VHF Antenna question

[WX]

I'm planning on putting my VHF antenna at the top of my mast, the down side is that it will restrict my access under one of the bridges on the local river.
Are the range advantages on a masthead mounting great enough to offset the above disadvantage?

[John B]

Put it on a spreader.

[WX]

No spreaders, this is a free standing Junk rigged mast .

[John B]

bugger.

[WX]

Just a bit. I'm seriously thinking of mounting it on the pushpit.

[John B]

PM Chuck and ask if you can put it inside the mast.. that'd be cool.

[WX]

I hadn't thought of that, sadly I don't have the antenna yet and I'm gluing the mast together on Sunday.

[Bob Adams]

VHF is line of sight, altitude is your friend. Somewhere there is a chart depicting antenna height to range ratio.

[paladin]

If the mast is wood, put it inside.....use the top 5-6 feet, make it from TV twin lead and coaxial cable from Radio shack or any radio shop...make the antenna for 2-3 dollars and will work as well or better than many of the so called hi gain ones.....I need three - four days to find the drawings as I am in dialysis tomorrow and Saturday. I wrote an article to do this for woodenboat but it was rejected so I'm putting it in a book I'm writing.

[WX]

Chuck I have read that I need 213U coax for VHF as the run is over 10metres, would you agree with with this?

[paladin]

If the run is 35 feet lemmee check my RF cable losses and I'll get back in a few minutes.

[Ian McColgin]

Presumably for a sail boat it's the short metal whip. It could be mounted on the front face of the mast rising no higher than the mast head if the bridge height is really that close. I've bumped the upper foot of a roughly 2' whip under a railroad bridge to no ill effect.

[WX]

The masthead antennas are 850mm in length, I think I could come down that far on the front face of the mast without getting in the way of rigging. I like Chuck's idea of the internal antenna though.

[John B]

sheesh.

[paladin]

Gary...I have the text but I can't find the drawings at the moment. I'll have to recalculate them. Get your cable ready, a soldering iron, some hot glue and electrical tape and about6 feet of a heavy copper wire. The coax should be about 3-4 feet longer than you really need, and also use rosin core solder. The 213 cable is better than the average stuff, and if you don't have cable yet, and it's available, try to get some supercable 9086IIA as it is a helluva lot better for VHF radios. If not, the 213 is fine. I'll start formatting the text and making the drawings on Friday. Tomorrow is dialysis for me. The only thing, the top of the antenna should be at least 6 inches away from metal if possible..

[redbopeep]

Chuck, we did as you suggested and put the antenna inside our foremast. Works great. I don't have the numbers on lengths, etc, I'll ask David tomorrow if he recalls it all--he's already asleep now.

About that glue-up, you just need to run a tracer line that you can pull the wire with. We put ours in an existing mast. You should be making sure you have room in there anyway for more than just your antenna wire--run a couple lines so when you decide later that you need something, you've got the line already run and you can just pull the wire you want in with it

[paladin]

Thanks...if he has a copy of the drawings please send it on to Gary, and send me one too.

[Stan D]

Chuck, are you talking about a J-pole? Way cool idea. I would suggest going one step further and use hard line for the coax. Somewhat expensive and not the easiest thing to find, but loss characteristics are great.

[redbopeep]

Chuck--somewhere in the mess that is David's computer is info you sent as well as his notes on what we did.

I'll see if I can dig for it myself later. We're in the middle of a gale here in Newport Beach. Sunny and bright but really windy! Our boat is fine on one of Newport's numerous moorings, but we're baby-sitting another cruiser's boat on a different mooring (death in the family took them out of town just now) and hubby is having fun (sic) rowing over to check their lines and make sure all is good there and then rowing back here. Each trip he makes I wonder if he's going to catch onto our boat or continue being swept by and down wind... I think he'll be spending the night on their boat since, according to the officials here, visiting vessels like ours and their must be occupied at night (and especially during storms) and I'd hate for him to be rowing out in the middle of the night to check the other boat. Always somthin'

[WX]

Okay, I'm buying the 213 coax on Tuesday when I'm in Brisbane. I can get it for $4.60 a metre up there. A local outlet wanted to charge me $4.80 a metre, would only sell it in 10 metre lengths and wanted to charge me a $25 cutting fee as well! Bloody nerve of some people!
I have a length of 12mm low pressure poly pipe ready to run up the middle, this will make feeding the coax through very easy next week. Thank you everyone for the feedback. Chuck I reckon I will go with your idea

[paladin]

The price of 213 here is 73 cents a foot in 35 foot lengths.....get good connectors and be careful when installing them that you don't get a fine hair wire from the braid between the center pin and ground.

[WX]

Thanks Chuck. How's the health going? Are you on a waiting list for new Kidneys, I assume that is why you are doing dialysis?

[paladin]

Yup..heart doc sez we gotta wait for a while to let the heart rest after the last little scare. One doc sez 6 months...Dr. Jacob sez maybe 4....I dunno...Dr. Huang is the boss and I ain't agonna argue.

[paladin]

Hi Gary....you will also need 6 feet of standard (not foam core) antenna twin lead wire, 300 ohms. I have most of the numbers....gonna strip one and use my spectrum analyzer to tune it properly after cutting and soldering just to make sure for you...hopefully this afternoon. Get some good goop for sealing the end of the coax.

[WX]

This is one of the things I really like about this forum, the level of knowledge and the willingness to help each other.

[paladin]

Gary....please send me a private e-mail address so I can send the Jpegs of the antenna drawings..... it's a bit much to do here.

[paladin]

and another thing......radar reflector.........get a large closable plastic sandwich type bag.......
some aluminum foil.......cut strips about 1/8th inch wide and 1/2 inch long...lotsa them
make some 1/8th inch wide and 2 inches long, another handful......
make some 1/8th inch wide and 3 inches long..........then several pieces crushed into loose balls in your hand...put the balls in the plastic baggy, sprinkle in all the little "spaghetti" pieces......stash in mast a foot down from the antenna with about 6 inches of the coax sticking up, tape or glue in place, close mast...cheap and dirty and it works.