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Old 06-06-2014, 16:02   #151
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Re: Please Recommend a Quality VHF Masthead Antenna

Hi Y'all,

I've seen this statement a couple of times, and I feel the need to speak up: "It is a dipole so less noise than base loaded designs which are ground plane antennas."

Most (if not all) marine "whip" antennas that have the form of a base coil and slightly over 3' whip are end-fed halfwave designs, and are NOT "base loaded" or "ground plane antennas". The coil is simply matching the high impedance of the end-fed half wave radiator, and the antenna is not dependent on any sort of ground plane - they work fine bolted to the side of a wooden mast or cabin trunk, unlike most antennas intended for mounting on a vehicle roof or trunk lid, which do not work well at all absent the sheet metal underneath them.
"Base loaded" would be an appropriate description for an antenna where the radiator is less than a resonant length - CB (27 MHz) antennas commonly have such an arrangement, as a full quarter-wave is too large for most vehicles. "Ground plane antennas" expect to have a conductive ground plane available at their mounting point, which effectively functions as a counterpoise to the radiating element(s) of the antenna. These antennas generally perform poorly without some sort of ground plane, though it often takes less metal than you might think - a metal spreader or masthead is often sufficient at VHF or especially UHF.

73 DE Hartley
S/V Atsa
W1OQ
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Old 06-06-2014, 16:07   #152
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Re: Please Recommend a Quality VHF Masthead Antenna

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Originally Posted by Hartleyg View Post
Hi Y'all,

I've seen this statement a couple of times, and I feel the need to speak up: "It is a dipole so less noise than base loaded designs which are ground plane antennas."

Most (if not all) marine "whip" antennas that have the form of a base coil and slightly over 3' whip are end-fed halfwave designs, and are NOT "base loaded" or "ground plane antennas". The coil is simply matching the high impedance of the end-fed half wave radiator, and the antenna is not dependent on any sort of ground plane - they work fine bolted to the side of a wooden mast or cabin trunk, unlike most antennas intended for mounting on a vehicle roof or trunk lid, which do not work well at all absent the sheet metal underneath them.
"Base loaded" would be an appropriate description for an antenna where the radiator is less than a resonant length - CB (27 MHz) antennas commonly have such an arrangement, as a full quarter-wave is too large for most vehicles. "Ground plane antennas" expect to have a conductive ground plane available at their mounting point, which effectively functions as a counterpoise to the radiating element(s) of the antenna. These antennas generally perform poorly without some sort of ground plane, though it often takes less metal than you might think - a metal spreader or masthead is often sufficient at VHF or especially UHF.

73 DE Hartley
S/V Atsa
W1OQ
Great information as we DO have a wood mast (and a carbon one on the race boat).
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Old 24-06-2014, 12:53   #153
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Re: Please Recommend a Quality VHF Masthead Antenna

We have a 44' wooden mast and are thinking of getting the Glomex RA106SLSSB18 whip for a Standard Horizon GX2200 (first electronics after 30 years out of the water-we've been restoring for 6 months so far); I'm not sure if that's ground-plane or not and would work as you suggested but am wondering if you could advise? We plan to cruise but are looking at another year before we are ready...will be rigging and stepping the mast this summer and are wanting to take this opportunity to get something for the long haul...
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Old 24-06-2014, 13:22   #154
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Re: Please Recommend a Quality VHF Masthead Antenna

Hi,

The Glomex RA106SLSSB18 appears to be an end-fed half wave type, so it should function properly on your wooden mast. I can't say I'm thrilled with the "solderless" connector they advertise (I don't know anything about this specific connector, but in general I've seen very poor results with solderless connectors in a marine environment).

Hartley
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Old 09-11-2015, 14:14   #155
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Re: Please Recommend a Quality VHF Masthead Antenna

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Yes but the Metz still is a GP based antenna with loading coil. It is probably the best of them though. What I like so much with a dipole is that it is not grounded to the boat which means you often have less noise on the radio.

p.s. I also have one of those simple emergency antenna's, also from Shakespear I believe. Just a piece of coax cable with an 8" antenna or something and it works surprisingly well and is handy with testing things.
For 2m and 70cm, these are very nicely made roll up antenna's that might be handy for an emergency:

Slim Jim Info

I had great service with him with delivery here to the UK.

