VHF Antenna on a wooden mast

[johngsandusky]

I want to install an antenna aloft on my mizzenmast. I'm worried about adding holes to the stick by screwing directly to it. I thought I'd glue a block onto the mast, then screw the antenna to that. Anyone tried it?

[Vinny&Shawn]

I don't think gluing a block to the mast is a bad idea, but maybe unnecessary all of my mizzens carried the antenna on a mounting bracket screwed and properly bedded directly to the mast below the truck. Never had a problem. I not sure if the momentum of the antenna whipping about would weaken the glue block and actually you have to make a block fitted to the mast to get around the truck. So you need to put screws through the bracket and block and into the mast for strength.

[rbgarr]

If your mast is solid there shouldn't be a problem, but a box section/hollow spar can present some. They can leak and end up holding water:

A local Concordia yawl's boom leaked through the track fastenings and took a long time to dry out before repairing. Belle Aventure, a big Fife ketch, had the mast pulled for a yard period here and they found that the bottom quarter of the mast was full of water.

[paladin]

If you can get inside the mast for the coaxial cable, you don't need the antenna, just peel back the black covering on the coax, carefully, for 21 inches, exposing the braid. Then using your pointy marlinspike or the point of an icepick, carefully work to loosen the braid where the black part ends, and fish the opaque center conductor through the braid without breaking it. Straighten the opaque part, straight up for 17-19 inches, and turn the braid downward and tied it with the black part of the coax....then slip a large piece of heat shrink over the entire think and heat it with the missus hair dryer....VOILA instant antenna that I betcha works as well as the umpty ten fourty sawbuck one....epoxy it in place inside the spar.....UH....This only works with WOOD spars......

[johngsandusky]

The masts are wooden, rectangular, and presumably hollow. But I'm not pulling one for this project. I'd put it on a spreader, but the mizzen doesn't have them. Maybe the main spreader is the place.

[paladin]

If you mount the antenna on a spreader then the antenna must be of the 5/8ths wave or 1/2 wave type, as there is no metal on the spar for the counterpoise (called a ground by folks that dunno no better)...it's not really a "ground" as the antenna must see an electrical representation of itself to function properly.

[Captain Blight]

If you can get inside the mast for the coaxial cable, you don't need the antenna, just peel back the black covering on the coax, carefully, for 21 inches, exposing the braid. Then using your pointy marlinspike or the point of an icepick, carefully work to loosen the braid where the black part ends, and fish the opaque center conductor through the braid without breaking it. Straighten the opaque part, straight up for 17-19 inches, and turn the braid downward and tied it with the black part of the coax....then slip a large piece of heat shrink over the entire think and heat it with the missus hair dryer....VOILA instant antenna that I betcha works as well as the umpty ten fourty sawbuck one....epoxy it in place inside the spar.....UH....This only works with WOOD spars......Sorry, Chuck, I can't brain today because I have the dumb. I'm gonna need to see a photo or something because I'm just not gettin' it.

[paladin]

Well DARN! I made you a pretty little drawing then went to save it as a jpeg file to load it and I somehow managed to erase it totally......yure gonna have to wait another day cause I just took my dope and gonna go nap time.....
Braid of cable, 19 inches pulled back over cable
........................XXXXXXXXXXXXxxxxxxxxxxxxxx xxxxxxxxxxxxxxx
Center wire of cable main cable
19 inches long

when finished, pull a piece of shrink tubing over the entire mess an shrink it to keep moisture from wicking into the cable...

I know...bad piktoor....

[Gezzunder]

Back to basics :)

Electrickery, put simply, is made by magnets. Pass a magnetic field across a piece of wire and it will push electrons in the metal one way or the other.

This movement of electrons is electricity. The faster the movement, the higher the voltage - no movement = no voltage. The strength of the movement is measured as current. If the movement is all in one direction, we call it DC (direct current), if it swaps direction we call it AC (alternating current).

