VHF/AIS antenna -radio geek advise needed

[Sailing Ohm]

Hello y’all, I know there is plenty of discussion on this forum about antennas but I’d like some specific advise please.
I recently replaced a very very old vhf radio with a gx2400 that is also an ais receiver and does dsc calls.(one day I’ll add a full blown ais transponder when the budget allows it)

-My VHf antenna is the standard Shakespeare 3ft whip mounted on the masthead, along with the usual other masthead attachments. It has older ancor marine RG-58c/u coax cable and is probably a 70’ cable run (mast is 50’ and I estimate 20’ in the cabin to the vhf). I’m not sure of current max range but the ais only picks up boats max ~3nm (although it does have a limit of displaying 15targets and I’ve only used it in the anchorage not open water so maybe that’s why) but I suspect the old cable and poorly installed pl-259 connectors.
-I’ve tried to pull the old coax through the mast from the top and bottom but it simply won’t budge an inch and taking the mast down is something I’d like to avoid for both high cost (haul out and crane costs could easily exceed $800 not to mention cost of hardware) and complexity.

My question is, since RG-58 has a high attenuation (pretty sure I’m using that term correctly /let me know if I’m not) would there be a noticeable increase in VHF/AIS range if I mounted a 8’ (maybe 12’?) antenna off of my solar arch and ran LMR-400uf to it?
Solar arch is about 10’ above waterline.
- Would this be a prudent investment?
- If y’all think so would it be better to get an antenna with a higher db since the effect of pitching would be less than at the masthead?

Thanks in advance for the info and your patience as I am just getting into understanding the intricacies and nuances of radio.

[rslifkin]

I would definitely replace the cable up the mast with much better stuff. Having the antenna up high will help range more than a higher gain antenna.



Personally, I'd stick with a good 3db antenna up top with the best coax you can put on it, then when you add a separate AIS transponder or a second VHF, maybe give that one a 6db (8 foot) antenna on the arch. It won't have the range of the masthead antenna, but should still be more than enough for AIS.

[thomm225]

VHF range would decrease with that short antenna as I doubt the attenuation is that significant but the decreased height would definitely decrease VHF range.

I hooked my SH GX2200 VHF with AIS/GPS to my ancient mast head VHF antenna cable last year, and it works great.

Also your old VHF radio and the new one probably have the same wattage for TX around 25 watts so they should work about the same. My old SH Intrepid had a range of 15 miles plus.

AIS targets to almost 30 miles out and no decrease in VHF range that I have noticed.


If all else fails, hook it up and see how it does. That takes about 10 minutes max.

[Dockhead]

You care more about antenna height than power, so I would not move your antenna to the arch.


If you can't change the coax in the mast (can you pull a new one, while leaving the old one in place?), then I would install new connectors, taking care to get it perfect, and hire a pro if you are not 100% sure of your ability. If you have a disconnect at the mast base, use Type N there.


And I would install a good antenna, which makes a big difference. The Shakespeare Galaxy is a particularly good one -- it's an internal dipole so doesn't need a ground plane, which is problematic for many antennae.



And just change the coax next time you have the mast down.


I would not use LMR-400 which has a foam insulator and is vulnerable to crushing inside a mast. And may be vulnerable to water intrusion. I use RG-214, with a solid insulator, which is similar to RG-213 with silver-plated shield. Slightly more attenuation (yes, you used that word correctly ) than LMR-400 but much more rugged.



And if you can't easily use a fat coax like that, then RG8X is fine. Attenuation in the feedline is not really a big problem at VHF frequencies, considering that fixed installed marine VHF sets are grossly overpowered at 25 watts. This is by design. The big issue with these installations is almost always either the connectors, or the antenna (particularly grounding problems). Sometimes there is a fault with the coax, but much less often than with the connectors. So I think if you will change all the connectors and install a good antenna, you should be fine.


My mast is 75 feet tall, but with a good installation (no connectors at the mast base; Type N at the top and carefully soldered PL259 at the radio), and a good antenna, I get good radio checks at 60 miles (!) -- using 1 watt transmission power (!!), which is how I normally keep my radio set. 25 watts is plenty to burn through whatever attenuation you have in your feedline provided you get the connectors and antenna right.

[Dockhead]

Originally Posted by rslifkin

. . . then when you add a separate AIS transponder or a second VHF, maybe give that one a 6db (8 foot) antenna on the arch. It won't have the range of the masthead antenna, but should still be more than enough for AIS.

