VHF options for trailer sailor

Stu Jackson · Apr 20, 2009

48dodge said:
What's everyone else done?

Something different!

You almost answered your own question, in terms of range required.

We have a down below masthead antenna fixed mount, but hardly ever use it. Handheld in the cockpit used 99% of the time.

Choices are obvious: down below only, our setup, remote wired or wireless mic in cockpit from main station down below. Your boat, your choice.

Stu Jackson · Apr 20, 2009

OK, now we understand

If your mast is down, why not go higher, better signal and if you're out and about on larger water, you'd get a better signal.

If the mast is up, then go with the pushpit mount and see how it works, you can always do the mast mount later.

That's what I'd do if it was my boat, and I used to have a trailer sailed C22, so understand your issues.

sailingdog · Apr 20, 2009

I would mount the antenna on the masthead. It will greatly increase your range. You can terminate the antenna cable with a PL-259 fitting and use female-to-female coupler to pass the VHF connection through the deck.

Photo courtesy of binnacle.com, click to see product there.

Rick Webb · Apr 20, 2009

Difference in Range

With the anntenna on the rail at at nine feet high you'll get your signal out about 3.6 miles. On top of the mast at 36 feet up you'll go out 10.8 miles.

How far away do you want to talk on the radio?

sailingdog · Apr 20, 2009

If you have an emergency... there are a lot more guys listening in s a circle 10.8 miles in radius than there are in one 3.6 miles in radius.

Rick Webb said:
With the anntenna on the rail at at nine feet high you'll get your signal out about 3.6 miles. On top of the mast at 36 feet up you'll go out 10.8 miles.

How far away do you want to talk on the radio?

Bill Roosa · Apr 20, 2009

Line losses

VHF frequencies are very bad for line losses in the antenna feed line. I've seen mast mounted antennas that don't transmit as far as a handheld with a rubber duck antenna due to using coax that is not up to snuff. Be sure to use the right coax (more expensive and larger in diameter) to get up the mast. The 259 connector (I think that is the right number) interfaces with the right 50 ohm impedance coax for max signal strength. Definitely do not go with the smaller diameter coax as even 30' of it can give 3 dB loss (8 times less) in signal. Avoid coiling the excess feed line as that creates an electrical device called a choke (inductance) that will seriously attenuate the signal going out. This applies to GPS antennas feed lines too BTW.
Also if you have a demasting you will be SOL for using your VHF if your antenna is on the mast.

I'd recommend a shorter run of high quality coax mounted on the stern rail as the best compromise. Also consider using a medium gain antenna to get more signal out.

Not sure where Mr. Webb got his numbers but at 9' above the water I get (from Bowditch) the distance to the visible horizon to be 3.5 nm. VHF travels about 1/3 farther due to diffraction or 4.6 nm. You then have to add the other antenna height to get the actual range. Most USCG have 150' antennas so adding 14.3 nm for a visual range and adjusting for VHF I get a 9' antenna talking to a 150' antenna to be 4.6 + 19.1 = 20.7 nm and for a 9' antenna talking to a 50' antenna (another sailboat??) I get 14.9 nm.

Don S/V ILLusion · Apr 20, 2009

Just to amplify what Bill said above, here are some comparisons of attenuation figures at 150 MHz of good quality coax typically used on boats:

Type - - - db loss/100 ft

RG213 -------------- 2.8
RG58 ------------------6.8
RG8 --------------------1.8 (CXP138FX cable - not generic RG8
RG8x mini ------------4.7

As you can see, the widest disparity is 5 dB which is significant in that the loss is over 50% of your power so if you want to install the antenna as high as practical, the trade-off may not be worth it depending on the quality of the feedline.

Since this specific type RG8 is not commonly found, I'd recommend anyone use only RG213 regardless of antenna location as the difference in price between it and the cheap stuff is minimal.

Rick Webb · Apr 20, 2009

Numbers I used

I used 1.2 rather than 1.17 as it was easier to multiply in my head.

