Please critique my masthead antenna!

[Gene Neill]

This is my old antenna, which I am replacing. As you can see, the bottom 12'' do not clear above the light and the windex. How much improvement might be gained by raising the mounting arrangement somehow? If any?

I'm not eager to re-engineer the masthead, but I'm replacing the entire VHF system right now so if I'm ever going to make a change, now's the time. I could shorten the masthead light and/or move it to the other side, perhaps as much as 3" further away from the antenna?

What say you, radio gods? Worth doing or no?

 

[Timm R Oday25]

As VHF broadcast range is mostly determined by height , I'd leave it

 

[justsomeguy]

Doesn't appear all that advantageous.

How far away is the horizon?

Imagine you’re at the beach, standing on the shoreline (lucky you!). Off in the distance you see a ship on its way out to sea. Slowly it appears to get smaller and smaller, until it drops over the horizon and out of sight. How far away does the ship

blog.mathspace.co

 

[Don S/V ILLusion]

The only objective opinion can be made once you determine if there is any interaction between the two using an antenna analyzer. Absent doing that, no way to know if or how much improvement you might find by moving one.

 

[JamesG161]

if there is any interaction between the two using an antenna analyzer.

Here is a good one to use for power and testing.
https://www.amazon.com/Astatic-PDC1...hvlocphy=&hvtargid=pla-4583863993116778&psc=1
Old Ham...
Jim...

 

[Tally Ho]

Mine is certainly higher on the mast than yours…but if it works, I probably won’t worry about it.

Greg

 

[Don S/V ILLusion]

Here is a good one to use for power and testing.
https://www.amazon.com/Astatic-PDC1...hvlocphy=&hvtargid=pla-4583863993116778&psc=1
Old Ham...
Jim...

That appears to be an HF SWR meter. At minimum, he needs one which will work on VHF but I was referring to an antenna analyzer capable of measuring impedance and reactive components.

 

[dlochner]

The goal should be to optimize an antenna system to work in the waters one sails.

How far offshore will you be sailing? The USCG system can receive a 1 watt voice call from a boat 20 miles off shore.

How has the last antenna worked in its present location?

Raising the antenna a few inches may help signal propagation because the antenna will not be blocked by the mast. I have no idea how serious an issue this is, it just seems within the realm of possibility. Raising the antenna 3 inches will have little to no effect on range based on line of sight distances.

Many things affect antenna efficiency including the quality of the coax cable, quality of the soldering on the connectors, and are the connectors clean and protected from saltwater, not to mention the state of charge of the battery, lower voltage will reduce the VHF's output.

If this was my boat, I'd make sure all the connectors are clean and bright, I might replace the coax cable. I would wrap the antenna connection in self-amalgamating tape. And maybe if the screws come out move the antenna mount up a little if there is enough cable to reach the new location.

 

[BigEasy]

As VHF broadcast range is mostly determined by height , I'd leave it

This is my old antenna, which I am replacing. As you can see, the bottom 12'' do not clear above the light and the windex. I could shorten the masthead light and/or move it to the other side, perhaps as much as 3" further away from the antenna?
What say you, radio gods? Worth doing or no?

I would not be concerned about the height, your not going to significantly improve the "line of sight" VHF radio wave by increasing the height of the antenna by six inches. Since you are replacing most of the components, I would replace the antenna and cable, ensure that all connections are corrosion free, coated with anti corrosive lubricant, and ensure that they are taped & sealed against moisture incursion. I prefer soldered connectors (Amphenol) as compared to the crimp style connectors to minimize resistance & signal loss. As others have mentioned, a basic inexpensive SWR meter will confirm that your system is functioning at optimal levels. While you are working on it, I would attempt to relocate the anchor light so the antenna & light are not rubbing on each other in stormy conditions. Also, convert the anchor light to LED.

 

[Captain Larry-DH]

@Gene Neill I think your instincts are correct, as insinuated by your questions. Clearly your current setup is less than ideal. Do a web search on “interaction between antennas” and you’ll find information supporting your instinct to raise the antenna and shorten the masthead light pole, and move it away from the antenna.
There‘s a practical separation limit given the limited amount of space, and yes you do want it at the masthead. I don’t know how much (if at all) it will improve the radiating pattern, or whether the effect is measurable without sophisticated tests. I’m not pretending to be an expert on this, but I’ve done some reading.
PS - The topic of antenna coupling also comes up when people place a dedicated AIS antenna at the masthead, usually opposite the masthead VHF antenna. The question is whether they couple, and if so what’s the effect on radiating pattern.

