Antenna (and coax) question

[N.A.]

The mast is out and the rigging being replaced, and... I suddenly have an antenna question:

For an AIS (Vesper) / VHF (Standard Horizon GX2400GPS) system (with active splitter), is there a preferred antenna?

The one on the boat is about 15" long, but practical sailor and others suggest 3 ft, about twice that (which would be about a half-wave antenna at Ch 16 frequency). My rigger, who I like, suggests a "Shakespeare 5212"; I cannot find the 5212 (probably wrote it down wrong), but it googles as a reliable brand.

--> However, I've heard AIS can be problematic on VHF antennas... is there anything I really need to watch out for here?

On a related note, coax: LMR 240 coax (googles as reliable, rigger likes) has 1.8dB loss and is 1.5 lb for my mast length and 1.5" min bending radius. LMR 400, thicker, has a 2.3" min bend radius, weighs 3 lb, and had 0.9dB loss.

If I understand that right, I get about 23% better (using the exact dB #s) reception/transmission power with the LMR 400, basically for free (coax cost not that different.) Hard to imagine why I wouldn't do this... am I missing something (maybe the bend radius is critical?)

Lastly, I have heard some LED masthead tricolors interfere with the AIS/VHF signal. Any advice here? Rigger suggests SignalMate TRIAN3C, which seems nice / googles well.

Sorry for the flurry of questions -- so much pops up the minute the work starts... As always, any advice truly appreciated!

 

[driftless]

FWIW on a similar setup - Vesper AIS with active splitter. Have gone through 3 different VHFs with it now (replaced very old original, and then upgraded to facilitate a remote mic).

I ran Ancor RG-213 coax up the mast to a 3.3' Scout KM-3A antenna. It's worked great. I've had a freighter call me by name from 18nm out so I'm getting at least that kind of range on both AIS and VHF.

I only have an anchor light up top, but it certainly doesn't seem to interfere with AIS or VHF signal while on.

I'm quite clueless about any of the physics of any of it though.

 

[N.A.]

Thanks!

I think I have narrowed in on a solution. For anyone seeing this thread in the future:

My concerns came from this article:

Special Report: How to Prevent AIS and VHF Antenna Malfunction - Practical Sailor

Since 1974, Practical Sailor’s independent testing has taken the guesswork out of boat and gear buying.

www.practical-sailor.com

Comments from the local 'experts':

Masthead lights: Apparently the issue of LED-light EMI/RF interference is not really a current one anymore. Certainly the 'Signal Mate' brand tricolors are fine in terms of EMI/RF interference as of this writing (and probably for a long time.)
PS: per the PS article, "A quick way to test for this is to tune your VHF radio to an unused channel, turn the squelch all the way down so that you can hear the receiver noise, and then turn the masthead lights on and off to see if you can hear them."

Antenna:
A "3dB", or a ~ 3' / 1m long antenna is suggested unless one is racing (here racing rule say 15" minimum). The smaller antennas are lighter (for racing), but need to be replaced more often to maintain acceptable performance, and are more omnidirectional (which I suspect means lower power to any given direction -- so need to minimize other losses etc.) A standard 3dB antenna is apparently best for boats that heel/rock like a sailboat, since higher-gain (longer) antennas are more directional and reception may go in and out to a given location as the boat rocks/heels. (Google this for discussion - lots of articles, including from Westmarine and Shakespeare antennas).
I may get an 'UltraWhip 3dB' since build quality is supposedly especially high, which sounds good for something so hard to access.
'Shakespeare' is apparently a comman / respected brand name too.

Antenna connectors:
Despite what the Practical Sailor article says, the local advice (from people who sell only the "better" type-N / TNC connectors -- is that both those and the "bad" PL259-SO239 connectors are essentially the same (if properly installed -- with dielectric grease packing or whatever is called for) in terms of longevity. It is also apparently impossible at the moment to get a TNC-connectorized 3dB antenna -- as of this writing, they are only on others (maybe the shorter racing antennas). So lucky they the standard connectors are actually ok : )

Coax:
The larger dia. coax is lower-loss (by about 0.9 dB or 23% for an 18m run), but apparently harder to work with/can be a chafe issue at the mast-top on a smaller dia mast like all of ours. People here point out that LMR 240 coax (so about 1.8 dB loss for an 18m run) is fine since a standard VHF still has plenty of power after that loss to reach the horizon* (VHF is line-of-sight), and it is sufficiently easy to route at the masthead. For a taller mast, the horizon is farther off, and the run longer, so going to lower-loss coax makes sense... but there is also extra masthead real estate to deal with it. For Ericson-sized boats, LMR 240 is the recommended diameter to use.

