DaDogs
Semper Vigilantis
Premium
join:2004-02-28
Deltaville, VA
| reply to FightingBlue
Re: All well and good, but
said by FightingBlue:
What kind of requirements would there be for this tech? What kind of antenna would you require to get a signal? Half the point of wireless internet is the efforts to make it mobile, and that can't happen if you have a 2-foot antenna to carry around.
You have never seen the antenna on a Walkman have you? There will be no 2' antenna.
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Pictor Guy
join:2004-06-21
Sammamish, WA
| said by DaDogs  :You have never seen the antenna on a Walkman have you? There will be no 2' antenna.
Actually yes.  And, many 'walkmans' used the head phones as part of the antenna. Anyway... the site claims that they will be using UHF and VHF for this. If that's the case the antenna would be around 6" (give or take) for UHF. Larger for VHF. Higher frequencies need smaller antennas to be equally efficient. Next time you see a car with an XM or Sirius radio antenna and a standard FM/AM antenna compare the size of the two. But there is also missleading information on the site... "Because the propagation characteristics of low frequencies allow them to pass through dense obstacles, deployment of xMax in the VHF and UHF bands completely eliminates the line of sight issues that are problematic with higher frequency broadband technologies. "UHF is VERY line of sight. While it will penetrate some buildings better than something in the 2.4GHz ISM band it's still line of sight. And to a lesser extent VHF is also line of sight. Just ask a boater how far over the horizon they can xmit on their VHF radio. Now if xMax is going to use HF signals then it wouldn't have to be line of sight but now you're talking HUGE antennas.  |
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DaDogs
Semper Vigilantis
Premium
join:2004-02-28
Deltaville, VA
1 edit | said by Pictor Guy :Actually yes. And, many 'walkmans' used the head phones as part of the antenna. Then you realize that was an FM antenna for ~100 MHz, that would be VHF actually LVHF... Ever see a bar antenna for AM broadcast band? Doesn't have to be very efficient given the wave lengths involved in transmitting GROUNDWAVE for a couple of hundred miles, does it?
said by Pictor Guy :Anyway... the site claims that they will be using UHF and VHF for this. Yes it does. It also suggests they can do it anywhere in the spectrum.
said by Pictor Guy : If that's the case the antenna would be around 6" (give or take) for UHF. Larger for VHF. Higher frequencies need smaller antennas to be equally efficient. Really, interesting So if I made a quaterwave marconi for 10 meters (LVHF) it would be roughly 2.5 meters tall? And if I made the same kind of antenna for 3 GHz (UUHF) it would be roughly 2.5 CM tall? Cool.
said by Pictor Guy : Next time you see a car with an XM or Sirius radio antenna and a standard FM/AM antenna compare the size of the two. I'll do that.
said by Pictor Guy : But there is also missleading information on the site... "Because the propagation characteristics of low frequencies allow them to pass through dense obstacles, deployment of xMax in the VHF and UHF bands completely eliminates the line of sight issues that are problematic with higher frequency broadband technologies. "UHF is VERY line of sight. While it will penetrate some buildings better than something in the 2.4GHz ISM band it's still line of sight. And to a lesser extent VHF is also line of sight. Like 100 MHz VHF? Like Channel 2 TV, VHF? That kind of LOS? Yep, you are right these frequencies VHF and UHF are considered LOS and they are more readily absorbed by trees and there are more reflectors in the environment at these frequencies. What you are failing to understand is the fact that ANY electromagnetic emission exists and radiates forever. It may exhibit path losses to the point that it is below the ambient temperature of the universe but it is still there, still expanding outward. It is merely undetectable below the noise floor. Now the noise floor is an interesting phenomena, you see what "seems" to be a hard line isn't a hard line at all. At any given point in the spectrum any instantaneous reading of signal strength will vary significantly from any other time separated reading of signal strength at that frequency. This means that given sufficient receive sensitivity one can detect data below the , admittedly arbitrary, "noise floor", if one but knows when, where, and what signal level, to look for... but you obviously knew that.