The number of times a second that the electrons swap direction is called frequency (makes sense doesn't it?) and the length of time it takes for the voltage to build from zero volts to peak voltage and back to zero volts is called the wavelength. VHF marine radio has a wavelength of around 2 meters (six feet for you imperialists :)

Finally, if AC is applied to a wire, the movement of electrons back and forth generate a magnetic field. The stronger the current in the wire, the stronger the magnetic field and the further that field can travel.

So if we get a piece of wire some distance away from the first piece, we can actually see the effect of that magnetic field as it induces a similar voltage into our second piece of wire. RADIO!!!

Now the electrons in our recieving wire need to travel. For them to do work they have to reach our radio. As they travel in one direction they reach the radio which is good. In the other direction, they reach the end of the wire - not good. Not a problem, they bounce of the end of the wire and head back the other way down to the radio..... sweet. What happens though if they bump into electrons heading the wrong way? They all slow down (kinda like cars in a headon). So what we need to do is make sure the wire is the same length as the waveform, this way as the electrons hit the end of the wire and bounce back - all the electrons are changing direction anyway.

For this reason, antennas are cut to a set length according to the wavelength of the frequency they are designed to recieve. Rather than sail around with whopping 2 meter long antennas, we cut them to half, quarter or some other even fraction to reduce the effect of electron head-ons.

Now the amount of actual voltage recieved by your antenna is two fifths of five eights of bugger-all. The job of the radio transciever is to amplify that pitiful voltage so we can use it. As you can imagine, there's more than one magnetic field out there and we need to get another piece of wire from our radio to the antenna without also recieving all the other transmissions. To do this, we wrap that in yet another piece of wire so it can intercept those transmissions instead. They thought long and hard about it and called this the "shield".

Coaxial cable is a center conductive wire, with a shield wrapped around it.

Paladin's suggestion is to remove the shield so as to allow that center wire to act as an antenna. The length's he's quoting would be set to match the wavelength. I work in metric so I can't confirm that, but I'm gonna assume that Paladin is an allright guy and has done the math :)

Having said all this (phew!) I reckon that commercially made antennas will have a few more tricks up their sleeves and will almost certainly work better than our simple coaxial jobby, but then they look ugly on a pretty yacht - especially if we're aiming for a classical look.

If you're priority is to get maximum range from your radio.. go commercial and put it as high as you can so it can see further. I like the cleverness of having a concealed antenna I made myself.

[Iceboy]

"the length of time it takes for the voltage to build from zero volts to peak voltage and back to zero volts is called the wavelength. "

Sounds like a half wavelength to me. Unless of course things have changed in the southern hemisphere since I was there last. Gotta have swing on both sides of zero to make a wave.

[paladin]

Just like car accidents a small percentage of collisions on a supehighway where we have millions of elektrons ain't agonna amount to a hill of beans....we can have tons of collisions (called SWR (standing wave ratio) due to mismatched antennas and it will only effect 2-3 % of the power......

[Gezzunder]

"the length of time it takes for the voltage to build from zero volts to peak voltage and back to zero volts is called the wavelength. "

Sounds like a half wavelength to me. Unless of course things have changed in the southern hemisphere since I was there last. Gotta have swing on both sides of zero to make a wave.

Doah! This is why my instructor's used to nail me... make it too simple and miss simple stuff.:o

[dredbob]

Having said all this (phew!) I reckon that commercially made antennas will have a few more tricks up their sleeves and will almost certainly work better than our simple coaxial jobby, but then they look ugly on a pretty yacht - especially if we're aiming for a classical look.

No, on this you are wrong. A homemade antenna of the correct length and configuration will work exactly as well as a similar commercially made antenna. The commercial antenna may (or may not) be more robust than the homemade one, but an antenna is an antenna and electrons and radio waves don't make any distinction between the two.

Chuck's description is of what we call a "coaxial dipole" and it will work just fine. Do a google search on that and you'll find plenty of instructions for making them. Another similar antenna that can be easily constructed is a "twinlead J-pole". Look that one up too.

