Help Needed for Home Made Marine Antenna

[PleasureCraft]

PLEASE EXCUSE MY USE OF TERMINOLOGY, I AM LEARNING THE CORRECT LINGO

I would like to make an antenna for my boat / marine radio. The radio is a Standard Horizon GX1700 25 Watt VHF manufactured by Yaesu. Link to the manual if needed ( https://standardhorizon.co.uk/wp-content/uploads/2019/08/GX1600_GX1700_OM_USA_EM048N161_5292013.pdf ).
I have an 18ft cruiser / power boat. I imagine creating an antenna inside a PVC pipe resembling a whip style antenna similar to what Shakespeare makes.
I have seen some plans online for Half Wave Di-Pole antennas and J-Pole. I could use advice on all aspects of the process of choosing and building the antenna.
I have an 80 or 100 ft LMR400 cable and would like to use it unless told otherwise. I also have 2 lightning arresters (I will have to check the diode or resister size in them if it matters). No other materials yet.

Thoughts and advice is needed. Plans, what style is ideal, proper lengths for the right bandwidth and DBI, materials, ect.
Just to throw out a few questions or things I have been thinking of.

1. Is it ok to put a Di-Pole antenna inside a PVC pipe folding one leg down the fully insulated wire? Or is it ideal to build it in the T position where the antenna is either horizontal or vertical?
2. I have seen a Shakespeare 5225XT taken apart on youtube (

) and the materials are interesting. There are coils toward the tip (not sure the purpose or if they're needed), brass tubes as opposed to solid or stranded copper.
3. Grounding the antenna? Ground through lightning arrester, or to radio itself?

Please feel free to lead this thread. I know I am a bit all over the place. My goal is to make an antenna that most people will agree is the best suited for my boat / radio for the Marine radio bandwidth.
If a dual band antenna for Marine Communication and AIS is possible I am open to that too. My current radio does NOT have any AIS feature but I may add it in the future.
Once I learn more I will be posting about making a GPS antenna too. I just thought I would mention it.

Thank you all in advance for your time, advice, and resources!

 

[hill]

This sounds like a bad idea for a radio used for life and safety.

I really don't know why your trying to make a homemade antenna when a commercial made one would most likely work better. Plus would most likely have better water resistance and easier to mount on your boat.

Many types of VHF-FM Marine antennas on the market and I sure you can find one and a mount that will work on you boat.

In closing with these radios being used for life and purposes it's best not to compromise on the installation. You wouldn't want it not to work when you need the USCG during an emergency.

 

[Ubbe]

All the work involved together with the risk of making a mistake makes it not worth building the antenna yourself. Marin antennas are often halfwave or 3/4 j-pole as they do not need, or should use, ground that can be difficult to find on a boat. It's VHF so no need for LMR400 that would make it more difficult to install and the stiffness could make it more prone to create a fault from vibrations. Use super flex coax.

/Ubbe

 

[PleasureCraft]

Another forum where members use ridicule against the new members. Antennas are low tech and old tech with simple assembly. Why do you assume I will make mistakes? Worth the time making?? I enjoy hobbies and making things. You think large corporations hold secrets that could never be recreated? Most home made antennas perform just as well if not better than commercial ones because the maker uses. better materials and they are not mass produced.

You both assumed I do not have an antenna to start with and give your opinion on safety. I like to build things and I have the materials.
LMR400 you say is prone to fault? It is built for reliability. You mention super flex, that is LMR400 just a slightly more flexible version and vibration won't effect either cable. My cable is LMR400UF which is ultra flex by the way.

If you do not have answers to the thread questions why comment? You both are just trying to put me and my idea down?? You do not know me and my capabilities, and you clearly don't know anything about making antennas. It is simple stuff. Yes make sure to build it correct, but the rest is just ridicule for no reason...

You say: I don't know why you would make your own antenna? Because I want to, it is that simple. All the work involved with the risk of making a mistake it is not worth building the antenna yourself. Really are you that lazy. This is easy simple work, very little room for mistakes. Measure, cut, maybe solder maybe not?? Choose the right materials... That's it..
A store bought antenna would have better water resistance? The commertial brands are known to have leaks and go cheap with water proofing. I could dip my whole antenna in polyurethane if I choose to. I have the choice to waterproof it better than any store bought antenna, and it is easy to do.

