Masthead Antenna Installation Help

[jdratlif]

I recently purchased an O'day 25. I have started getting things in order to do the spring maintenance I want to complete before I put her in for the season. The boat has a VHF radio and is wired with a mast head antenna. I recently looked at the mast head antenna and it looks like something is missing and that the installation job was not done that well. I have attached photos of what I have installed on my mast head where the antenna should be. My questions are, what is missing from this and what would I need to do to get this antenna functional? I have never installed a VHF antenna before so I am not sure what I am looking at. I have researched on the web but I cannot find any good sites for masthead antenna installations.

Thaks for the help

 

[DannyS]

Not to state the obvious, but...

You seem to be missing the antenna.

 

[Joe]

When you buy an antenna... there will be instructions.... you already have a bracket...the rest is easy, unless you want to run the cable inside the mast, then you'll have to drill a couple of holes.

 

[Roger Long]

Did you see the Coax thread?

http://forums.sbo.sailboatowners.com/showthread.php?t=126879&#post789694

I didn't know any of this so I hand soldered my connectors using (I can't remember what but it was the better grade available at the marine supply store). Two years later and performance is quite good. I'm not sure what I would do if I were redoing it after reading this; probably obsess and go overboard as I tend to do on other things. If water is coming in and you are yelling for help just before getting in the dinghy or life raft, another few miles of range and signal clarity could be important.

A agree with the poster in the thread who says antenna height trumps power though. I used to fly an airplane with two different radios. One was 25 watts and one was 10. I never noticed any difference in range. If anything, the 10 watt radio was better and I mostly used it.

Since your mast is down, I would certainly try to run new coax and connectors though. It's cheap insurance. That taping job doesn't inspire much confidence.

 

[kpgraci]

I might add - do not attempt to transmit on the radio without a proper antenna hooked up - that power needs somewhere to go and the radio may get fried.

 

[Barnacle Bill]

You are pretty much missing the whole antenna. Looks like you have the PL259 at the end of the coax coming out of the mast, and you have the PL258 between it and the other PL259 (all under the black tape), but above that you have remnants of what was once an antenna. You, you are going to have to fork out around $70 for either a Metz whip antenna or a Shakespeare whip antenna designed for sailboats. (My choices). Shakespeare also has a racing whip antenna that is smaller, but either is a good choice.

 

[Skip Gundlach]

It looks to me like you have a 1x14 screw-on mount, and, perhaps, some old coax that was loaded up with tape (to protect it??).

Others have chimed in about running cable inside the mast - I went through a new cable installation to improve mine, and it comes out the top of the mast, then does a large loop up and then back down and up to my antenna, which I moved out on a bracket (my WiFi setup is on the other side, the better for both of them to be isolated from as much metal as possible for best performance).

So, as it's not a lot of money (about a buck a foot, if I recall correctly), I'd do the waterproof stuff, LMR400, if my memory serves me properly. If you're really worried about performance, you can get the milspec kind of cable, different flavors to suit your preference (lowest loss, most water impermeability, etc.).

But with that base, you'd have to get one of the ones which will screw on to the 1x14. My aft antenna, on the arch, is one such. However, the mast-top one is a metz coil with a standard VHF connector, previously mounted on a thin plate, right at the top of the mast. That (no bracket distance as I have now) resulted in a very sharp turn up, down, up, to connect to the stem of the antenna.

If you do run it in the mast, be sure to support it at the top so it's not trying to pull through whatever sort of gland you use (mine's a hole in the top of the mast, and a fair amount of 101 (did you know that 3M no longer makes that stuff?!?)...

HTH

L8R

Skip


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[Forrest15112]

You obviously need to replace the antenna. For best performance, get it as high as you can and mostly above the top of the mast. Another thing not usually mentioned is antenna gain. Different antenna designs will have an improvement over some theoretical design or a dipole. They may indicate gain as dB, dBi, or dBd. Most will use dBi and printit only as dB, which is correct but doesn't tell the whole story. The higher the gain the better the signal, right? Well, you might think so, but not in all situations. The antenna, by design, doesn't amplify or increase the signal. It just redirects the energy. That theoretical antenna that most are compared to is an isotropic radiator. Picture a radio signal field that emits equally in all directions - like the Sun. If you could take the energy that is being sent down towards the ground and focus it into the other directions, you get a radiation pattern that resembles a light bulb, but a little brighter than before. Various omni-directional antennas simply flatten that signal out more and more to something shaped like a disc ( horizontally). Less energy to the top and bottom, so more goes out the sides. All is still good if it gives you more range but in the case of a masthead installation, the antenna will not be vertical while heeling and a high gain (6dB or more) antenna will have the majority of the energy focused at the sky and the water. For this reason, you would want to stick with a simple 3dB(i) gain whip which will have that light bulb radiation pattern and perform well even heeling over at 30 degrees. You will see some antennas rated for 5dB gain which is OK but above that and you could lose some performance.
This is especially true on the power boats you see with the big high gain antennas that they angle back because it looks good.