Either of these make very effective VHF antennas, and even if you already have a masthead mounted antenna, these are great backups, that can be coiled away until needed.

A little trick that I like for these kinds of antennas for traditional boats is to cover it with the outer braid of a piece of buff colored double braid. Take a length of the line long enough to cover the antenna and the feed line from aloft to where ever. Attach the end of the antenna to the center braid (or filaments or whatever) and pull the center braid out from the other end, causing the antenna/feed-line to be drawn in. Sew and/or seize an eye in the top end, being sure to capture the top end of the antenna element securely inside, and now you have a flexible antenna/feed-line that looks like the rest of your rigging.
Remember that these must be kept away from metal rigging and spars, but will be perfectly happy hoisted alongside a wooden mast, or up to some point on a topping lift, etc.

---
Bob

[Captain Intrepid]

If I'm not mistaken a fathom of any kind of antennae material will work as an emergency channel 16 antennae.

[JimConlin]

Chuck, will that work inside a carbon mast?

[Gezzunder]

.

No, on this you are wrong. A homemade antenna of the correct length and configuration will work exactly as well as a similar commercially made antenna. The commercial antenna may (or may not) be more robust than the homemade one, but an antenna is an antenna and electrons and radio waves don't make any distinction between the two.

You are correct.

If, however, John decides to purchase a multi element jobby which has a flattened radiation pattern then he will find his transmissions received by ships further away than you and your dipole with it's spherical pattern.

There's a whole lot more to it than just blatting out of the stick.

[paladin]

Carbon is metal.....don't hide your antenna inside a metal tube...no aluminum, no carbon,.... fiberglas or wood only....

[Gezzunder]

Back to the original question though, what about using banding or strapping to secure the antenna to the top of the mast?

[Vinny&Shawn]

Which antenna are about to use,the home made or the commercial? If the commercial one comes with a bracket, make a mounting block and screw it to the top of the mizzen. Proper bedding and maintenance will prevent water intrusion, even if the mast is hollow. Most times in hollow spars there are backing blocks built into the interior to except fasteners for designed add ons,check these areas. You can sound this out with a light hammer,wood, plastic,rubber.
I think banding or strapping is OK.but you must protect the mast with blocks or wedges, leather other padding of your choice. Look at other examples. In this case you still have to worry about fresh water getting in behind. Simple is always kinder to the wood.

Do you have pictures of your mizzen?

[dredbob]

You are correct.

If, however, John decides to purchase a multi element jobby which has a flattened radiation pattern then he will find his transmissions received by ships further away than you and your dipole with it's spherical pattern.

There's a whole lot more to it than just blatting out of the stick.


Well, when I used the word "configuration" in my post I was referring to the arrangement of elements. That is, a homemade half wave antenna vs commercial half wave, etc. Any configuration of elements that can be stuck inside a fiberglass tube can be easily made with wire elements. And there will be no difference in how they perform electrically.

Bob

[Vinny&Shawn]

[quote=johngsandusky;2097466]I want to install an antenna aloft on my mizzenmast. I'm worried about adding holes

John, it would be nice if you responded to all these posts,let us know what you nave decided, people seem to be off on an tangent.

[SV Papillon]

If you mount the antenna on a spreader then the antenna must be of the 5/8ths wave or 1/2 wave type, as there is no metal on the spar for the counterpoise (called a ground by folks that dunno no better)...it's not really a "ground" as the antenna must see an electrical representation of itself to function properly.

What is the prefered method for mounting a VHF antenna and SSB, whip or long wire on a solid or box wood mast??

I want to finally have a SSB and VHF that really works

JAke

[johngsandusky]

They are off on a tangent.
I haven't decided. I'm sure that much of the advice here is sound, but it doesn't really help me. I'm not going to put the antenna atop the mast, seems too much work for a small gain in height. If I attach a block, it will be to the side of the mizzen. But advice above seems contradictory. The antenna needs metal nearby, but shouldn't be close to metal. I figure I'll just read the instructions with the radio and antenna.

