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Old 30-09-2019, 15:32   #1
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Trying to find the perfect VHF antenna

So, I have decided to upgrade my VHF antenna as the performance is terrible. I currently have a masthead antenna around a metre tall connected using about 18m of RG58U cable. The antenna is one of those fold-down ones with a metal hemisphere on the antenna that is clamped to a metal hemisphere in the base. A stupid arrangement that just invites corrosion and who is going to fold down an antenna at the top of a mast? I did some calcs on the RG58U cable and my 25W from the radio would be less than half by the time it gets to the antenna. Add in some corrosion on the antenna base and no wonder nobody can hear me.

So, the solution is clear, I need better coax cable, preferably LMR400 but at least RG213. I need an antenna with connections that can resist corrosion.

The trouble is that I simply can't find an antenna and/or base that will accept the thick coax i need to use.

Any suggestions?
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Old 30-09-2019, 16:28   #2
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Re: Trying to find the perfect VHF antenna

The antenna "base" is a SO-239 which is standard on the majority of VHF antennas. And, the connector on the coax is PL-259, or commonly known as a UHF connector. That too is standard. So I don't think that will be an issue.

The VHF antenna is also by choice. I am sure most will say that they use "x brand" and have had no issues. So I guess it will be up to you to get what most sailors use. As for the actual mount, yeah, need to screw or rivet to the mast. Make sure all parts match the material of the mast to prevent corrosion.

Cable length is subject to the attenuation per foot or meter in your case. 18 meters would be about half so regardless of what cable you use, the attenuation will reduce your signal.

Good installation practice will prevent poor performance in the long run. So don't skimp or connectors or mounts.

As always, JMHO.
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Old 30-09-2019, 16:51   #3
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Re: Trying to find the perfect VHF antenna

It’s typically not the coax loss or the antenna which prevents effective radiated power but rather bad or corroded connectors. Or both. If the coax is old, it’s probably good to replace it too but focus on making good soldered connections on the PL259s as your most likely problem. Crimp connectors if not done perfectly and with the proper crimped will fail.
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Old 30-09-2019, 22:04   #4
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Re: Trying to find the perfect VHF antenna

18m of 58u is pretty bad. That is too small for that length.

Something like a Shakespeare 5215. Takes any cable.
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Old 01-10-2019, 02:03   #5
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Re: Trying to find the perfect VHF antenna

If you want AIS too, check if the antenna had any issues with AIS. Not typical, but you can run into a mistuned antenna, like this Shakespeare unit:
https://www.thehulltruth.com/8840429-post19.html
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Old 01-10-2019, 03:37   #6
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Re: Trying to find the perfect VHF antenna

Quote:
Originally Posted by Brian.D View Post
The antenna "base" is a SO-239 which is standard on the majority of VHF antennas. And, the connector on the coax is PL-259, or commonly known as a UHF connector. That too is standard. So I don't think that will be an issue.

The VHF antenna is also by choice. I am sure most will say that they use "x brand" and have had no issues. So I guess it will be up to you to get what most sailors use. As for the actual mount, yeah, need to screw or rivet to the mast. Make sure all parts match the material of the mast to prevent corrosion.

Cable length is subject to the attenuation per foot or meter in your case. 18 meters would be about half so regardless of what cable you use, the attenuation will reduce your signal.

Good installation practice will prevent poor performance in the long run. So don't skimp or connectors or mounts.

As always, JMHO.

Well all correct in MHO as well.


I replaced the old coax in my mast with RG213 and the antenna with a regular off the shelf Standard Horizon, 3' based loaded SS whip. Works great. Just buy the proper sized AMP PL259 connector for the RG213 cable for the installation.



