelength long. The end of the radials is open, at least a very high
impedance in common air. 1/4 wavelength back from that "open" is the
artificial ground, where the coax shield is connected. This point
performs
at some high altitude just as if the shield were connected to "ground
ground", as far as the RF is concerned (but NOT the lightning!). A 1/4
wavelength "sleeve" (beer cans with the ends cut out welded together end
to
end work great for hams), with the coax going up inside the sleeve but not
touching its open end, also makes an artificial ground 1/4 wavelength away
from the open end.

--
Larry

This jerk called my cellphone and was nasty.
Continental Warranty -- MCG Enterprises -- Mepco-
24955 Pacific Coast HWY Suite C303
Malibu California 90265
888-244-0925
Fax: 310-456-8844
Email:
Read about them he
http://www.ripoffreport.com/view.asp...3&view=printer