Only relationship with him is as a customer.
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Old 09-11-2015, 17:19   #156
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Re: Please Recommend a Quality VHF Masthead Antenna

I'm planning to use one antenna for VHF and AIS (with a splitter). Would I be better off with the Shakespeare 5400-XT, or the 5396-AIS which is a purpose built antenna with a bit wider band to include the AIS frequencies a bit better. Beyond the wider band of the 5396-AIS, I'm not sure what the difference is other than Shakespeare says that the 5400-XT reads DC open, where the 5396-AIS reads DC shorted.
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Old 10-11-2015, 03:52   #157
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Re: Please Recommend a Quality VHF Masthead Antenna

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Originally Posted by Saltyhog View Post
I'm planning to use one antenna for VHF and AIS (with a splitter). Would I be better off with the Shakespeare 5400-XT, or the 5396-AIS which is a purpose built antenna with a bit wider band to include the AIS frequencies a bit better. Beyond the wider band of the 5396-AIS, I'm not sure what the difference is other than Shakespeare says that the 5400-XT reads DC open, where the 5396-AIS reads DC shorted.
Salty,

Check out the broadband antenna from Vesper. They supply AIS transceivers and have developed an antenna for this market. The specifications of the Shakespeare antennas are not clear enough to tell whether either antenna is really good for combo AIS/marine voice applications.

There are antennas that don't work well with AIS thus we see companies marketing specifically to the AIS splitter users. I would guess that Shakespeare think their AIS marketed antenna is better for AIS but they sure didn't instill any confidence in their written specifications.

Installation is important. For lowest VSWR don't install the antenna within 3 ft (1 M) of any other vertical metal structures or other antennas. And follow all the manufacturer's installation instructions.
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Old 10-11-2015, 08:48   #158
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Re: Please Recommend a Quality VHF Masthead Antenna

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... Installation is important. For lowest VSWR don't install the antenna within 3 ft (1 M) of any other vertical metal structures or other antennas. And follow all the manufacturer's installation instructions.
Thanks Dan. Your comment WRT installation near "vertical metal structures" actually brings up another question. All of the lightning protection methods I've read include installing a "grounded lightning terminal" that is higher than anything else, including the VHF antenna. I had been planning to install a 1/2" aluminum lightning terminal on one side of the masthead, and the VHF/AIS antenna on the other side, where said lightning terminal would be a foot taller than the antenna. The distance between them would be slightly less than a foot (the width of the mast). I take it from your comment that this might be a bad idea?
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Old 10-11-2015, 11:05   #159
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Re: Please Recommend a Quality VHF Masthead Antenna

Is it a "bad idea"? No, I don't think it's a bad idea. But lots of masts don't have pointy rods. Lightning is basically a random thing and whatever you do only shifts the odds a little bit one way or the other. There are no sure fire ways to prevent damage.

The rod will reduce the signal of your AIS and VHF voice comms at some bearings. By how much is hard to say with certainty. Basically if you feel more comfortable with the rod then install it. Check your VHF range by driving the boat in a slow circle (really slow) and looking at AIS targets. If there is a blind spot at a certain bearing it should be readily visible as AIS targets fail to update. You could also hail some boats at various bearings and ask about your quality of signal. If all bearings allow adequate contact then don't worry too much about it.
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Old 10-11-2015, 11:33   #160
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Re: Please Recommend a Quality VHF Masthead Antenna

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The antenna matters a bit
Good feed line at least as much
RG213 is a good start
LMR400 with N connectors will give at least 25% more power to the antenna
LMR or Andrew - either one makes all the difference in the world

Also, don't forget - no sharp bends!
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Old 13-11-2015, 04:17   #161
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Re: Please Recommend a Quality VHF Masthead Antenna

