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Splicing shielded wires on Icom VHF

Old 06-03-2016, 03:43 PM
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Default Splicing shielded wires on Icom VHF

I am installing an Icom M412 VHF radio. The single external speaker and two NMEA 0183 wires are shielded. The shielding is the negative side of the path, so there are 6 conductors in three wires.

How do I go about splicing or putting connectors on these wires? I need to connect some wire to the external speaker output, and probably ring or fork terminals to the NMEA output/input.

Here are some links to help clarify:

http://www.thehulltruth.com/marine-e...uestion.html#b

http://www.icomamerica.com/en/downlo...x?Document=528

Thanks!
Old 06-04-2016, 05:32 AM
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Splicing is easy, just peel back the shielding and twist the mesh into a single wire. I usually cut the shield back so it is an inch or so shorter than the center conductor. Now just attach solder and shrink tube the two connections to the shield and center conductor.


It is a good idea to add a third piece of shrink tube over the two connections and back past where you peeled back the shield to protect and seal the entire splice.


You can also use a terminal strip or NMEA connection block to make the splice connection.


Jim
Old 06-04-2016, 05:36 PM
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First of all, you do not need to connect any of those NMEA-0183 shields. They are just chassis or ground potential. They are not active signals. In NMEA-0183 interfacing you do not need the shield to carry across the interconnection to the other device. For more advice on how to make a proper NMEA-0183 interface, see

http://continuouswave.com/forum/viewtopic.php?f=9&t=816

As for how to make a shield into a conductor, here is the method I have used for the past 50-years to do this thousands of times:

If the shield conductor has a braided weave, the best way to turn it into a separate conductor is to un-weave the braid so it turns into individual fine conductors. Then twist those individual fine conductors into a single twisted conductor. I use a small pic tool to help un-braid the braided shield. Fan out the individual conductors as you unbraid the shield. When you have un-braided the shield back to the start of the cable's insulation, then twist it into a new single conductor. Tin the loose end so the conductor stays twisted together. Cover the bare conductor with some insulating sleeve. You can use heat-shrink tubing. You can also cover the area at the end of the insulation to the rest of the conductors with some larger heat shrink.
Old 06-04-2016, 06:10 PM
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Originally Posted by jhebert View Post
First of all, you do not need to connect any of those NMEA-0183 shields. They are just chassis or ground potential. They are not active signals. In NMEA-0183 interfacing you do not need the shield to carry across the interconnection to the other device. For more advice on how to make a proper NMEA-0183 interface, see

http://continuouswave.com/forum/viewtopic.php?f=9&t=816

As for how to make a shield into a conductor, here is the method I have used for the past 50-years to do this thousands of times:

If the shield conductor has a braided weave, the best way to turn it into a separate conductor is to un-weave the braid so it turns into individual fine conductors. Then twist those individual fine conductors into a single twisted conductor. I use a small pic tool to help un-braid the braided shield. Fan out the individual conductors as you unbraid the shield. When you have un-braided the shield back to the start of the cable's insulation, then twist it into a new single conductor. Tin the loose end so the conductor stays twisted together. Cover the bare conductor with some insulating sleeve. You can use heat-shrink tubing. You can also cover the area at the end of the insulation to the rest of the conductors with some larger heat shrink.
Interesting. This is what the link says regarding these Icom units:
(On these devices, the cable may include a shield conductor. It is not clear
if the shield is just a chassis ground or an active B signal.)
TALKER A = White
TALKER B = not provided
LISTENER B = not provided
LISTENER A = Red
So, are you saying that I can just leave the shielding completely disconnected? What about the negative or B wires on the GPS? Do they just get connected to ground?

Regardless, I do need to use the shield portion of the external speaker wire. I don't believe it's braided, but otherwise I think I will do essentially what you guys are suggesting and layer a couple tubes of heat shrink to insulate and seal the wire.
Old 06-04-2016, 06:23 PM
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Here you go

Old 06-04-2016, 06:24 PM
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Originally Posted by K-dawg View Post

So, are you saying that I can just leave the shielding completely disconnected? What about the negative or B wires on the GPS? Do they just get connected to ground?

Regardless, I do need to use the shield portion of the external speaker wire. I don't believe it's braided, but otherwise I think I will do essentially what you guys are suggesting and layer a couple tubes of heat shrink to insulate and seal the wire.
The shield should just be the chassis which should just be the battery negative. In the recommended practice of NMEA-0183 it is not carried across the interface.

You can use the shield as the ground conductor at the interface if you like and if it makes it easier. I would just bring a battery negative conductor to the interface.



Re the ICOM signals, it is not very clear from ICOM if the shield conductor has an active signals or it's just a shield. Most likely they're just a shield and the NMEA signals are just a TALKER A and LISTENER A. The manual is quite mum about this. This radio is an older generation. ICOM's newer radios are much better at compliance with the standard.

For the speaker, my remarks about the NMEA interface do not apply. The speaker circuit is not part of the NMEA circuit.

Shield conductors that are not braided are much easier to handle, but they are probably not very effective shields compared to braided shields.

Last edited by jhebert; 06-04-2016 at 06:34 PM.
Old 06-07-2016, 12:07 PM
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OK, I was mistakenly thinking that I would use four NMEA wires on the Garmin 7612, but it looks like I will use only two - Port 1, Blue and Brown.

And it sounds like the VHF's Red (in) shield should be connected to a ground, and the White shield can be disregarded. Is this correct? JHebert, why do you say that I should have a ground conductor at the "interface"? I was going to use a small terminal strip to connect the wires.

I can make anything that's already complicated, even more complicated. Thanks, for the help, guys.
Old 06-08-2016, 01:07 PM
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Originally Posted by K-dawg View Post
OK, I was mistakenly thinking that I would use four NMEA wires on the Garmin 7612, but it looks like I will use only two - Port 1, Blue and Brown.

And it sounds like the VHF's Red (in) shield should be connected to a ground, and the White shield can be disregarded. Is this correct? JHebert, why do you say that I should have a ground conductor at the "interface"? I was going to use a small terminal strip to connect the wires.

I can make anything that's already complicated, even more complicated. Thanks, for the help, guys.
To answer my own question, the radio's Red (In, Listener, Rx, whatever) shield needs to be connected to ground. The radio's White (Out, Talker, Tx, whatever) shield is not connected to anything. The Red wire itself gets connected to the Garmin's Blue (Out, Talker, Tx), and the radio's White gets connected to the Garmin's Brown (In, Listener, Rx).

I tried it without connecting the Red shield to ground and it didn't transfer the position data. I had to hook up the ground to get it to work.

I ended up skipping the terminal strip and soldering the wires for the NMEA and external speaker.

Thanks again for the assistance, jhebert.
Old 06-08-2016, 03:02 PM
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Many manufacturers use the the shield as the RX and TX negatives. The reason is to pull down the data levels to zero volt reference for both, as the data actually operates LED which are optically detected by a phototransistor in the equipments. Besides, it will either work or won't work
Old 06-08-2016, 07:40 PM
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Did not know optics were involved. Cool!
Old 06-09-2016, 06:38 AM
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Originally Posted by K-dawg View Post
Did not know optics were involved. Cool!
This is standard RS232 opto coupler as used for NMEA0183.
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