That's good advice. Separate AIS antenna and feedline is a really good idea for different reasons. Only, buy an antenna specially cut for AIS frequencies (about 162mhz); normal marine VHF antennae are cut to be optimum on 156.8mhz and are sub-optimal for AIS. Doesn't need to be 8 feet with the attendant windage -- one of these is fine: https://shakespeare-ce.com/marine/pr...f-ais-antenna/



I agree that height of the AIS antenna is not very important. The AIS antennae on ships will be very high, so you will see each other from 10+ miles away in any case. My AIS antenna is on my first spreader, 10 meters above the water surface, but even less than that is fine.

[Sailing Ohm]

Originally Posted by Dockhead

You care more about antenna height than power, so I would not move your antenna to the arch.


If you can't change the coax in the mast (can you pull a new one, while leaving the old one in place?), then I would install new connectors, taking care to get it perfect, and hire a pro if you are not 100% sure of your ability. If you have a disconnect at the mast base, use Type N there.


And I would install a good antenna, which makes a big difference. The Shakespeare Galaxy is a particularly good one -- it's an internal dipole so doesn't need a ground plane, which is problematic for many antennae.



And just change the coax next time you have the mast down.


I would not use LMR-400 which has a foam insulator and is vulnerable to crushing inside a mast. And may be vulnerable to water intrusion. I use RG-214, with a solid insulator, which is similar to RG-213 with silver-plated shield. Slightly more attenuation (yes, you used that word correctly ) than LMR-400 but much more rugged.



And if you can't easily use a fat coax like that, then RG8X is fine. Attenuation in the feedline is not really a big problem at VHF frequencies, considering that fixed installed marine VHF sets are grossly overpowered at 25 watts. This is by design. The big issue with these installations is almost always either the connectors, or the antenna (particularly grounding problems). Sometimes there is a fault with the coax, but much less often than with the connectors. So I think if you will change all the connectors and install a good antenna, you should be fine.


My mast is 75 feet tall, but with a good installation (no connectors at the mast base; Type N at the top and carefully soldered PL259 at the radio), and a good antenna, I get good radio checks at 60 miles (!) -- using 1 watt transmission power (!!), which is how I normally keep my radio set. 25 watts is plenty to burn through whatever attenuation you have in your feedline provided you get the connectors and antenna right.

Thanks for the information! Especially about 25watt vhf sets being overpowered for the task which compensated for attenuation and a secondary antenna for an ais transceiver when I get there.

I recently replaced the old vhf antenna (it got too close to a bridge...not by me lol) with the Shakespeare 5215 (https://shakespeare-ce.com/marine/pr...-antenna-copy/) which says it doesn’t need a ground.

I did not address the coax connectors.
Would you recommend the Shakespeare “crimp on” style gold connectors? They seem pretty fool proof especially when working at the top of the mast. Expensive but that’s the price of easy if use.

So it sounds like if I replace the both ends of connectors all should likely be good unless there is some damage to the cable itself in which case somehow running a new cable (drop it down and fish it out I guess...) is the next step.

Thanks again y’all.

[Captain Bill]

What Dockhead said about the 8ft VHF 6db antennas being suboptimal is correct. I recently went through the same process and a cheap 8ft 6db antenna ($80) resulted in an swr above 2 which is not great. Some 8ft 6db antennas are tuned to be good over a 6mhz bandwidth(156-162mhz), but they cost more ($160+) Just make sure whatever you buy is good to 162 mhz. Oddly I got a very good swr (1.5)from a 3ft whip antenna at the mast head at 162 Mhz with 80 ft of RG8x. If you are going to use a dedicated AIS antenna on the arch get one optimized for 162 Mhz or use a whip antenna. The 3db whips won't be as directional but because their output is radiated in a sphere they will get out when heeling. It's not important on my cat but your could be dumping a lot of your 2 watt AIS transmission into the ocean and sky with a 6db antenna when you want to be sending it to that tanker bearing down on you, if you've got a bit of a heel going.

[Bycrick]

The Shakespeare screw-on connectors are worthless on a boat around salt water. No matter how well you "think" you sealed them, they’ll corrode and fail in a few months. Look on Maine Sail's web site for some of the horror stories. I’ve seen the same problems.

[Differentroads]

I put a seperate AIS antenna on a pole at my stern, just a 3' whip about 10' abov sea level. It gives me reliable reception from ships 20 to 30 miles distant. I'm really only interested in keeping an eye on ships 10 miles or less away though.
The key benefit of a seperate AIS antenna is as a backup for the vhf radio if the masthead one fails. And thats why I didn't have mine retuned (cut a little bit shorter) for the AIS frequency. Best performance on channel 16 if I have to use the AIS aerial as a backup is more important to me.