Quite by accident, after a thread on the forum about binoculars, and with first hand experience of some truly superb optics and lens coatings coming from China (I am an amateur astronomer with a more than usual emphasis on 'amateur') at extremely low prices, I was struggling to come up with a source in America (not knowing anything about American Retail), and the first name I came up with panned out with examples of very good and very cheap binoculars - Walmart. I do appreciate that there are people that will not darken Walmart's doorways, however. *grins*

Since then I have looked at a few of their marine items (as likely obtaining a boat in America or Canada relatively soon, and they seem to have a fair few branches . . ), and have come across this presently on Sale offer, which may be useful to people on that side of the Pond, as it does seem to be a very good antenna:

206 Metz MANTA-6 40 Stainless Steel VHF Antenna

206 Metz MANTA-6 40 Stainless Steel VHF Antenna - Walmart.com

Down to $47.03 + $8.09 shipping

Hopefully that helps some of you out.
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Old 14-01-2016, 10:10   #162
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Re: Please Recommend a Quality VHF Masthead Antenna

a VHF antenna at top of mast is vulnerable to lightning strike
Would it be better to mount on a non-conductive bracket on spreaders (still subject to induced currents) or mount on deck away from stays and forgo the additional miles gained with a masthead mount
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Old 14-01-2016, 10:25   #163
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Re: Please Recommend a Quality VHF Masthead Antenna

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My existing masthead VHF antenna is a skinny steel whip combined with winded, fed by a skinny coax cable. My mast is down and I'm taking the chance to replace everything.

I have no complaints about VHF comms. I use an Icom M604 and get good signal reports from great distances (75 feet of height probably don't hurt), but why not take the chance to install something good? Anyone have any recommendations?

Maybe some kind of dual band VHF/UHF antenna? I now have an amateur radio license and might play around with the VHF/UHF amateur frequencies - guess I could use an antenna switch.
Keep them seperate. One antenna to solve all problems is always a compromise.

Those stainless whips are simple and reliable.

If it aint broke do you need to fix it?

I'd focus more on making sure the coax and connectors are in good shape.

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Old 14-01-2016, 10:40   #164
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Re: Please Recommend a Quality VHF Masthead Antenna

Hi,

The masthead antenna is definitely vulnerable to lightning destruction - but it also gives maximum range.
So the answer depends on how you foresee using your VHF - if you don't see a need for more than 5-8 miles range, then a deck-mount antenna (say a masthead 1/2-wave on a 4' extension pole or similar) will be less vulnerable - and have a shorter cable run, which is also a good thing..

On the other hand, if you think you might want to talk 20+ miles, masthead is the way to go - you can't buy the range any other way.

On Atsa, I have both - the Nav station VHF is connected to the masthead antenna, while the helm radio is connected to a GAM whip on a 4' extension mounted on the pushpit rail. I find the "around the bay" range is more than adequate, and I'm not distracted by folks chatting (on 16, naturally) 30 miles away - tho I can hear them on the nav stn radio if I want.

If you're cruising in a seriously lightning-plagued area (Tampa, Central America, etc.), I would consider carrying a spare antenna (with coax) AND radio - they're really not all that expensive and you don't need fancy features.

73 DE Hartley
S/V Atsa
Currently in La Paz, MX
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Old 15-01-2016, 16:58   #165
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Re: Please Recommend a Quality VHF Masthead Antenna

Convention is to have less than 40% loss between transmitter and antenna. You have a 77 ft mast plus the distance run inside the boat. Try to use at least RG-213 RF cable. If you can pull the cable all the way from the masthead to the navigation station (vhf transmitter) without a splice it is better because splices are a source of loss and usually don't age well. Leave some extra slack so that when you next pull the mast you have enough for a splice.

Put a drip loop in the cable under the antenna at the masthead. Don't wimp ojt and use solderless connectors. Solder and seal the connection at the antenna as suggested above. I called in an experienced/reputable marine technician just to do this (didn't trust myself or the riggers).

I went for the wire Shakespeare. My understanding is that no antenna survives more than 5-10 years and the fiberglass ones are brittle, stiff, suffer UV damage and have more windage.
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