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Old 15-02-2013, 07:58   #16
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Re: Coax Cable Types

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Originally Posted by colemj View Post
That is why I implied that you may be over-worrying this and that losses will be within performance expectations.

In other words, I bet you are losing that last 1 or 2 miles of reach with your current VHF setup, but this is not important in practice.

The same will most likely be true for your phone and SSB usage.

It is very easy to get caught up in technical specs with radio gear and spend a lot of time, effort and money believing you are squeezing out performance gains - when performance is actually relative, variable and controlled by many other factors than just the coax.

Unless you know you will always be hanging by your toenails on the very far edge of a signal, highly specialized installations will not be noticeably different than lesser ones.

If constant strong connections are that vital to your business then it would be better to plan your passages and anchorages around that fact rather than hope expensive gear and installation takes up the slack.

But this is a decision that only you can make. If it is going to eat you alive thinking about it all the time, then peace of mind is worth something.

At the very least, put most of your worry into the connectors. Most otherwise good installations are half wasted because of losses in the connectors. Pay for good ones and make sure they are installed correctly. Use quality N-connectors and not cheap PL259's - convert when needed with quality N-PL259 converters.

And since I am advocating not worrying too much about the coax cabling, I need to confess here that our SSB and Ham are wired with 3/4" Heliax! I recently removed the 1/2" Heliax connecting our VHF and replaced with LMR400 (following a lightning strike where I did not trust the coax any longer and thought the Heliax was overkill on a VHF - the LMR400 is also overkill, though). But in my defense, this was already installed on our boat when we bought it. Personally, I would have used LMR400 (and N-connectors).

As for your experience with the Bullet, I believe you do not have it configured correctly. There should be no need to monkey with your computer's IP configuration each time you want to access the software or change locations. You should always be able to simply open the software web page and choose the access point you wish to use. To change AP's, you just click on a different one.

Mark
Thanks, Mark.

If you have a different way of connecting to the Bullet, I would be eager to hear about it. As far as I understand from reading the manual, and confirmed by the IT guys in my office, you have to set a fixed IP in the computer you are using for configuration, then access the AirOS interface of the Bullet with its IP address. It's a bit of a PITA, so if there is another way to do it, I'm all ears.

As to coax cable -- keep in mind that attenuation is radically different depending on frequencies. See:

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The highest VHF frequencies are in the range of 162 megahertz. LMR 200 will only give 4.1dB per 100 feet, whereas at 2.4 gigahertz, the attenuation is 16.5 dB. It makes a big difference what frequency you're dealing with!
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Old 15-02-2013, 07:59   #17
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Re: Coax Cable Types

I work with LMR400 a lot. You could try a 6 db omni antenna. I work with 6db, 9db and 15db antennas but I don't have to worry about FCC regulations. The 6db has the best vertical propagation of the three. Amplifiers are also available to boost the signal at the antenna but I try to avoid them. Connectors lose 1/4db each. Make sure to seal the external connectors with rubberized tape and then a good quality vinyl tape like super 33. Don't cover the drain hole on the antenna if it has one.
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Old 15-02-2013, 08:25   #18
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Re: Coax Cable Types

For your cellular antenna, I don't think the increased attenuation is worth the additional distance to the horizon that you get by having the antenna higher on the mast. Although I have received cell calls miles out at deck level, the power that cell sites and your phone broadcast at are very limited, compared to something like your marine band VHF.
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Old 15-02-2013, 08:35   #19
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ColemJ gives excellent advice.

N connectors are better sealed than PL-259. They are a better impedance match at 50 ohms and most important above 1 gHz. If you take pains to weather seal PL-259 connectors they are just fine at HF and VHF without significant loss.

Chip
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Old 15-02-2013, 08:56   #20
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Re: Coax Cable Types

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Originally Posted by David M View Post
For your cellular antenna, I don't think the increased attenuation is worth the additional distance to the horizon that you get by having the antenna higher on the mast. Although I have received cell calls miles out at deck level, the power that cell sites and your phone broadcast at are very limited, compared to something like your marine band VHF.
So you're saying -- don't put it on the mast at all? I was planning the lowest spreader, which is 10 meters above the keel, for a total of about 15 meters of cable run or 50 feet.

I guess I could put it on the pushpit, but that would still be a fair cable run, say 10 meters I guess.

If only I could put the radio right on the antenna, like the Bullet. But that's not practical because I need to be able to change SIM cards and so forth.

I guess I could put the radio in the lazarette, and the antenna on the pushpit . . . run Ethernet and phone cabling from there to the nav table . . . that would radically shorten the cable run.

