Coax cable for long run up mast

[Ericson38]

Originally Posted by Dockhead

The power function directly translates. He's right. And that's why we use dB for both.



20% is very unlikely to make the difference you say. 300% or 400% -- maybe.

Thanks for pointing out my error on low power (1 watt not 5 watts).

The confusion here arises from the fact that the ear is a 10[common]Log proportional hearing transducer. So something that sounds twice as loud as something else (2x) to the listener had to actually be (instrumentally measured) 10dB or (10x) more intense.

So with 10dB giving an impression of a 2x change (up or down) in level, a 1.5dB sound pressure level difference isn't going to be noticeable.

[Dockhead]

Originally Posted by Ericson38

Steve,

Great website. Also, what do you think of the current crop of internal or external AIS splitters ? The external ones I looked at a few years ago were really just that. As far as received power flow, they were connected to the VHF and AIS in such a way as to effectively split the received energy from the antenna to both receivers (AIS and VHF) equally, which means 1/2 gets to each one.

On the transmit characteristics, I wasn't sure how these combiners are arranged. A directional coupler could be used, so that full VHF power at 25 watts doesn't end up in the AIS receiver's front end, desensitizing it from receiving AIS packets at the same time. And vice versa, so that each time an AIS packet is transmitted by the Class B AIS, it does not overwhelm the VHF radio's front end, so that conversation can continue uninterrupted.

The article is interesting, but it's not written by a radio engineer. There are a few things which can be disputed. I've seen enough LMR400 cable ripped out of masts to say that you really don't want to use that -- foam insulator -- any crushing, which is inevitable in the typical run up a mast -- will compromise the cable run by bringing shield and core close to each other. If you want to use fat cable, use RG-213 or RG-214. I personally like the RG-214, and that's what I used -- it's double shielded, and shield and core are silver plated. It's expensive but I think worth it. It has a solid dielectric which is much more resistant to crushing and water intrustion than LMR400. It has more attenuation then LMR-400, but I've already stated my opinion about the significance of that.


I do have LMR-400 on my boat -- for the fixed installed sat phone installation which came with the boat when I bought it. It's holding up OK so far, but I treat it with kid gloves. At UHF frequencies very low loss cable like LMR-400 starts to make sense despite the other drawbacks. But not at VHF frequencies.

By the way, if you do use LMR-400 for something on a boat, make sure and source the LMR-400UF version, which has a stranded (and thus flexible) center conductor. The regular LMR-400 is NOT flexible enough for a boat installation, in my experience.

As to splitters -- I wouldn't have one of those on my boat for anything. Besides attenuating the signal, a splitter adds a significant failure point which you don't need on a system which may be critical for life safety. A separate cable run and separate antenna for the AIS is the right way to do it. At the same time you gain redundancy as you can use the AIS antenna for VHF phone working in a pinch. I have my own AIS antenna on a spreader.

[EngNate]

Ditto & exactly on the LMR cable. It is not designed for this use, and I would consider it only for long runs with satellite equipment. RG-214 is the best cable for a VHF on a boat. But you will never ever be able to detect or measure the difference between it and RG-213 in your installation. And I doubt there will be any measurable difference between these and marine grade RG-8 on a 50 ft run. Dropping down to the compact RG-8X would be some compromise, but I doubt a practical difference, as in someone measuring your signal strength at x miles away. There's definitely a difference between all these and RG-58 though.

Connector installation is less reliable with the smaller cables that require a bushing. With these you want to use the connectors packaged by Shakespeare that include an insulating washer for the center conductor. It insures that a stray strand of the shield does not touch the center pin.

Tip for soldering the shield on connectors: Once the connector is on and the center pin soldered and cooled, preheat the connector with a heat gun - not too hot! - just to when you can barely grasp it, then proceed with soldering, keeping the iron tip firmly in contact with the connector, not the wire. Feed a tiny bit of solder between the tip and connector to help conduct the heat. Be patient and wait until the solder will flow on the connector on contact, then move the tip of the tip into the hole and apply solder to fill the hole. Don't disturb until fully cooled.