I imagine you 2 probably do not know how to use a screw driver let alone are qualified to give any advice on something technical.

Clearly I brought this to the wrong website.... Thanks for the warm welcome fellas. Goodbye. I found what I wanted elsewhere anyway.

 

[prcguy]

Large antenna companies like Shakespeare have nearly 60yrs of engineering, testing and manufacturing experience, so I would think they hold many secrets that we will never discover. They have engineers with PhDs and MS in Electrical Engineering. Antennas can be simple but they are usually way more complicated than most people imagine.

I constantly build antennas and tune/test them but I also understand that my knowledge is only the tip of an iceberg compared to actual antenna engineers. With that I would never use a home made antenna on a boat that my life might depend on.

 

[mmckenna]

Thoughts and advice is needed.

Please feel free to lead this thread. I know I am a bit all over the place.

You've been a member of this site for less than 24 hours.
You asked for the above, and a couple of people gave you what you asked for.
You are already upset and going to leave.

Fine. But keep in mind that experienced people gave you the:

time, advice, and resources!

you requested.

I get it, you didn't like the answers, but it's still good advice. You don't have to follow it, but it is your choice to be upset because you don't like it.

A store bought antenna would have better water resistance? The commertial brands are known to have leaks and go cheap with water proofing.

I doubt you are using true commercial quality antennas. Sounds more like you are using consumer grade antennas, there is a big difference, and that is what others were trying to point out. In the USCG, we didn't use hand built antennas. We used high end commercial antennas designed for the application. That's the difference between consumer/recreation/hobby antennas and commercial/professional antennas. Yes, they cost more, but that's the way most things work.

Morad Antenna

Morad marine antennas are manufactured using stainless steel and anodized aluminum materials, proven by years of field use to be the most durable alloys in harsh marine environments. Our VHF HD antennas are used by the US Coast Guard.

www.morad.com

I imagine you 2 probably do not know how to use a screw driver let alone are qualified to give any advice on something technical.

You'd imagine wrong. Both of them have a history of providing very accurate advice to others.




Yes, you can make your own antenna. Most don't since VHF marine radio is not a hobby radio service, rather it is used by many for life safety/navigation and they choose to install a quality antenna that is designed/tuned for the band by professionals. Yes, some buy cheap antennas and suffer the consequences. Others buy quality antennas and enjoy the benefits.

Making your own antenna, and one that works correctly, requires some test equipment. You can get close without it, but ideally you do want an antenna analyzer to do this correctly. One of the things you are paying for in a professionally made antenna is the test equipment to make sure it works correctly. If you have your own test equipment, great. If you don't, you probably want to get the appropriate equipment. It won't be cheap, and may end up costing more than a commercial (not consumer) quality antenna. Your choice and we fully understand the challenge of building it yourself.


You can build a simple sleeve dipole by pulling the outer shield back down the cable. It's not going to be a high performance antenna, but it'll work. Do some searching on "sleeve dipole" to get some ideas. You need to find a way to keep it straight in the PVC pipe and not allow it to compact/slouch inside the tube. Filling the PVC pipe with something to hold in in place would be a wise idea. Make sure it's something flexible so the antenna can flex. You don't want it so still it breaks.

That's about as simple as you can go with a home built antenna like this. If you want something that is going to work better, you need to phase multiple elements together. That is a challenge since you are working with RF and not DC, so your multimeter isn't going to do you a whole lot of good. You'll need to roll your own phasing coils to make this work.

J-Poles are a simple antenna and provide no gain. Their benefit is that they are easy to build. It isn't going to magically work better than anything else.

You can build ground plane antennas, but then you have to deal with the ground plane. That isn't a good choice on a boat as you'll need some metal under the antenna. That usually means the antenna is mounted on a flat surface. That works against you since VHF tends to be line of sight in most cases, and for best performance you want the antenna up as high as you can get it.

