VHF ANTENNA CONNECTION

[Globalhobo]

Aloha,

We are slowly working on our 26M that we got last year (finishing the house took priority, so she has been sitting). Being the first trailer sailer we've owned, we're wondering: What do you guys use for through the deck cable to your vhf? Raising and lowering the mast seems like maybe a connector similar to the connection to the mast head lights would be good but we can't seem to find any.

Thanks!
Leah

[dlandersson]

I have a BNC connection (sold by WM) that is located right by the base of the mast. You disconnect it before raising or lowering the mast.

Aloha,

We are slowly working on our 26M that we got last year (finishing the house took priority, so she has been sitting). Being the first trailer sailer we've owned, we're wondering: What do you guys use for through the deck cable to your vhf? Raising and lowering the mast seems like maybe a connector similar to the connection to the mast head lights would be good but we can't seem to find any.

Thanks!
Leah

[NiceAft]

My VHF is rail mounted. It has served well for many years.

Ray

[Tomfoolery]

You can buy deck fittings for PL-259 connectors, like this . . .



. . . or you can use a deck fitting with a rubber gland to bring a short length of coax out . . .



. . . or you can use a tiny clamshell fitting to bring the cable out, which the PO did with my boat. A short length of RG-8 to a PL-259, with a similar PL-259 connector on the coax out of the mast, connected with a double PL-258 connector.

I also have a ratchet mount for my 3dB whip on top of the mast that the PO installed, like the one NiceAft posted above, and while hardly necessary, it sure is nice to be able to fold it back against the mast when I tarp the boat.

[Highlander]

Mine is mounted on top of my arch , that fiberglass one has since been replace by a 3-4ft s/s one


U can barely see the S/S antenna it just above my head


J

[Highlander]

Ray
U need to do something with that wire it is badly exposed should have entered the deck right beside the base !

Just sayin thats all

J

[NiceAft]

Thanks John.

That's the way the dealer installed it in 2004. Its been that way ever since. Another hole I may have to drill in the boat.

Ray

[March]

We have an antenna on the port side, for local sailing. It works pretty well. But when we sailed to the Bahamas, we added a cable through the mast and mounted the antenna next to the Tacktick wind sensor. It expanded the receiving area, by something like 15 NM (or so they say)
The biggest problem was guiding the cable through the double lining, inside. The plug is just behind the mast, out of the way, but you might want to consider it mounting on the side, opposite to the other plug for the mast lights. The hatch hits it, if we're not careful

[yukonbob]

Mine is mounted on top of my arch

I'll second this install. The fewer the connections from antenna to vhf the better signal and less chance of damage or dislodging. We have a 5 or 6 ft whip off the arch and we get 7-10nm signal in narrow fjords of Upper Lynn canal, less on miserable days.

[Tomfoolery]

It expanded the receiving area, by something like 15 NM (or so they say)

The 'radio horizon' for VHF, which is mostly line-of-sight, can be estimated as d=1.22 x sqrt height (above the water, in feet). That's taking into account the small amount the radio waves will 'bend' over the surface.

Using the middle of a 3 ft (3 dB) whip on top of an mast, which is 5 ft (hull) + 28 ft (mast) + 1.5 ft (halfway up the antenna) = 34.5 ft. So d = 1.22 * sqrt(34.5) = 7.2 nm.

Mounting a 6 ft whip on the rail with an h of about 7 ft (4 ft to the rail plus 3 ft to the center of the whip) yields 3.2 nm range.

But range also depends on the other guy's antenna, so another boat with the same 3 ft whip on the same size mast would give an effective range of around 14.4 nm. A 100 ft USCG antenna tower would be able to reach out something like 12.2 nm, plus the range of the boat's antenna (to the horizon), so you get something like 19.4 nm.

That's theoretical, of course, but it highlights how much the range improves with height when the height off the water is small, but as it gets up there, range doesn't increase that much.

[Russ]

The 'radio horizon' for VHF, which is mostly line-of-sight, can be estimated as d=1.22 x sqrt height (above the water, in feet). That's taking into account the small amount the radio waves will 'bend' over the surface.

Using the middle of a 3 ft (3 dB) whip on top of an mast, which is 5 ft (hull) + 28 ft (mast) + 1.5 ft (halfway up the antenna) = 34.5 ft. So d = 1.22 * sqrt(34.5) = 7.2 nm.

Mounting a 6 ft whip on the rail with an h of about 7 ft (4 ft to the rail plus 3 ft to the center of the whip) yields 3.2 nm range.

Thanks for doing the math Tom.
Why I prefer mast top antenna. Plus, it's out of the way. Coast Guard towers are on tall towers for the same reason. Some have mentioned demasting as a reason to deck mount. So why not both, or keep an emergency antenna or hand held.