said by Pictor Guy : Just ask a boater how far over the horizon they can xmit on their VHF radio. Now if xMax is going to use HF signals then it wouldn't have to be line of sight but now you're talking HUGE antennas. I have a better idea. Since we are getting "technical" here. Have a look at this web site »home.cogeco.ca/~dxinfo/tropo.html , then you tell me if I can reach the Bahamas from Charlestown, SC on 144 MHz today? All marine operators on Marine VHF can reach WELL beyond the horizon because of a layer of super saturated air which is always present near the surface of the ocean. Ducting at VHF is always present on the ocean.
Regarding HF antennas ... See my comments regarding portable antennas for AM band ...
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BosstonesOwn
join:2002-12-15
Everett, MA
clubs:
 ·Comcast
| Out of curiosity exactly how far can a vhf wave travel ? I just bought a new boat and it has a vhf radio with the gps beacon signal tied in. I am sort of curious of exactly how far that sucker can broadcast.
Ok back on topic after the answer
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Pictor Guy
join:2004-06-21
Sammamish, WA
1 edit | said by BosstonesOwn :Out of curiosity exactly how far can a vhf wave travel ? I just bought a new boat and it has a vhf radio with the gps beacon signal tied in. I am sort of curious of exactly how far that sucker can broadcast. Ok back on topic after the answer Based on my experience and what most people will tell you at the USPS or USCG it's about 15 miles ship to ship but can be as much as 50 miles if both antennas are high enough. See... »www.yachtcom.co.uk/comms/
But alot of it has to do with the height of the antenna and sea conditions (rolling the ship/antenna).
\\\\edit
Here's more from the USCG...
»www.navcen.uscg.gov/marcomms/boater.htm
"Your VHF radio is intended mainly for short range communications, generally 5-10 miles, and at least 20 miles to a USCG station. To communicate at longer ranges, you will normally need a satellite telephone or an MF/HF marine radiotelephone. Marine radiotelephone equipment normally operates between 2 - 26 MHz using single sideband emissions. MF/HF marine radiotelephones can also be used to receive high seas weather broadcasts, and by using a computer and a special interface provided by some coast stations, can provide Internet email." |
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DaDogs
Semper Vigilantis
Premium
join:2004-02-28
Deltaville, VA
| reply to BosstonesOwn
said by BosstonesOwn :Out of curiosity exactly how far can a vhf wave travel ? I just bought a new boat and it has a vhf radio with the gps beacon signal tied in. I am sort of curious of exactly how far that sucker can broadcast. Ok back on topic after the answer The reason they tell you the numbers they tell you is because planning must be absolute. If you want to calculate your range with VHF just figure the using this link:
»www.qsl.net/w4sat/horizon.htm
This as I said is because safety is an issue. The truth is your range will nearly always be greater than that returned by that calculator over water because ducting is very common over water. It is nearly always present.
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BosstonesOwn
join:2002-12-15
Everett, MA
clubs:
·Comcast
| said by DaDogs :said by BosstonesOwn :Out of curiosity exactly how far can a vhf wave travel ? I just bought a new boat and it has a vhf radio with the gps beacon signal tied in. I am sort of curious of exactly how far that sucker can broadcast. Ok back on topic after the answer The reason they tell you the numbers they tell you is because planning must be absolute. If you want to calculate your range with VHF just figure the using this link: » www.qsl.net/w4sat/horizon.htmThis as I said is because safety is an issue. The truth is your range will nearly always be greater than that returned by that calculator over water because ducting is very common over water. It is nearly always present. Neat they told us 7 miles max. From the high of the antenna to the water is 15 feet on #1 and 12 on #2 , really interesting I have never dealt with vhf before. I usually carry a sat phone from work. But it looks like im in the market for a nice vhf antenna that may be telescopic
You learn something new every day.
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"It's always funny until someone gets hurt......and then it's absolutely friggin' hysterical!" |
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