The point was to illustrate the difference in range between a rail mounted antennae and one on the mast. A tenth of a mile does not change things much.

Timo42 · Apr 20, 2009

I mounted the antenna on a bracket almost at the top of the mast on the port side, masthead light at top and windex on a bracket off to the other side. I remove the windex and antenna when trailering, I have a feedthrough in the deck at the base of the mast like the one in Sailingdog's pic. The picture is of the bracket and cable, you can see the windex bracket on the other side. The bracket is low enough for the antenna coil not to shield the light.

Joe11688 · Apr 20, 2009

48dodge said:
I'm 99% done rewiring my boat right now. Getting ready to put the new hull liner on soon. Anyway, I wanted to figure out if I want or need to wire up an antenna on the mast for my VHF. Or should I stick with a deck mount option. What's everyone else done? I don't need the signal to reach halfway around the world, mainly just around the charleston harbor and surrounding areas.

Dodge,
If you have a Z-Spar mast with internal halyards, you could run your coax up through the mast with no problem at all. The best way to do this is to disconnect the anchor light and remove the mast head fitting. Then remove the Tabernacle from the mast and tie a string to the duplex light wire and pull the wire out from the top of mast. The wire is probably going through a strap near the top of the mast, and you can leave it like it is and try to get the rest of the duplex cable out of the mast. When you get it all out, just tape the coax to the duplex wire about ever 12" and pull both wires back into the mast. All you need is a Shakespeare Stubby antenna which comes with a bracket that can be screwed to the side of the mast, some connectors, and a thru-hull coax connector. I bought my thru-hull coax connector at C E Beckman in New Bedford Ma., years ago. I also bought a screw on cap for it to keep the water out when the coax isn't plugged in during lay up periods.

Joe11688 · Apr 20, 2009

48dodge said:
I'm guessing the top of the mast is the only option for mounting on the mast. I just mounted my windex up there but I could definitely move that if I need to. Since my 222 is a fractional rig, any chance I could mount the antenna on the front of the mast just above the headsail? Or would the antenna block/absorb too much of the antenna signal?

Dodge,
All you'll need for your windex is a 12 inch extension bracket so that it doesn't interfere with your antenna. I don't even think that you'll need to drill any holes in your mast for the coax on either end. You'll need to drill and tap for the machine screws that hold your brackets, and that's about it.
Joe

pmitch · Apr 21, 2009

Could you be a little more clear with what a "Stubby" is...and the related equipment req'd

sailingdog · Apr 21, 2009

For a sailboat, I'd go with a 3 dB gain antenna, like the Shakespeare shown above or the Metz equivalent. The higher gain antennas aren't as useful on a sailboat, since they have a much narrower vertical angle of coverage...and don't work as well when you're heeled.

Bill Roosa · Apr 21, 2009

Antenna gain and range

Good point sailingdog but you have to look at the vertical radiation pattern for each antenna to actually tell. Yes a higher gain antenna does concentrate the signal more toward the horizon (when vertical) but all vertical whip antennas radiate upwards to begin with so a higher gain may in fact radiate better to one side when heeled. Most are familiar with the horizontal radiation pattern of a vertical antenna being a circle. But the vertical radiation pattern is a bent figure 8 on its side with the edges of the 8 just touching the horizontal line (0 heel angle). The best radiation strength is usually at 10ish degrees up from the horizontal for both.
My personal opinion is that I'm going to be talking to the place that I'm going to and that would be forward. The heel angle does not matter in that (or the stern) direction.
Also you want 1:1 SWR. A 1.5:1 is not that great and using the right 50 ohm (48dodge's case and it is typical) coax is the way to lower the SWR for max power transmission to the antenna.

Rick
my point was that the height of the antenna is not the only factor in range. If you suffer line losses getting the antenna up the mast it is a moot point as far as range is concerned. There is also the maintenance issue to consider.
To recap:
Higher is better
lower line loss is better (and increases with feed line length aka height)
Demasting renders all your mast mounted antennas inop
Clean tight connections are better and we are operating in a marine environment.

VHF options for trailer sailor

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