I prefer soldered connections but doing a proper solder job on one of these takes the proper tools and can be a bit tricky. If you aren't 100% on your ability to do this follow the instructions at this link.


https://marinehowto.com/easy-vhf-terminations/
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Old 01-10-2019, 04:11   #7
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Re: Trying to find the perfect VHF antenna

Quote:
Originally Posted by Cliffhanger View Post
So, I have decided to upgrade my VHF antenna as the performance is terrible. I currently have a masthead antenna around a metre tall connected using about 18m of RG58U cable. The antenna is one of those fold-down ones with a metal hemisphere on the antenna that is clamped to a metal hemisphere in the base. A stupid arrangement that just invites corrosion and who is going to fold down an antenna at the top of a mast? I did some calcs on the RG58U cable and my 25W from the radio would be less than half by the time it gets to the antenna. Add in some corrosion on the antenna base and no wonder nobody can hear me.

So, the solution is clear, I need better coax cable, preferably LMR400 but at least RG213. I need an antenna with connections that can resist corrosion.

The trouble is that I simply can't find an antenna and/or base that will accept the thick coax i need to use.

Any suggestions?

A number of suggestions. You are on the right track using LMR 400 or RG213. I'd add RG214 to that mix (better shielding than RG213). Use silver-Teflon solder-solder connectors. Most definitely NOT the Shakespeare crimp connectors at West Marine. Properly installed connectors with an adhesive-lined shrink boot are important. Ask if you need guidance on soldering the connectors. I get coax and connectors from Joel at RF Connection (http://rfconnection.com); tell him I sent you.



The most important physical characteristic of an antenna is to have a fixed connector at the base of the antenna. NOT a flying pigtail. I also prefer a metal whip over the fiberglass radome type, mostly for bridges. I like the Metz Manta 6. There are lots of alternatives.


You can screw or rivet the antenna mount to the mast. I have a mild preference for machine screws, either 10-24 or M5 as both are common for minor mounting duties on boats. You can get matched drill and tap sets. Get a batch (another reason for being consistent in sizing). You'll want to use Tef-Gel or lanolin between the stainless steel screw and the aluminum mast to avoid corrosion welding.



I also suggest avoiding a connection at the base of the mast. Just run the coax directly to the radio, leaving a loop of slack at the mast. If you're careful about the coax routing you can just pull it back when you have to remove the mast someday. If you have to you can cut the coax at the slack loop and add connectors and a barrel but avoiding that is a good thing.


Putting a connector on coax at the masthead is awkward. You only have to try once to know it's a bad idea. Put the connector on at the ground and haul the whole thing up the mast. Feed the coax down through the mast, make up the coax to the antenna, and come down. Route the coax inside the boat and install the connector on the radio end.



Best wishes.
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Old 01-10-2019, 06:04   #8
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Re: Trying to find the perfect VHF antenna

Quote:
Originally Posted by S/V Illusion View Post
It’s typically not the coax loss or the antenna which prevents effective radiated power but rather bad or corroded connectors. Or both. If the coax is old, it’s probably good to replace it too but focus on making good soldered connections on the PL259s as your most likely problem. Crimp connectors if not done perfectly and with the proper crimped will fail.

That's right and really important.


You will not get "terrible" radio performance just because you use RG58, which is perfectly reasonable cable.


Pulling coax through a standing mast is a PITA. I would cut off the top connector and see if the cable is degraded. If not, I would leave it in place and concentrate on PERFECT connectors. It's a bit of an art to do good soldered connections, and with a high failure rate even among people with experience, so you might want to consider hiring a pro to do pro quality crimps. Chop em all off and put on new ones, perfectly.



Then a good antenna won't hurt anything; and best not to use one which needs to be grounded. I use a Shakespeare Little Galaxy with excellent results (internal dipole and no ground). There are plenty of other good antennae.


If the cable is degraded you should replace it, but pulling fat cable where there was thin might be problematic. I use RG-214 myself (not LMR400 because it has a foam insulation and is sensitive to getting crushed, and is less waterproof), but you will get perfectly reasonable results with RG58. Marine VHF radios have much more power than they need (25 watts) specifically to deal with less than perfect feedlines.