[Banjo]

If you can get inside the mast for the coaxial cable, you don't need the antenna, just peel back the black covering on the coax, carefully, for 21 inches, exposing the braid. Then using your pointy marlinspike or the point of an icepick, carefully work to loosen the braid where the black part ends, and fish the opaque center conductor through the braid without breaking it. Straighten the opaque part, straight up for 17-19 inches, and turn the braid downward and tied it with the black part of the coax....then slip a large piece of heat shrink over the entire think and heat it with the missus hair dryer....VOILA instant antenna that I betcha works as well as the umpty ten fourty sawbuck one....epoxy it in place inside the spar.....UH....This only works with WOOD spars......

I would only do this in an emergency if your REAL antenna has come to grief

Transmitting for any length of time on an unballanced line with high VSWR will result in cooked final transistors in your radio, something not many people can repair on the water. If you have to use non tuned antennas for any reason then I would recommend buying a tuner/vswr meter compatible with your intended frequencies you will most often use.

Even if you use a commercial entenna you should still do a VSWR test to make sure it is installed and tuned correctly, this will save your transmitting equipment and maximise power output from the antenna.

I may have responded a little too soon, I continued to read on and what the others say is all good advice..
Antennas and radios is a wholle new ball game, it's fun to experiment, I have been doing it for years making antennas for all bands from 3 Meg to UHF.
Add a boat to the mix and it's a new challenge again. :)

To answer you first Q, use bands to fix the antenna to your mast. Small screw holes well sealed will not hurt your mizzen.

[jerry bark]

I am no expert on antenna's but I do know this: darn near any antenna of the right length will allow you to listen with your VHF. However, in order to transmit effectively you must have an antenna/coax/radio that is all connected properly and working as a system. if you choose to make your own antenna you had better be able to assess the whole system before you risk your life on it.

That said, I would not use a homemade coax antenna if i intend my radio to serve as safety equipment. If all you expect is that it allows you to notify the drawbridge operator, or to ask for a slip then fine but if you think your safety will be on the line when you use your radio I would buy the best antenna I can find and mount it as high as is practical.

with any VHF radio remember this rule: just because you can hear others that does not mean that anyone can hear you

cheers
jerry

[johngsandusky]

I'm definitely going to purchase an antenna with the radio.
Does the cable length matter?

[RFNK]

Talk about overcomplicating things! Get some 316 stainless and bend and cut it to make a bracket that can be screwed to your mast and also create a base for your antenna. Some antennas come with the bracket ready made but make sure it's really 316 stainless steel. When screwing the bracket to the mast, drill out small holes where the screws are going to go, that are about three times the diameter of the screws and about half as deep as the length of the screws, and fill these with epoxy glue. Once the epoxy has gone hard, drill holes for the screws and fasten the bracket. Measure the distance from the bracket to your radio via the most efficient path (don't forget to leave a little drip loop where the cable passes through the deck) and then buy the standard cable length that'll do the job. Rick

[MarkH]

cable length does matter, the longer the run the more the signal loss, can't remeber the figures but rg58 cable loses 2 to 3Db for every hundred foot

my 2 pen'th on the diy antenna ideas...

the wavelength at marinf requencies is 1.92 metres, so a piece of sold wire or that length attached to the centre core of the coax will give you a full wave antenna

if you have the room inside the mast, get 2 peices that length, fit one at the top and solder the centre core of the coax to the bottom of it, and and put the other length of wire under below and solder the outer screen of the coax to the top of that.

that'll give you a full wave dipole aerial, which is very efficient

cheap but effective!

[johngsandusky]

Interesting idea. I think probably leaving the mast in the boat and attaching an antenna to it is more economical of time and money.

[Vinny&Shawn]

Interesting idea. I think probably leaving the mast in the boat and attaching an antenna to it is more economical of time and money.

