N Connectors

[Red Sky]

The February issue of Practical Sailor, page 2, “Man Overboard Update for AIS”, mentions the use of the “N” connector for a more rugged/weatherproof VHF antenna installation. Any real world experiences available?

[Jammer]

They're the gold standard for outdoor use. I've bought dozens of them over the years for RF labs I've fitted out for my day jobs. They are what I use for the amateur radio station I am presently building in my basement. They've been available for decades, and are widely considered to be better mechanically and electrically than the PL-259 "UHF" connectors you've probably seen on marine VHF equipment and CB radios. Also have power handing capabilities well over 1000 watts in most frequency bands. They are available for almost any kind of coax or heliax you might want to use.



Drawbacks. They're big and expensive, and there are smaller and cheaper alternatives. They are lossy at the higher end of the microwave spectrum so above around 5 GHz (5000 MHz) or so there are probably better choices. There are better choices for very high power transmitters, over 1000 watts at VHF or over around 10,000 watts HF. I believe they only come in 50 ohm characteristic impedance, so for things like cable TV that use 75 ohm they are a poor choice.


But they are what you would find for most cellular carrier installations, or land mobile radio (public safety/dispatch) installations, or pager base stations, or cable TV head ends, or for the portions of broadcast stations that don't involve high power.


Right now I just have a handheld on my small sailboat. Next boat, the communications plumbing will all be with Heliax and N connectors.

[Dsanduril]

+1 to Jammer's comments. N-connectors are pretty much all that gets used for outdoor professional installations from HF to 2.4GHz in the types of power ranges we use on boats. Much easier to waterproof (or buy in a truly IP67 version) than a PL259. Slightly larger diameter (~20mm vs ~18mm) but usually also shorter, so depends on how/where you have to pull it.

There are both 50 and 75 Ohm versions, they should not be mixed, the center pin diameters are different. Some (usually cheaper versions) are not marked and it is possible to mix the two and get a poor RF connection. Take care in making sure you purchase matched (and probably 50 Ohm) sets. 50s are general radio, 75s are cable TV.

[Red Sky]

Thanks Jammer & Dsanduril, I did a quick look online and couldn’t find a male plug that cost more that $20, virtually the same price as a high end PL-259. Why then are they not the standard for marine use? Something I’m missing?

[Dsanduril]

One of those great mysteries of life. The industry standardized decades ago on PL259 and now it would be difficult to use something different. The N is better at the masthead, but most VHF antennas come with a 259. Same with most radios (although indoor probably not nearly as critical, we all hope the back of our radios doesn't get wet).

[Dockhead]

I use "N" connectors wherever possible, but even better than an "N" connector is a straight run of cable without a joint


My VHF antenna is connected to the RG214 main feedline with an "N" connector, and I eliminated the joint at the base of the mast, and ran the cable all the way to the nav table. There you can't avoid an SO/PL259 because that's the only connector modern VHF sets are equipped with




My VHF antenna (a Shakespeare Galaxy internal dipole) came with a pigtail and PL259, but I chopped that off and installed a Type "N". No way did I want a PL259 at the top of the mast

[Jammer]

Originally Posted by Red Sky

Thanks Jammer & Dsanduril, I did a quick look online and couldn’t find a male plug that cost more that $20, virtually the same price as a high end PL-259. Why then are they not the standard for marine use? Something I’m missing?

Nope, just history and market inertia.


The PL-259 was widely used on radio equipment in World War II. All the gear was dumped on the surplus market after the war was over and became a de facto standard among hobbyists in the postwar years. Commercially made amateur radio and CB radio equipment used the same connector. When marine VHF radios became a thing they used it too.


And in practice they're fine at VHF in a dry environment. In those days the radios themselves weren't sealed. Antenna wise the usual approach was to avoid any connectors at all, as Dockhead indicates, or at least to have them below decks where they would stay dry.


But with N connectors there's really not a reason to have the inconvenience of no connector at the base of the mast. Properly installed, they'll last the life of the coax, and there's not any loss to speak of, and they save wear and tear on the coax. They also allow for a switch between coax types. I don't know why more people don't use Heliax in the mast, then switch to more flexible 214 (but heavier and more expensive) to go from the mast base to the radio.

