Question for Thom or anyone else

Old 12-08-2002, 10:21 PM
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Dumb move of the week. Did not lower my radio antenna when I left the boat ramp. Now I need a new one.
I have seen ones in the catalogs that are dual mode Marine radio and Cell phone. The cost a bunch
more than a regular antenna, but extended cell phone range would be a great safety feature. Do they do a good job of extending cell phone range?
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Old 12-09-2002, 02:42 AM
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That is one of the reasons I was asking about a three footer ! I have seen that happen many times,
you are not alone..................TOMMY
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Old 12-09-2002, 04:57 AM
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These dumb things allow us to get new stuff. [img]/infopop/emoticons/icon_razz.gif[/img] I believe in redundancy; I don't like dual purpose anything on a boat if I can avoid it. In most instances you get a little less of both. When one goes down, like an antenna, you lose both. The real question Thom; does the dual purpose antenna with the cell take away, in any way, from the function of the VHF? I understand that you pick up a bonus, getting the cell antenna too, but do you give up anything? I'd get two, if you want this range with the cell phone. [img]/infopop/emoticons/icon_wink.gif[/img]
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Old 12-09-2002, 05:39 AM
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There, that was easy, I really don't know anything about those antennas. In general I would have written exactly the same thing that Mumbletone did, but I've have done it with more misspelled words and typos too.

OK, Here's what I suspect, take it for no more than a guess though because its not based on any firm knowledge. I suspect that in those dual purpose VHF/Cell antennas that you have two entirely different radiating circuts that just happen to be sharing the same tube. My guess is that in this rarest of cases that the functionality of the VHF is not effected by the pressense of the other radiating element (other than that it will have an effect on directionality which is unavoidable). So, I don't think it will detract from the VHF capability.

As to extended antennas for cell phones, that's a tough one. I've been using a separate cell antenna for a couple of years now, first an old Shakespeare one I had for a bag phone and then I switched over to a digital phone and got an antenna by Digital antennas for it. Both are mounted roughly 5 feet above the water level and both antennas were and are 4' tall. I never was or have been able to see any increase in phone range with either of those antennas connected vs. just the phone with its own antenna.

I do now know what the specific characteristics are of a radio signal in the frequency range the cell phones operate in but as a general rule they should be line of sight, they should also have the ability to penetrate or pass through some things as well though. Unlike our VHF signals, which will bounce off of buildings and such (which sometimes add significantly to our range) a cell phone will work inside the building because the walls are essentially invisible to them. One thing I am sure of is that unlike extremely low frequency signals they will not penetrate water, so they aren's shooting though some part of the ocean to reach our boats.

Anyway, back to real world. In this case I don't think one function of a dual purpose antenna will degract from the other. At the same time I doubt that internally the VHF side of the dual purpose antenna is well constructed (brass rods for radiating elements ranther than the center wire from the Coax for instance) and I have no idea about how the cell side of the things are constructed. Given a choice, as I was, and a desire for a cell antenna I'd still go for seperate sticks, and in fact that is what I have on our small boat to this day.


"Just because you're on their side doesn't mean they're on your side."
(--Teresa Nielsen Hayden)
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Old 12-09-2002, 03:00 PM
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I'm a electrical engineer in the cell phone business. I have never tried a VHF/UHF dual mode antenna, BUT...
I will say that the coax feedline losses are very high on both of our cell phone bands 800 and 1900 MHz. USUALLY, the only time it makes sense to use a remote antenna for a portable/mobile installation is to get the antenna out of a metallic vehicle (car/plane). I have a tendancy to believe that unless you fed this antenna right at its base and the antenna gives you some height advantage, then its not worth the trouble.
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Old 12-09-2002, 04:29 PM
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Maybe this site will help.
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Old 12-09-2002, 07:18 PM
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What is your opinion on cell phone boosters the ones that patch between phone and a high gain remote antenna that cost $200-$300?

Tim,25'Skip,Reel Hungry
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Old 12-10-2002, 08:48 AM
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Something like the jdteck bi-amp may work for you in marginal signal conditions for many TDMA, CDMA, and GSM phones. Note that the jdteck unit is only for 800/900MHz phones and not the pcs band of 1900MHz (so watch out if you are with Sprint). If you use a car adapter kit for your phone, then the rf/dc hookup will be much easier. And I mean the real one, the with a holder and automatic cable connections. Check with your service provider for the frequency band used in your area of coverage.
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Old 12-10-2002, 03:18 PM
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I know nothing of the dual use antennas, however as far as external antennas go I can give the following example.

When I visit Apalachicola in the spring and fall, I stay at Breakaway Marina. It is on the fringe area of the Apalachicola cell tower. This past October, I was calling home that evening. My wife complained that she could barely hear me and I was breaking up. I said holdon, pluged in my car antenna and she said, "Oh that is much better".

What kind of car antenna do I have? It is a simple 3 inch or so mag mount antenna that is stuck to the roof of my vehicle. I think it is advertized as having a 3db gain. Am I going to get one of the larger cell antennas for my new boat? You bet I am, just as soon as I can get Christmas paid off [img]/infopop/emoticons/icon_biggrin.gif[/img] [img]/infopop/emoticons/icon_biggrin.gif[/img] [img]/infopop/emoticons/icon_biggrin.gif[/img]

Am I going to get a combo antenna? I don't think so, I read Thom's disertation on antenna range in another thread (Thanks so much Thom [img]/infopop/emoticons/icon_smile.gif[/img]) and I am going for a seperate 8 foot VHF attatched to the top of my center consol grab rail.
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