[Differentroads]

Re poor AIS reception range on your masthead antenna. I get no better range in my marina surrounded by a forest of masts and a high sea wall. Nor did I in a previous marina which had a hill between my boat and most AIS carrying vessels. So that might not be a cause for concern. On the other hand, it could indicate a problem with the cable or connectors. What sort of range do you get on a test transmission?

[Sailing Ohm]

Originally Posted by Bycrick

The Shakespeare screw-on connectors are worthless on a boat around salt water. No matter how well you "think" you sealed them, they’ll corrode and fail in a few months. Look on Maine Sail's web site for some of the horror stories. I’ve seen the same problems.

Good to know thanks

[Sailing Ohm]

Originally Posted by Differentroads

Re poor AIS reception range on your masthead antenna. I get no better range in my marina surrounded by a forest of masts and a high sea wall. Nor did I in a previous marina which had a hill between my boat and most AIS carrying vessels. So that might not be a cause for concern. On the other hand, it could indicate a problem with the cable or connectors. What sort of range do you get on a test transmission?

I tried to do the US coast guards DSC test call but I got no reply on two separate occasions although I’ve read this isn’t uncommon.
Still reading up on all of this as it’s all new to me. Trying to avoid sending out a distress call or do something I’m not supposed to.

I’ve been using bridge opening calls to figure out vhf range and I pick up bridge chatter 8-10 mi away with quite a few tall buildings in between the bridge and I. I’m assuming this is acceptable under the circumstances but again I don’t really know. (The handheld vhf doesn’t get them so it’s at least better than that).

I am ordering some new connectors and I’ll probably order some new cable (prob RG-213 with pre installed pl-259s) while I am at it. My plan is to replace the connectors and then retest.
If nothing changes/improves I’ll run the new cable outside the mast as a test. I should have my answer then.

I am due for a haul out in the next year for bottom paint so if I need to pull the mast to rerun the coax so be it...I’ll start saving cash now. That’ll be a new adventure though.

[Differentroads]

Originally Posted by Sailing Ohm

I tried to do the US coast guards DSC test call but I got no reply on two separate occasions although I’ve read this isn’t uncommon.
Still reading up on all of this as it’s all new to me. Trying to avoid sending out a distress call or do something I’m not supposed to.

I’ve been using bridge opening calls to figure out vhf range and I pick up bridge chatter 8-10 mi away with quite a few tall buildings in between the bridge and I. I’m assuming this is acceptable under the circumstances but again I don’t really know. (The handheld vhf doesn’t get them so it’s at least better than that).

I am ordering some new connectors and I’ll probably order some new cable (prob RG-213 with pre installed pl-259s) while I am at it. My plan is to replace the connectors and then retest.
If nothing changes/improves I’ll run the new cable outside the mast as a test. I should have my answer then.

I am due for a haul out in the next year for bottom paint so if I need to pull the mast to rerun the coax so be it...I’ll start saving cash now. That’ll be a new adventure though.

I bought the boat I now live and cruise on ten years ago. One of the jobs I did on my first winter haul out was have the mast taken off. I replaced all of the mast wiring (only one wire showed the blackening of the copper wire that shows water had got in but I took that as a sign to replace the lot.) At the same time I DIY replaced all of the standing rigging, added a couple of extra blocks at the top of the mast and fitted a new VHF antenna. It felt like a bit of an adventure, doing stuff I'd never done before, having to learn fast and solve problems.
Good luck to you on your own adventures 🙂

[ka4wja]

Sailing Ohm,
I'm a longtime "radio nut", as well as having made my living in the communications business for many decades....
So, I hope to be able to help you out...

1) See below for some specific answers to your questions...
But, please do NOT use those weird crimp-on Shakespeare connectors!

And, please conform you're in West Palm Beach....(fyi, using NOAA Weather radio stations as a general guide, you should be able to receive at least THREE all the time, there in WPB....and many times FIVE....and sometimes SIX....if you're not getting at least TWO, you definitive have a VHF antenna / cable / connection issue!)


2) But first, some general facts-of-life:

a) Marine VHF Antenna Height / Coax Loss?
Height trumps everything else!


Whether VHF-FM (voice), VHF-DSC (data), or AIS (vhf data), height trumps all!

Height is significantly more important than coax loss, and/or antenna gain, and/or transmit power....