Sealing tape: 3M 23 Rubber Splicing Tape. The stretched wraps of this soft rubber tape seal wire connections better than anything. When stretched and wrapped it fuses to itself permanently. Vinyl electrical tape, especially the quality stuff (3M 33, 88 and the relatively cheap 700) also bonds permanently to it. All of these are usually on the shelf at Home Depot.

Note on AIS splitters: These do not divide received power in half as has been mentioned. A 2-way TV splitter does that. They are a filter array that separates frequencies, and the division power-wise depends on the content of the incoming signal. All filters have insertion loss. Except for this factor, all of the signal power present on the AIS channels is directed to one port, and all the rest to the other. But there is loss, and it varies with design and components. External splitters should have insertion loss values in their specs, you might or might not be able to obtain it for a receiver with a built in one.

[dmkkeng]

I think that for coax runs of less than 50' that RG-58CU is more than adequate, the advantage of this cable is size and flexibility. RG-8X and or RG-213 are better performing coax cables in terms of loss performance however I'm not sure you would notice the difference in the real world performance of your vhf radio. If price is no object go with the higher performance/ lower loss cables, however make sure your installation will accommodate cables with a wider diameter and less flexibility. This could be a consideration with installations that have space constraints.

Whatever cable you get, make sure it is marine quality and from a reputable manufacturer of coax cable. Also make sure you have good quality connectors that are assembled properly. If using solder type connections you have to be sure that you don't end up with a poorly soldered connection or a cold solder joint. This will impact the performance of your vhf radio far more than cable choice. Also ensure any connectors that are exposed to the elements are properly sealed to prevent water ingress and corrosion.

You can check your connector installation to ensure you do not have a short with a simple ohm meter however the true test of antenna antenna/ coax cable installation is to use a SWR (standing wave ratio) meter. This meter is connected between the output of the vhf radio and coax cable. It measures power output of the radio and power reflected back to radio that could be due to a damaged coax, improper soldered or crimped connector or improperly matched antenna. The less reflected power the better, less than 10% is acceptable however the lower the better.

In summary don't get to caught up on cable choice, get good quality components and make sure everything is performing 100%.

[Steve DAntonio]

Originally Posted by Ericson38

Steve,

Great website. Also, what do you think of the current crop of internal or external AIS splitters ? The external ones I looked at a few years ago were really just that. As far as received power flow, they were connected to the VHF and AIS in such a way as to effectively split the received energy from the antenna to both receivers (AIS and VHF) equally, which means 1/2 gets to each one.

Thank you. As someone pointed out, I'm not an engineer, just lots of technician's field experience.

I'm no fan of splitters, convenient, yes, advantageous no. AIS and VHF are too important to compromise. On all of the electronics suites I spec, I specifically prohibit VHF/AIS splitters, again there's no advantage.

[Steve DAntonio]

Originally Posted by Dockhead

The article is interesting, but it's not written by a radio engineer. There are a few things which can be disputed. I've seen enough LMR400 cable ripped out of masts to say that you really don't want to use that -- foam insulator -- any crushing, which is inevitable in the typical run up a mast -- will compromise the cable run by bringing shield and core close to each other. If you want to use fat cable, use RG-213 or RG-214. I personally like the RG-214, and that's what I used -- it's double shielded, and shield and core are silver plated. It's expensive but I think worth it. It has a solid dielectric which is much more resistant to crushing and water intrustion than LMR400. It has more attenuation then LMR-400, but I've already stated my opinion about the significance of that.


I do have LMR-400 on my boat -- for the fixed installed sat phone installation which came with the boat when I bought it. It's holding up OK so far, but I treat it with kid gloves. At UHF frequencies very low loss cable like LMR-400 starts to make sense despite the other drawbacks. But not at VHF frequencies.

By the way, if you do use LMR-400 for something on a boat, make sure and source the LMR-400UF version, which has a stranded (and thus flexible) center conductor. The regular LMR-400 is NOT flexible enough for a boat installation, in my experience.