Mine is just the PL259 barrel with lots of glue around it.



http://www.amazon.com/SHAKESPEARE-ELECT ... 259+barrel

--Russ

[yukonbob]

Yes waterproof handhelds are a must.

[Tomfoolery]

The 'radio horizon' for VHF, which is mostly line-of-sight, can be estimated as d=1.22 x sqrt height (above the water, in feet). That's taking into account the small amount the radio waves will 'bend' over the surface.

Using the middle of a 3 ft (3 dB) whip on top of an mast, which is 5 ft (hull) + 28 ft (mast) + 1.5 ft (halfway up the antenna) = 34.5 ft. So d = 1.22 * sqrt(34.5) = 7.2 nm.

Mounting a 6 ft whip on the rail with an h of about 7 ft (4 ft to the rail plus 3 ft to the center of the whip) yields 3.2 nm range.

Thanks for doing the math Tom.
Why I prefer mast top antenna. Plus, it's out of the way. Coast Guard towers are on tall towers for the same reason. Some have mentioned demasting as a reason to deck mount. So why not both, or keep an emergency antenna or hand held.

Mine is just the PL259 barrel with lots of glue around it.

That's why I have both an emergency antenna that my FIL gave me, stored in the plastic tube it came in. And I also have a waterproof handheld, which I use 99% of the time, since I'm rarely very far from anyone I need to speak with. http://www.gandermountain.com/modperl/p ... gQod3fEIvQ

I also carry another VHF radio, identical to the older unit that's installed in teh boat, which I already had laying around, so I store it on the boat. It's gotta be stored somewhere; might as well store it where it can do some good on the off-chance it's needed.

[Globalhobo]

Wow, thanks for all the input! We were looking at the deck mounted fitting to keep it "clean", watertight and not have too much hassle disconnecting when lowering the mast. We had planned to do a mast antenna and once I wrap my head around Tom's equation , maybe we can switch to the arch mounted one. Someone on the facebook Mac page had said they got a combo wind indicator/antenna...we liked that idea too.

[Tomfoolery]

Wow, thanks for all the input! We were looking at the deck mounted fitting to keep it "clean", watertight and not have too much hassle disconnecting when lowering the mast. We had planned to do a mast antenna and once I wrap my head around Tom's equation , maybe we can switch to the arch mounted one. Someone on the facebook Mac page had said they got a combo wind indicator/antenna...we liked that idea too.

Davis Windex AV. $50 at West Marine.



It's bigger than the Windex 10 (sport) I use on the mast, but it makes for a clean installation as it mounts right on the whip.

The small SS whips have 3dB of gain, and the big fiberglass units have 6dB of gain (twice the power at a point some distance away). The higher gain is due to a narrower elevation aperture, so the apparent power received from (or transmitted to) some point at a fixed distance is twice as high for the 6dB over the 3dB, but the power drops off with the antenna tilted faster with the 6dB than with the 3dB. The effective vertical beam width is narrow on the 6dB, in other words, and wider on the 3dB, which makes sense of course, as the antenna has no power of its own, and the gain has to come from somewhere.

So it's like a donut laying flat - the 3dB is a fat one with small radius outward (perp. to the whip), and the 6dB is a thin donut, but extends farther out. Or maybe a lighthouse with narrow and wide vertical focus, but the same light bulb 'brightness' (power from the radio when broadcasting, in this case) - light looks brighter at some distance with the narrower focus, but tilting the lighthouse makes the intensity received less bright at smaller angles of tilt than with the wider vertical beamwidth, which give less brightness, but at wider angles of tilt.

That's why powerboaters mostly use 6dB whips; their boats don't heel, and they're close to the water, so the transmit and received signals are better served by squishing the pattern, resulting in it extending farther out. The half-power beam elevation is narrower (angle above and below a disc perpendicular to the whip at which gain is one half of max), so the apparent power at a distance is higher than a 3dB, but drops off quicker within a narrow elevation band. Sailboats, on the other hand, heel, so widening the beam elevation (up and down) to compensate for the whip not being vertical is the ideal.

I honestly don't know if the lower gain and wider beam elevation of the small whips is better on a heeled sailboat than the higher gain and narrower beam elevation of the big ones, but I'd guess it is, as heeling at 30 degrees is likely to put the horizon almost into a null, where the gain drops into the negative region, making the antenna useless. And since you really don't want an 8 ft fiberglass antenna on top of a mast (or a 20 ft 9dB ), I guess it all works out for the better to use the little one.

Plus, you can mount a Windex on it.