With my installation (perfect feedline and good antenna) I use the radio at low power, 1 watt, 90% of the time with perfectly good results. Got a "weak but readable" signal report from the Solent Coast Guard once from -- France, 60 miles away. On 1 watt. A few extra dB lost in the feedline when transmitting at 25 watts is not going to prevent you from getting excellent results. But as S/V Illusion said -- bad connectors definitely WILL prevent you from getting even good results. I would concentrate on that.
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Old 01-10-2019, 09:15   #9
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Re: Trying to find the perfect VHF antenna

Quote:
Originally Posted by S/V Illusion View Post
It’s typically not the coax loss or the antenna which prevents effective radiated power but rather bad or corroded connectors. Or both. If the coax is old, it’s probably good to replace it too but focus on making good soldered connections on the PL259s as your most likely problem. Crimp connectors if not done perfectly and with the proper crimped will fail.

My experience is more connectors than anything else. Coax flooding comes in right behind and physical damage behind that.



Some credible sources have said there are good quality crimp connectors (NOT Shakespeare) but I haven't found any.
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Old 01-10-2019, 11:06   #10
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Re: Trying to find the perfect VHF antenna

While investigating the Vestas Wind collision during the Volvo Ocean Race, we discovered that several of the boats had terrible AIS range from their masthead antennas, and we determined that it was due to water intrusion into the foam dielectric coax cable. The antennas used BNC connectors which, while convenient, are not waterproof, and water was saturating the coax.

Use waterproof connectors, silicone grease, and shrink wrap to ensure a waterproof connection at the masthead.

Chuck
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Old 01-10-2019, 12:28   #11
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Re: Trying to find the perfect VHF antenna

Quote:
Originally Posted by Cliffhanger View Post
So, I have decided to upgrade my VHF antenna as the performance is terrible. I currently have a masthead antenna around a metre tall connected using about 18m of RG58U cable. The antenna is one of those fold-down ones with a metal hemisphere on the antenna that is clamped to a metal hemisphere in the base. A stupid arrangement that just invites corrosion and who is going to fold down an antenna at the top of a mast? I did some calcs on the RG58U cable and my 25W from the radio would be less than half by the time it gets to the antenna. Add in some corrosion on the antenna base and no wonder nobody can hear me.

So, the solution is clear, I need better coax cable, preferably LMR400 but at least RG213. I need an antenna with connections that can resist corrosion.

The trouble is that I simply can't find an antenna and/or base that will accept the thick coax i need to use.

Any suggestions?
METZ... Hands down the best and strongest. Even resisting Pelicans on the masthead. LMR 400 and coax connector seal rap.��
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Old 01-10-2019, 12:33   #12
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Re: Trying to find the perfect VHF antenna

Quote:
Originally Posted by Chuck Hawley View Post
While investigating the Vestas Wind collision during the Volvo Ocean Race, we discovered that several of the boats had terrible AIS range from their masthead antennas, and we determined that it was due to water intrusion into the foam dielectric coax cable. The antennas used BNC connectors which, while convenient, are not waterproof, and water was saturating the coax.

Use waterproof connectors, silicone grease, and shrink wrap to ensure a waterproof connection at the masthead.

Chuck

Some knowledgeable people argue with me on this, but I don't think foam dielectric coax has any place in marine VHF installations (now I do have LMR400 for my ham UHF antenna on the first spreader, but that's different).


And BNC is nuts. It's an electrically good connector, much better than UHF, but very hard to make weatherproof. I have a Type N connector at the top of the mast, encased in shrink tube and rescue tape. For many antennae you may have no choice but UHF (SO239/PL259), unfortunately, but these can be made reasonably waterproof with enough care and rescue tape


If you have a choice, Type N is the way to go.
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Old 01-10-2019, 12:47   #13
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Re: Trying to find the perfect VHF antenna

I totally agree with the advice given. I use RG-213, and will take a look at RG-214 as I hadn't heard of it before. I put my 213 into the mast in 1980 and it still works well - including the junction at the base of the mast. Still, if your RG-58 is in good condition then line-of-sight is the limiting factor, not power at the antenna.