As to splitters -- I wouldn't have one of those on my boat for anything. Besides attenuating the signal, a splitter adds a significant failure point which you don't need on a system which may be critical for life safety. A separate cable run and separate antenna for the AIS is the right way to do it. At the same time you gain redundancy as you can use the AIS antenna for VHF phone working in a pinch. I have my own AIS antenna on a spreader.

LMR isn't a hill I'll die on, it's worked for me on exceptionally long runs, and I've never had to remove any, at least that I installed, and I'd dispute that crushing is inevitable, careful installation precludes it. Agreed, UF is the right version for marine application, far more flexible.

[dmkkeng]

Splitters are a viable solution for adding AIS to your existing system. If your existing antenna is located in its optimum position on the top of the mast the splitter enables the AIS system to take advantage of the optimum antenna position. If possible installing a 2nd antenna on the top of the mast would be the best solution however the horizontal separation required makes this option prohibited. The recommendation for horizontal separation is 3-6'. The reason the top of the mast is the optimum position is it takes advantage of maximum height and a 360 degree clear path around the antenna.

A splitter and antenna at the top of the mast is a better solution than a separate antenna installed on a rail or davit mount, the significant difference in height will affect antenna performance far more than the loss created by a modern splitter. As someone already mentioned it does not split the signal in half as suggested in one post.

A better solution would be to locate the 2nd antenna as far up the mast as possible, when vertically separating antennas the distance required is less however you cannot mount the antenna next to anything metal, in fact you should be 1-2' away from anything metal otherwise the propagation pattern from the antenna will be significantly affected. The obvious mounting choice is the stanchion. Keep in mind that you will have to try to keep the antenna as far away from both the mast and rigging. If you have radar mounted on the mast you want to be at least 2' away from the radome. The advantage of the second antenna is it eliminates the splitter loss, adds redundancy and you can tune the antenna specifically to the AIS frequencies thus further improving antenna performance.

I opted for the splitter option, it simplifies the installation and from what I can tell it did not significantly affect the real life performance of my vhf radio or AIS system. Someone mentioned that it adds another single point of failure, that is true however my splitter is located close to the vhf radio, if the splitter ever fails I will bypass it and connect the coax directly to the vhf radio.

In summary the splitter is a viable solution when adding AIS to your system, the modern splitters in my opinion do not significantly affect real life performance of your vhf radio or AIS system. Yes installing a 2nd antenna is a better option however only if there is not a significant difference in height between the two antennas. For example a sailboat with a 50' mast versus installing the second antenna on the rail or davits at a height of 6-10' would be a significant difference.

[Dockhead]

Originally Posted by dmkkeng

I think that for coax runs of less than 50' that RG-58CU is more than adequate, the advantage of this cable is size and flexibility. RG-8X and or RG-213 are better performing coax cables in terms of loss performance however I'm not sure you would notice the difference in the real world performance of your vhf radio. If price is no object go with the higher performance/ lower loss cables, however make sure your installation will accommodate cables with a wider diameter and less flexibility. This could be a consideration with installations that have space constraints.

Whatever cable you get, make sure it is marine quality and from a reputable manufacturer of coax cable. Also make sure you have good quality connectors that are assembled properly. If using solder type connections you have to be sure that you don't end up with a poorly soldered connection or a cold solder joint. This will impact the performance of your vhf radio far more than cable choice. Also ensure any connectors that are exposed to the elements are properly sealed to prevent water ingress and corrosion.

You can check your connector installation to ensure you do not have a short with a simple ohm meter however the true test of antenna antenna/ coax cable installation is to use a SWR (standing wave ratio) meter. This meter is connected between the output of the vhf radio and coax cable. It measures power output of the radio and power reflected back to radio that could be due to a damaged coax, improper soldered or crimped connector or improperly matched antenna. The less reflected power the better, less than 10% is acceptable however the lower the better.

In summary don't get to caught up on cable choice, get good quality components and make sure everything is performing 100%.

Best post of the thread -- all words to live by.