Unless there is a very large difference involved, such as an old piece of coax and connectors which has a loss of 20 - 30db, etc....well, of course, then that would take precedence....but, except for an extreme case such as this (the situation you might have), height trumps all!



b) If you'd like details of all of this, as well as many details of VHF Radiowave Propagation, coax losses, Marine VHF link budgets, etc....please have a look at these threads:

VHF and AIS Radiowave Propagation and VHF and AIS Radio Range
https://www.cruisersforum.com/forums/f13/vhf-and-ais-radiowave-propagation-and-vhf-and-ais-radio-range-149499.html

Vesper AIS SP-160 "relay/splitter" test results, lab/real world

https://www.cruisersforum.com/forums/f13/vesper-ais-sp-160-relay-splitter-test-results-lab-real-world-130803.html



c) Stick with a simple 3' SS whip antenna....or, if you desire a more rigid antenna, select a simple 3' - 4' fiberglass radome-covered "3db" antenna...you will not notice much (any) improvement versus a higher gain antenna, but....but, as a higher gain antenna is taller, when it is mounted low (such as on a stern rail) you can see an improvement, even though that improvement is due to height, not actual antenna gain...



d) Many boats have a "disconnect" point in the bilge / near the mast step, where the mast wiring runs.....this allows un-stepping the mast, without ripping out lots of wiring inside the boat!!!

And, tied for first place in the "VHF range issue" causes are:
--- bad mast step / bilge coaxial splice (usually, each piece of coax, one from radio and one from masthead, have their PL-259 male connectors screwed onto a PL-258 "double-female" barrel connector....and it could be one, two, or all three of these at fault....and fyi, it can also be that these connections are now dry, but water/moisture has gotten in there and "wicked-up" inside the coax, rendering it all but useless....)
--- bad masthead coaxial connection....again usually caused by poor weatherproofing....and again, while the connection may be dry upon inspection, as above water/moisture has probably gotten in there and "wicked-up" inside the coax, rendering it all but useless....

---- In "second place" is just old / poorly installed coax and connectors....

---- And, in "third place" is bad/old (blown-up) VHF antenna...



3) Okay....specifics...

a) Old coax and old connections (and an old antenna?) are always suspect....and many/most "VHF range issues" (whether VHF-FM Voice, VHF-DSC, or AIS) are directly related to old/bad coax and connections!

Many times, the antenna at the masthead is not even connected, or the connection is corroded/filled with moisture....the coax and the tiny stub of the connector is actually what is acting as your "antenna"....

Look in the bilge for your cable splice / connections, first.....then go up the mast and look at the masthead coax connections....if all these look good (and test okay), then assume you'll need to replace the cable and connectors and in the mean time you can install a stern-solar-arch mounted antenna (with some new coax), and you'll be good to go!



b) Can you buy new coax, with pre-assembled connections? Yes, of course....and DX Engineering sells excellent cable w/ assembled and tested connectors....so, if you can fit a 0.405" diameter cable thru your mast conduit, then RG-213 is an excellent choice....(steer clear of "low loss" cables such as LMR-400uf...)

https://www.dxengineering.com/search/brand/dx-engineering/part-type/coaxial-cable-assemblies/product-line/dx-engineering-rg-213u-pl-259-low-loss-50-ohm-coax-cable-assemblies?autoview=SKU&sortby=DisplayPrice&sortor der=Ascending




c) Can you buy new coax with pre-assembled connectors, and a new antenna, and mount it at 10' off the water, and be successful? Yes, of course you can....buy a 25' (?) length of RG-213, with connectors professionally installed, and a new Shakespeare 3' SS Whip (5215-AIS, etc.)....and mount it on your "solar arch", and you'll find good results! (and the 3' SS whip shouldn't shadow your solar array either, so no worries there...)

https://shakespeare-ce.com/marine/product/5215-ais-with-vhf-squatty-body-antenna/

https://shakespeare-ce.com/marine/product/5215-classic-vhf-squatty-body-antenna-copy/



d) A stern-rail / solar-arch mounted VHF antenna in addition to being a quick / temporary solution (until you can replace the coax in the mast), also gives you a second/redundant VHF antenna, which you can use for an AIS transponder (transmitter) or a second VHF radio....or as a "spare" VHF antenna, should you have issues with the masthead antenna!




I hope this helps clear things up?

Fair winds.

John

[Sailing Ohm]

Originally Posted by ka4wja

Sailing Ohm,
I'm a longtime "radio nut", as well as having made my living in the communications business for many decades....
So, I hope to be able to help you out...

John

Thanks for all the info John! You always seem to provide a lot of good answers to radio questions.
To answer your question, Yes I am in WPB and I do pick up three weather stations, albeit only one is consistently clear. I can make out what’s being said on the other two but lots of static. With squelch adjustment a second comes in sort of clear but with any squelch adjustment the third is just totally lost.

Hopefully this week I’ll get a mast climb in and be able to check the connectors.