No question that connectors are the greatest source of problems, but done right will not be an issue; so learn to do them right. That includes sealing them in a bulletproof manner. Mine are old-school: first tape over the assembled connection with Scotch vinyl electric tape, then wrap with Coax-Seal, which is a sticky putty in tape form (knead this a bit to make it one single mass), and finally wrap with a self-amalgamating tape (Rescue Tape should work well - I used the older rubber stuff). The purpose of the vinyl tape is to keep the sticky Coax-Seal from gumming up the connector, which you will likely need to access from time to time. The self-amalgamating tape is both to seal and to protect the soft Coax-Seal. Initially I used silicone electrical grease on the mating surfaces; it works great but is just too messy for me. Heat shrink is an ideal outer layer.

You haven't said what type of vessel you have. For a traditional monohull (that heels under sail) a 3dB antenna is the norm; for cats and power boats a 6dB antenna would be better. I won't buy fiberglass antennae anymore - while they are better coated than in the past, the sun does deteriorate the polyester and then the tiny glass fibers stick out - rub up against that with bare skin and you won't buy another. There are many stainless steel antennas which are incredibly durable. I'll echo the recommendation for the connector on the bottom of the antenna - no pigtails. As long as the mast is aluminum a quarter-wave base-loaded whip antenna will work fine; wood or carbon fiber will need a half-wave dipole. My current antennae are both Glomex: for VHF https://www.glomex.us/portfolio-item...rtfolioCats=80 and for AIS http://www.glomex.us/portfolio-items...glomeasy-line/ . My previous VHF was a little jewel: https://www.morad.com/products/vhf-antenna-156-deluxe . These are nicely sealed with O-rings and can be disassembled. If you buy one of these then consider covering the short plastic barrel with heat shrink; it doesn't hold up to sun over the years (perhaps they have improved the plastic in the last few decades).

You might invest in an SWR meter that covers the VHF range. This will tell you how well matched the antenna and feed are to the radio output. Test on an appropriate channel near 16 and then near AIS (87B & 88B). AIS is at the top of the band so it is possible that it is a poor match while 16 is a good match. BTW please don't test on 16 or AIS channels.

Greg
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Old 01-10-2019, 14:01   #14
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Re: Trying to find the perfect VHF antenna

Quote:
Originally Posted by Chuck Hawley View Post
While investigating the Vestas Wind collision during the Volvo Ocean Race, we discovered that several of the boats had terrible AIS range from their masthead antennas, and we determined that it was due to water intrusion into the foam dielectric coax cable. The antennas used BNC connectors which, while convenient, are not waterproof, and water was saturating the coax.

Use waterproof connectors, silicone grease, and shrink wrap to ensure a waterproof connection at the masthead.

Hi Chuck,


The big problem is that boaters, especially high end racers, think they are somehow special and unique. Best practice in commercial and military radio both ashore and afloat is much better than the garbage I see on recreational boats. This stuff isn't hard. There are so many stupid mistakes. At the top of the list are the Shakespeare crimp connectors and putting multiple antennas at the masthead. VHF for voice at the masthead and VHF AIS at the first spreader or the pushpit. This isn't hard.


Splitters are a fundamentally bad idea.



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Old 01-10-2019, 14:36   #15
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Re: Trying to find the perfect VHF antenna

Quote:
Originally Posted by Chuck Hawley View Post
While investigating the Vestas Wind collision during the Volvo Ocean Race, we discovered that several of the boats had terrible AIS range from their masthead antennas, and we determined that it was due to water intrusion into the foam dielectric coax cable. The antennas used BNC connectors which, while convenient, are not waterproof, and water was saturating the coax.

Use waterproof connectors, silicone grease, and shrink wrap to ensure a waterproof connection at the masthead.

Chuck
Shouldn't those foams be closed cell and resist water ingress? Right, maybe not for 20 years, but those boats are not that old.
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