 

[Mark Maulden]

I would relocate the antenna. The base (which is a big coil of wire to make electrically seem longer) is seemingly touching the stay tang or very very close. The tang is most likely grounded in some way or at least close to ground. This will detune the antenna affecting power, reception, and radiation pattern. The rod part of the antenna is doing the same.

 

[Apex]

forget the antenna: to all the c22> is that the correct stay terminations? I would expect swaged fittings, but don't know this model.

 

[danooxnard]

Nothing wrong with the stay connection. They are double swaged nicro presses.
As for the antenna, I would like to see the coil base higher than the top of the mast. I would not worry so much about the mast head light interfering things. I will take a picture of mine for you later today, it is a very similar situation
Dano

 

[Gene Neill]

New mounting spot. Whether or not it performs better, who knows, but I'm already sleeping better.

 

[Gene Neill]

Amazingly, the old 1980s "Sea Ranger" VHF has functioned flawlessly for the last eight years we've owned the boat. Everything is original to the boat, including these good ol' Shakespeare squeeze-on connectors.

HOW it all still worked, I don't know.

 

[dlochner]

New mounting spot. Whether or not it performs better, who knows, but I'm already sleeping better.


View attachment 214575

Sleeping better is always good. Next up for a good night's sleep is a solid anchor.

 

[jssailem]

including these good ol' Shakespeare squeeze-on connectors.
HOW it all still worked, I don't know.

Replacing that alone will improve your performance.

But to begin to address your question, you would need some serious math calculations and fancy "Antenna Radiance" test equipment. All of which likely will not make a bit of difference to the use of your VHF radio on your boat using a Shakespeare Marine Quickconnect vhf antenna.
Your Antenna radiation pattern without any reflective obstructions would look something like this.


Hide some of the antenna behind the mast and the pattern will be somewhat distorted but very functional.
Now add in the boat moving about and you can begin to understand how out at 15nm the signal may fade in and out.

Here is a good link in simple english about VHF transmissions.

How Far Will A Radio Transmit?

The Facts About Distance

www.radioddity.com

My guess is pushing the antenna up 6"s will not make much difference. Having a secure and solid place to hold the antenna is more critical than 6"s.

A couple more links for the detail oriented radio room sailor.
R-REC-BS.1195-0-199510-S!!PDF-E.pdf

Radiation Pattern

The radiation pattern of typical antennas are presented. The concept of radiation patterns are introduced, also known as antenna patterns. Isotropic, omnidirectional, and directional radiation or power patterns are described.

www.antenna-theory.com

 

[DArcy]

New mounting spot. Whether or not it performs better, who knows, but I'm already sleeping better.


View attachment 214575

You likely have improved your antenna performance by that move. All the crap up there is in the near field of the antenna and reflections in the near field can impact the performance. The other impact of stuff very close is detuning the antenna. Monopoles are fairly broad band so minor detuning won't have much effect but touching the masthead light likely would.

In general, move the antenna as far away from everything as possible and make sure the base is properly electrically grounded to the mast. Monopoles need a ground plane to form the optimal pattern you want for horizontal propagation.

Metal components should never touch the antenna element, this will have a significant effect on frequency response and impedance match of the antenna, but even dielectric materials can load the antenna and detune the frequency as well. Materials in close proximity can tune the antenna, they don't need to touch to have an effect. Poor impedance matching causes energy to reflect back along the coax cable instead of radiating out of the antenna.

 

[danooxnard]

Here are some pics of my antenna and mastlight install. This antenna coil is slightly above the mast light to allow the windex to move freely.
I like how you did yours it will work fine. Dano

 

[CarlN]

Replacing what appears to be very old RG58 coax with new RG-8X would likely help more than antenna placement. There’s a lot of signal loss using RG58 in a long run like a masthead antenna. And often some invisible corrosion after a few decades.