On the pushpit, the height above the water will be decent, say 2.5 meters or so.

That's not the same as 10 meters, however. Surely a bit of height will really help a lot? Hmmmmm.
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Old 15-02-2013, 12:09   #21
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Re: Coax Cable Types

Dockhead-
If I may suggest, also check the type of insulation in the cables you are looking at. Low-loss often will use an airy foam, which may absorb water (bad thing on a bad) and may get crushed by the tie-offs. You will want to pay attention to how the cable is secured, because they all distort under their own weight when run vertically, and either they distort over time, or they distort from the "crush" of whatever you've tied them off with, so take a look at the options and make some informed choices about how to run it for the best long-term performance.

If you are putting on the end fittings by yourself, and aren't experienced at that, you may want to hire it out, or else buy a few extra fittings and some extra feet of cable, and make a few practice connections first. (If #1 is no good, lop off six inches and try again, etc.)

There's more than just selecting the right cable, to get the best performance out of it.
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Old 15-02-2013, 12:24   #22
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Re: Coax Cable Types

Hi Dockhead, I do a fair bit of GSM modem design.

While the noise floor on modern GSM receivers is very low, its very difficult to transmit signal any sort of distance, at marginal distances that would benefit you at the receiver ( phone), using a remote antenna.

Hence there is little to be gained using external antenna for a mobile phone ( how are you connecting it in anyway). There is some benefit for GSM modems to be placed up 15-20 feet , if the receiver goes up their with the antenna.

Ive had several GSM antenna solutions on several boats,using good quality 8' banten antennas , Id have to say in summary the effort wasn't worth it.

ALso large diameter co-ax is heavy and will put significant strain in the strain relief solution at the top of the mast , not to mention the connectors issues and connector incompatibility.

remember to that the timing solutions on GSM mean that distance from receiver to transmitter is limited , irrespective of power. You can find in urban areas the Timing advance is set as to prevent phones further away from gaining access.



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Old 15-02-2013, 12:55   #23
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Re: Coax Cable Types

This has been a great thread. Thanks.

From the comments, I would conclude that a fixed antenna on the spreader for GSM is probably alot of work and cost for rather little gain... is this correct?

Would there be any benefit to a movable/aimable "temporary" GSM antenna with maybe 6m of cable that could be raised by halyard when the permanent deck-mounted GSM antenna is marginal?

Also, what percentage of the desired signals will be from satellite? I can't see how a spreader-mounted antenna would be much use there.
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Old 15-02-2013, 13:03   #24
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Re: Coax Cable Types

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Would there be any benefit to a movable/aimable "temporary" GSM antenna with maybe 6m of cable that could be raised by halyard when the permanent deck-mounted GSM antenna is marginal?

Also, what percentage of the desired signals will be from satellite? I can't see how a spreader-mounted antenna would be much use there.
The losses particularly at the higher frequencies are quite large and the specifics of GSM timing and antenna placement of base station can mean that results are often non-intutitive.

My experience is that where your phone gets a signal, it is not enhanced by raising it more then a few feet , if in so raising it you separate the antenna from the receiver. ( even though in fact that often breaks the type approval of the phone!).

IN the case of GSM modems, where Wifi can be used or digital cabling to bring the resulting information , there is a marginal improvement in raising the complete modem about 15-20 feet. however often this does not lead to any increase in data rates.

Im not sure what you mean by satellites , GSM is exclusively terrestrial , Sat signals like GPS and Inmatsat/iridium are negatively affected by placing the antenna further away from the roll centre.

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Old 15-02-2013, 15:10   #25
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Re: Coax Cable Types

"Hence there is little to be gained using external antenna for a mobile phone ( how are you connecting it in anyway). "
Kinda depends on what the "walls" are made of. Case in point, simply getting an antenna on a car roof instead of inside the cabin, changes 2 bars to 4 (out of 5). If you are in the cockpit of a boat, you're already outside. But if it is raining and you are below, you have to ask how much the hull and deck are cutting your signal. Take phone, observe bars. Go below, observe bars again. If the hull is eating signal, then an external antenna may be very worthwhile.

As to how to connect it, yes, most of the new phones lack the connector. The old Palm Treos all had it (a little plug by the antenna stub) and even the newish Samsung Captivate has one, hidden behind the battery door. But since most new phones don't have a connector, companies like Wilson make active boosters. You put the handset in a cradle, or within the same room as a cradle, and the cradle contains a mini-site that connects multiple phones to an external antenna, with boosting in both directions.

YMMV, but the advantages are sometimes real, and the equipment is on the shelf.
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