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Old 23-04-2010, 10:55   #1
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Antennae at the Masthead

We have now bought our Option Globesurfer III voice/data terminal, our Ubiquity bullet, various antennae and cables, and we're just about ready to hook it all up.

And now the big question: where the h*ll to mount the antennae? The WiFi antenna and the cellular antenna are both about 80cm long.

Do I put them right up on the masthead? That will make quite a forest, and I'm not even sure how I would do it. We might have to buy one of those ring bracket things to fit it all on together with the windex, vhf antenna, anchor light, tricolor, and other crap up there.

Or do I put them further down on the mast somewhere? Obviously they'll be blanketed (electronically) by the mast at some angles, but that doesn't seem like the end of the world. They will be better protected from lightning further down. And won't interfere with the gear already at the masthead.

What do you guys think?

Also -- anyone ever use a really long (like 100 feet) coax cable for a cellular terminal like the Globesurfer? Do you need a signal amplifier?

Cheers, D*ckhead
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Old 23-04-2010, 12:00   #2
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You have a problem in the context that putting multiple antennas in close proximity can cause parasitic interaction between/among them just as much, if not more so than placing one or more down the mast which presumably is aluminum causing a similar issue. Regarding both the WiFi and cell phone antennas, the inherent signal loss for a large run of typical coax could negate any value in raising them to that height unless you are using VERY low-loss coax.
Considering the signal loss of the coax, it might be better for the VHF antenna efficacy to not place anything which can cause interaction or, at a minimum, ensure there is no interaction if you do co-locate them.
Every boat and every installation is different so someone's experience in doing similar is likely irrelevant. The only certainty is that you don't want antennas for entertainment (wiFi and cell phone) to interfere with that for the VHF.
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Old 23-04-2010, 12:14   #3
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Are you really going to climb up to the top of that mast scary enough just climbing ours. Take the camera up if you are going

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Old 23-04-2010, 12:28   #4
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Mount the Wifi antenna on the stern. Get it up 10-12 feet off the water and you'll get good service. A simple 8-10 foot piece of stainless tube secured at the deck and the top of your stern rail will serve well.
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Old 23-04-2010, 12:45   #5
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Are you really going to climb up to the top of that mast scary enough just climbing ours. Take the camera up if you are going

Pete
I still can't believe it myself. Our masthead is 75 feet above the water, which is like standing on the roof of a 7-story building. I'm going to need to wear some Pampers when I go up, I'm afraid.

I will take a camera. I suppose France should be visible from there; anyway I'm curious.
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Old 23-04-2010, 12:52   #6
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Originally Posted by S/V Illusion View Post
You have a problem in the context that putting multiple antennas in close proximity can cause parasitic interaction between/among them just as much, if not more so than placing one or more down the mast which presumably is aluminum causing a similar issue. Regarding both the WiFi and cell phone antennas, the inherent signal loss for a large run of typical coax could negate any value in raising them to that height unless you are using VERY low-loss coax.
Considering the signal loss of the coax, it might be better for the VHF antenna efficacy to not place anything which can cause interaction or, at a minimum, ensure there is no interaction if you do co-locate them.
Every boat and every installation is different so someone's experience in doing similar is likely irrelevant. The only certainty is that you don't want antennas for entertainment (wiFi and cell phone) to interfere with that for the VHF.
Well, the WiFi antenna will connect directly to the Ubiquity, so here is 0 run of coax and no losses. It's Ethernet from the masthead down, which is basically loss free up to much longer cable runs than that.

The GSM antenna is a different story.

The benefit of height is tremendous. Having the antennae at the mast head or at least well up the mast will make a lot of difference. It would sure be easier to mount the antennae on a pole on the afterdeck, but I sure would be giving up a lot of range.
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Old 23-04-2010, 13:03   #7
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Have to admit when it came to running a second ariel for our AIS, I chose the pole on the stern route.

Luke at Percy M See Chandlers has a 12 foot length of 1" S/S if you change your mind.

Are you using a bosuns chair? I found it difficult because you are at head height to the top of the mast rather than above working down wards. Ended up buying a flexible mast ladder which allows your to change position. Still scary though and we are only 40 feet. Tools go up seperately in a tesco shopping bag.

Hurst Marine - The Home of the Get-Up Mast Ladder

Shout if you need a hand this weekend, I am only in Fareham, Pete 07768 288763
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Old 23-04-2010, 13:12   #8
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The GSM antenna is a different story.

The benefit of height is tremendous. Having the antennae at the mast head or at least well up the mast will make a lot of difference. It would sure be easier to mount the antennae on a pole on the afterdeck, but I sure would be giving up a lot of range.
If you want to determine what, if any, benefit derives from raising the antenna, it's easy enough to determine but we need to know what type coax you are using to determine loss. I only commented to ensure you are aware of the trade-off.
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Old 23-04-2010, 13:19   #9
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If you want to determine what, if any, benefit derives from raising the antenna, it's easy enough to determine but we need to know what type coax you are using to determine loss. I only commented to ensure you are aware of the trade-off.
Hi: Well, I haven't bought the coax cable yet. I thought ultra low loss, and that type which is meant to buried.
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Old 23-04-2010, 13:26   #10
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Have to admit when it came to running a second ariel for our AIS, I chose the pole on the stern route.