In fact, if you want your antenna to work better than all others, the best thing you can do it get it up as high as you can. That'll make a lot of difference.

You want the antenna and its internal elements to be vertically oriented. Everyone you'd want to hear/talk to is going to be running vertically oriented antennas. Running yours horizontally will result in a considerable amount of signal loss.

LMR-400UF might work fine, but for VHF use on a small craft like that, the size is overkill. Usually the larger coaxial cable is used where signal loss over a long length is a concern. Your boat isn't big enough for that to be a concern. Yes, you can use it, but you may find it easier to work with something smaller. You also need to consider the connectors and their installation. Easier to do on smaller cable, harder on larger stuff.

Lightning suppressors on a boat your size are not necessary. As others pointed out, simply grounding it to the engine block isn't going to do you any favors. If lightning finds your boat, a damaged antenna/radio is going to be the least of your challenges. I've been on ships that have been hit by lightning and trust me, you have bigger things to worry about. A lightning suppressor isn't going to shield your radio from lightning, it's just going to help some of that energy go somewhere else. Your radio is still going to get destroyed.

You can find calculators on line that will help you figure out antenna element lengths, but you'll still need to do some testing once it is built. There are variables in coaxial cable that need to be considered and that will play into the design.

As for AIS, you don't need a dual band antenna. AIS runs on two of the top VHF channels and radios that have built in AIS capability just use the same antenna as the voice part of the radio. No need for a separate antenna, unless you are running a stand alone AIS transceiver. A properly designed/built VHF marine antenna is all you need for voice and AIS.

 

[TrainsOfThought]

In closing with these radios being used for life and purposes it's best not to compromise on the installation. You wouldn't want it not to work when you need the USCG during an emergency.

As a past boat owner, it's quite common here on the Chesapeake Bay to encounter a Coast Guard on-the-water boat inspections for safety etc. Akin to being pulled over for a highway truck inspection, I doubt a home-made jury-rigged marine antenna would pass muster considering the enormous weight placed on them for emergency or disabled situations. Home-made antennas are just a non-entity out on the water and community. Best advice given (seemingly ignored) and considering the money-pits boat can become is NOT to go cheap on an emergency communication antenna...purchase a name-brand antenna. You'll never regret it. IF you want to play or experiment with a home-made, do it on shore in the shop and from shore but I'd never rely on it for my, family or passenger's life (in case of emergency or accident on the water, that home made could become a HUGE liability insurance nightmare).

 

[laidback]

Youtube video :

 

[JustinWHT]

You can certainly build your own antenna providing you understand critical nuances and have adequate test equipment. I'll start with the nuances - white irrigation PVC can detune an antenna, more so with outdoor electrical conduit PVC; for test equipment a Bird watt meter and sweep analyzer are necessary.

PVC tubing has poor mechanical fatigue when you have a twenty foot length whipping around, and white irrigation pipe without painting will self-destruct after several months in summer sun. The original twenty foot VHF fiberglass antennas were painted - the white paint on a Phelps-Dodge "Station Master" antenna will eventually degrade and raw fiberglass all over (a helper pulled one loose and let it slide down his gloves against his chest), other than installing one Decibel Antennas "DB356" blue-dyed epoxy coating I have no idea how long they last. That was all from the mid-'70s experiences.

Now as for calculation antenna gain. The J-pole that is functionally a dipole antenna where the gain is unity or 0 dBd gain compared to a simple dipole or 2.14 dBi expressed as an isotropic antenna. In gain antennas we consider each dipole and associated spacing from next vertically aligned element as a "bay"; thus a four-bay DB224 VHF antenna would have 6 dBd over a simple half-wave vertical dipole or quarter-wave mobile mobile ground plane antenna (both unity gain). Therefore a 6 dBd gain antenna may it be four stacked vertical dipoles or four stacked co-linear elements in a fiberglass antenna would both be around twenty feet long.

As for home-made antennas preforming better than $1,500 commercially built antennas ... hogwash.

I've built co-linear antennas with PVC covers using RG-8 and 1/2" foam-core Heliax (tm Andrews Corporation) ... but then I have a $6,000 Anritsu coax and antenna analyzer.