Coax (II): there is regular LMR brand coax, with a copper braid, and "lightweight" LMR LW coax with an aluminum braid. See the PS article for comments on the issues connecting to the LW type. My take-home is that you really want someone used to working with LW to do that connecting work, not just someone familiar with normal LMR. Not sure the difference matters other than for racers super concerned about weight.

Mast-base Splice: once can do a 'mast base splice' at the (obviously) end of the coax at the mast base to make it easier to disconnect later if you ever have to pull the mast. Not sure if this is a splice to a connector there, or what. If one is using LMR LW, with the more complicated crimping /soldering issues, then it would probably make sense to get this mast-base splice done by a pro so that any later work would happen with "normal" coax.

Aside (from me): AIS and VHF: looks like AIS is at 162 MHz and Ch 16 VHF at 156MHz. Thus an antenna tuned for maximum efficiency at ~ 159 MHz, so it is equally rolled-off in efficiency at 162 and 156, is probably best. And one wants enough bandwidth (BW) to span those extremes without efficiency dropping too far. I find most antenna manufactures provide some (or none) but not all of these specs, so good luck...

* Horizon: Bowditch and other refernces have the formula for the geometrical horizon as d (in nm) = 1.22 * sqrt(h (antenna in feet)). So for my ~ 53' clearance thats almost 9 nm, and for a freighter with a 68m high antenna (big cargo ship) d ~ 18nm, so in principle you might want your VHF power (radiated) to be sufficient to reach 27 nm. The ~23% gain from using LMR 400 vs LMR 240 coax might matter at the extremes of this, but it is hard for me to know how much. Best case it would add about 2.4nm if your VHF reached 24nm (since power will drop with 1/r^2, so 23% more power would reach about 11% farther.) Of course, 2.4nm larger VHF radius is a lot (r^2 again) more ocean if you're talking about area over which you'd see stuff on AIS, so you'd be back to a 23% improvement there.

 

[Nick J]

LMR is great stuff, but for marine applications I think the Anchor RG213 is better. LMR 240 and 400 use foam dielectric that's susceptible to being crushed during installation. When that happens it results in the center conductor being closer to the shield which increases reflected power and reduces the power that's actually making it out of the antenna. the Anchor RG213 uses solid polyethylene dielectric and tinned copper. In a perfect world, it wouldn't matter because everything would be sealed up and water would never get in, but it is a boat.

High quality PL259 connectors installed correctly will be more than adequate for this application. I've tried multiple times to take the quick and easy route and order generic ones on Amazon, but almost all of them have some kind of manufacturing defect that make them next to impossible to install. I've had good luck with Pan Pacific UHF 7606 connectors (Rod Collins recommends these on his Marine How To page). Although these use crimps for both the center pin and shield, filling the center pin with solder is easy and a good improvement.

I've tried a few crimpers, but these ones seem to work well with the connectors listed: https://www.amazon.com/dp/B08VV71QC...2JQ2MJ6UMDHFD&ref_=aip_sf_list_spv_ofs_d_asin.

Any connectors, regardless of how nice they are, will attenuate the signal and be a potential point of ingress for water. The fewer you have in the run the better. instead of using a mast base connector, add a service loop then take it directly back to the radio or ais splitter. When it comes time to remove the mast again, just cut the service loop and install connectors at that time. Yes, you end up with a connector at the base of the mast eventually, but the initial install will be better.

I went with the GAM-SS-2 mini antenna. When I purchased it, it was sold with a long whip that you cut down to size depending on the what frequency you wanted to use if for. It looks like they are now sold pre cut for 159mhz.

Here's how our installation turned out:



The whole system had a VSWR of 1.2 at 159 MHz. It's been performing well so far.

 

[bgary]

FWIW, I went with the whole Vesper setup - Vesper's splitter and Vesper's antenna, with an ICOM VHF in the mix.

And although I started out planning to use LMR-400, I ended up using LMR-240 largely because of weight/bulk/bendability. The (very small) tradeoff in loss has not been noticeable. System has been working great, no issues.

 

[southofvictor]

The fewer you have in the run the better. instead of using a mast base connector, add a service loop then take it directly back to the radio or ais splitter

FWIW in our 38-200 I was able to get the mast coax and connector through conduit leading to a starboard locker behind the settee back along with the wind instrument wire I pulled in October. Making the connection there seemed less impacted by moisture than under the mast. It’ll mean a little extra work to pull wires when we pull the mast but the tradeoff felt worth it.

 

[Nick J]

FWIW, I went with the whole Vesper setup - Vesper's splitter and Vesper's antenna, with an ICOM VHF in the mix.

And although I started out planning to use LMR-400, I ended up using LMR-240 largely because of weight/bulk/bendability. The (very small) tradeoff in loss has not been noticeable. System has been working great, no issues.

Bruce, I used your blog as a guide when i was planning it out. Unfortunately the Vesper antenna wasn't available then. It was right around the time garmin was purchasing Vesper.