Luke at Percy M See Chandlers has a 12 foot length of 1" S/S if you change your mind.

Are you using a bosuns chair? I found it difficult because you are at head height to the top of the mast rather than above working down wards. Ended up buying a flexible mast ladder which allows your to change position. Still scary though and we are only 40 feet. Tools go up seperately in a tesco shopping bag.

Hurst Marine - The Home of the Get-Up Mast Ladder

Shout if you need a hand this weekend, I am only in Fareham, Pete 07768 288763
Hi Pete: Very kind offer. I won't be doing it this weekend, but rather next. If you're around then you're welcome to come by; if not to help then to have a drink on board at least. Are you going to the Moody club get-together in Yarmouth on May 9? We will be sailing then and thought we might stop by if we're back far enough east by then.

Yes, I use a bosun's chair plus a rock-climbing harness for safety, and two halyards. Yes, it's a problem at the masthead. I can't use any of those nifty mast ladders because we have a furling main and no regular luff slot. I thought about putting two steps up there but then you're no longer held by the bosun's chair. I don't quite know the best way to do it.
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Old 23-04-2010, 14:13   #11
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Hi: Well, I haven't bought the coax cable yet. I thought ultra low loss, and that type which is meant to buried.
"ultra low loss" is a marketing term in many cases so you might want to compare various types before you end up worse off than you are now. For example, the ubiquitous RG213 coax with a non-contaminating jacket yields almost 3dB loss for 100 ft or an efficiency of 57%. Link below is a good comparative tool:

Attenuation & Power Handling Calculator
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Old 23-04-2010, 14:42   #12
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DH, sorry can't do the 9th, although the Solent Branch asked me to act as the host. Unfortunately I am away diving on the Sunday. I am acting as the host for the 1-3 May weekend at Thorney Island too.

However could meet up for the 25th birthday party at the end of May, that looks to be a really good do with dozens of Moodys attending.

Do you have a trysail slot? we have inmast so they made the mast ladder with a 5mm luff bolt rope which runs in the trysail slot instead of normal sail slides.

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Old 23-04-2010, 16:31   #13
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[QUOTE=

And now the big question: where the h*ll to mount the antennae? The WiFi antenna [/QUOTE]

I think wifi reception will be limited by low power/uni directional antenna before you lose reception by over the horizon effect that only height will improve.

For vhf/ais height is definitely the way to go with a backup stern mount.

Presently we have coax running up the back stay to fixed vertical antenna at top of mast. I'm thinking of mounting the antenna with slides on the backstay itself and hoisting it up with a light halyard. As antenna is raised there will be a padded bracket ( shaped so as not interfere with main halyard etc)which will be forced against mast in the inverted "V" to give stability and allow antenna to extend above mast without flopping around. plastic ties keep the coax against stay and could also retain halyard tail. Simple to install, simple to maintain and no fear of heights involved other than initial pulley install -could also be used for masthead light too!
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Old 23-04-2010, 21:00   #14
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Dockhead-
If you buy cellular cable from the Pope himself, you still can't get zero signal loss in it. You will find the signal loss, even for top quality cable, quickly negates any gain from antenna height, so for this you are better off compromising toward a shorter cable run.
Regarding range, at least in the US, the cellular systems are or at least used to be programmed so that the tower will intentionally DROP YOUR CALL if you are more than 32 miles from the tower. This is based on the system measuring propogation delays in your connection, there's nothing you can do about it. The idea is that if you are that far away, surely this is the wrong tower to be handling your call, so they drop it.
Now, if you figure any coastal tower is probably on a TOWER...100' tall? 150' tall? and then use the "horizon distance line of sight" calculations with your antenna height, combined with the tower height, you can figure out how far up your antenna needs to be, to get that 32-mile maximum range. Extra power won't matter, the carriers will drop your call based on signal delays. A bidirectional signal booster will certainly help--but it won't push the range past tha tmagic number, unless the carrier has allowed for it in their software.
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Old 24-04-2010, 06:04   #15
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I am constantly amazed at how much collecive knowledge there is on this site. Thanks so much for the information. I had no idea that cell phone towers work that way.

I guess in light of all this information, the antennae should go on a radar pole on the afterdeck. That will simplify everything, won't it? I need one of those anyway because I don't have an outboard hoist.

That will avoid the long cable runs and the weight at the masthead.

It will also enable me to get three other antennae off my stern rail (navtex, gps, satphone), and give me a place to mount a searchlight.

Thanks! I hope his conversation ends up being useful to others, as well. I'll report here how it all works out.
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