[Dockhead]

Originally Posted by Jammer

. . . But with N connectors there's really not a reason to have the inconvenience of no connector at the base of the mast. Properly installed, they'll last the life of the coax, and there's not any loss to speak of, and they save wear and tear on the coax. They also allow for a switch between coax types. I don't know why more people don't use Heliax in the mast, then switch to more flexible 214 (but heavier and more expensive) to go from the mast base to the radio.

Some people need a connector at the base of the mast -- if you need it, then obviously N is the way to go. But in my opinion it's a bad place for a connector -- likely to get wet, and every connector, even an N, has insertion loss, and every connection is a potential faulty connection. It's really good to avoid it if possible.


As to Heliax (LMR400) -- I don't personally like the idea of foam core coax in the marine environment, and especially not in the mast, where the cable even if well secured will inevitably get banged around. All it takes is one dent in it to compromise the electrical qualities, and what if water gets into the open cell foam used in LMR400? LMR400 is admirably efficient, and is also lighter and cheaper than RG213 or RG214, but is it worth the risk for a life safety critical device like the VHF? RG214 is double shielded, and with silver coated copper shields and silver coated center conductor. LMR400 has got a lot of untinned copper and even bare aluminum in it -- I have doubts about whether it will hold up well in the marine environment, leaving aside the question of the foam core.

[Jammer]

LMR400 would be a poor choice on a boat due to its aluminum construction.


Heliax is not the same. While it does have a foam dielectric, it is all copper and the continuous outer conductor provides another layer of protection against water ingress. It is lower loss than LMR-type or RG-type cable of the same size, and lightweight. Due to its corrugated construction, it is not particularly susceptible to dents.



https://www.rfparts.com/fsj2-50.html


To be sure, RG214 is great stuff, too, but it has twice the loss of 3/8" heliax and is 15x (!) heavier.

[Dockhead]

Originally Posted by Jammer

LMR400 would be a poor choice on a boat due to its aluminum construction.


Heliax is not the same. While it does have a foam dielectric, it is all copper and the continuous outer conductor provides another layer of protection against water ingress. It is lower loss than LMR-type or RG-type cable of the same size, and lightweight. Due to its corrugated construction, it is not particularly susceptible to dents.



https://www.rfparts.com/fsj2-50.html


To be sure, RG214 is great stuff, too, but it has twice the loss of 3/8" heliax and is 15x (!) heavier.

Learn something every day. Thanks!

[Red Sky]

Thanks everyone. The reason I ask is, the mast was down for new standing rigging and I replaced the coax and antenna with a VHF/AIS antenna from Vesper. I was very careful to weatherproof the connection at the antenna, but when they stepped the mast, they disconnected the coax and turned the antenna upside down. They did reinstall it, but I wasn’t able to inspect it. The work was done by what I consider the top yard in the S. F. Bay, but...

What do you guys think? My inclination is to get my electronics guy up the mast to change it out to an “N”, if he goes aloft, which I don’t know if he does or not.

[Jammer]

Did they do anything to waterproof it? If they put good heat shrink over the connection, or good tape, it will probably work fine for a long time. If not, it will still work for a while. I would not necessarily replace it right away. Maybe the next time you're up the mast, or have the mast down. (You do have another VHF antenna somewhere, don't you?)

[Red Sky]

They said they retaped it and from the ground with binocs it appears so, but...My worry is, by the time there’s a problem, the braid will be so compromised that I’ll have to pull a good amount of coax out of the mast to get some that’s not corroded. The mast will not come down while I own this boat, at least not on purpose. For me, it’s tough enough soldering a connector for the radio end in the protection of the cabin, up a mast, no way.

I have two, 6’ & 3’ and enough coaxial to get one or the other onto the dinghy davits or rail.

I’m going to contact the electronics guy here in Alameda and discuss. Thanks again for your input.

[SoonerSailor]

It is quite possible, and not hard, to fully weatherproof a standard PL-259 connection with the proper self-fusing tape. I've done that many times, on the boat and on land, with no moisture intrusion failures or detection on disassembly. Yes, an N connector is inherently far more weatherproof from the start and easier to complete a hermetic connection with, but you can do it with the standard UHF connectors. Whether your guys did it really well or not, that is your conundrum.