It seems to me that everyone is off the deep end on such a simple installation. Yes mount it to the mast as high as possible,length matters only slightly,most radios will transmit, 25 to 40 miles atop the mizzen near coastal,if you can put it on the main all the better. Mine is tucked in next to the main mast by the spreaders,works fine.
As you said comes with directions,easy to install, do a neat job and enjoy it. Epoxy is not necessary in the screw holes,use a proper taper drill, a little bedding compound, good to go!

[BarnacleGrim]

Any ideas on how to run the cable down a solid mast? I need to install both a steam lantern and a VHF antenna myself. And perhaps also a 450 mHz antenna for an internet connection as well.

[johngsandusky]

I'm thinking wire clips to run the cable down. Can't wrap ties around the track. I hope to stick them on too.

[paladin]

There are some plastic stick-on devices that have little built in loops for tie wraps....stick them to the mast, then attach the cable with tie wraps. How long is the antenna and does it have a little plastic tube in the middle of it, or a fat base...do you have a part number for it?

[Vinny&Shawn]

I'm thinking wire clips to run the cable down. Can't wrap ties around the track. I hope to stick them on too.

There are nylon cable clamps that come in many sizes,which are designed and appropriate for attaching cable to the mast.And yes they have to be attached by screws. Properly bedded and with yearly inspection these clamps could last oh! maybe 35 to 60 yrs.With no degradation to the wood. I have had them on boats from 25 to 64 years old and they are the least problem,if any at all. My feeling is that anything that sticks on is trouble. We are talking ocean environment, right! There is nothing better than a row of clamps held tight by screws, insurance in a hard blow knowing it won't all come down on you when you need it most. Not to mention, if you have to go up the mast for any reason, you won't be dislodging any stick-ons with your feet.

[paladin]

I don't like screwing anything to a wooden mast.....it's just another place for water intrusion no matter how well that you seal it...
The clips that I refer to held wiring in my boat for years without coming loose. I'll have to check my tool box for some spares.....

[johngsandusky]

Thanks guys.
Paladin, no, I haven't bought it yet. I'm visiting the boat in FL for a week starting wednesday. I'll be buying and installing the radio then, as well as testing on board equipment.

[Dan McCosh]

FWIW, I used the stick-on clips for years, and they did occasionally come loose. Nylon is not UV resistant, so both the stick-ons and screw-ons deteriorated in sunlight, as did electrical ties. All are a pain when the mast needs varnishing, as is an external wire. Finally ran the wire down the inside of the mast, when it was being rebuilt. We've had an antenna bracket screwed to the mast for about 20 years, with no problems. It is in a hardwood block that also blocks the standing backstay, however. The aforementioned epoxy-hole works fine, if there is some concern about sealing. Another trick is a brass threaded zert--which make R&R very simple.

[johngsandusky]

Thank you all for your input. I'm flying down to the boat tomorrow, I'll let you know how the radio install works out.

[Dale Genther]

On our previous boat we installed one of those B&G wind speed /direction masthead units. Like palidin I didn't think screwing clips into a wood mast was a good idea and I couldn't run the wire inside the mast. I ended up using the black UV resistant wire ties to attach the wire to the port upper shroud and running it down to a waterproof thru deck fitting. I had to replace the ties every few years due to the UV making them brittle. Other than that it worked fine. I attached the whirlygig unit to the SS masthead fitting with two lagre stainless steel hose clamps that encircled the masthead unit and an "L" shapes SS bracket for the whirlygig. Whole installation took only a few minutes up the mast and put no holes in the mast. Maybe something similiar would work for a VHF antenna.

[floatingkiwi]

Crikey. Facing the same problem in the hopefully near future, I was tinkin about carving out a nice clean channel under the track and epoxy or 5200 a strip of wood to close it off again. Oh and stick some wires in there halfway between all that, lest I forget.

[johngsandusky]

OK, here's what we did: put the antenna on the main spreader instead. There are existing holes in the mast below the spreaders for lights. We got the wire up through the mast by drilling a new hole in the forward side of the mast below deck (the old hole is filled with wires) and getting it through with an electricians fish and some line.