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Old 21-03-2016, 15:17   #16
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Re: Sat Phone Vs Iridium Go!

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Originally Posted by N3VR L8 View Post
They weren't wrong, but in this scenario I don't think they were correct either.

If the GO were able to be placed somewhere truly free of obstructions on all sides the antenna would not garner any improvement.

With that said, I find it hard to believe this is the scenario on a vessel and agree with your sentiment. Having an antenna above sails, wheel houses, other electronics, etc etc etc would definitely be beneficial to maintaining a consistent signal to the satellite.
Well yeah, sure, if you have the right location the bar antenna is probably ok (it's been a long time since I worked for Moto on Iridium so I don't know the internal design of the Go). But I've never seen a sailboat where that was realistically the case, so where I've helped people install them I've always suggested using the external antenna.
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Old 21-03-2016, 16:13   #17
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Re: Sat Phone Vs Iridium Go!

LMR-400 is good stuff, but you have to remember that satcoms work on the fm capture effect. If the satellite can accommodate 100 simultaneous connections, then just like a cell phone tower, it will DROP YOURS is a stronger one comes along and it is already at capacity.


So it behooves the user to get the absolute maximum power out their antenna, and that means if you physically can use a lower-loss cable (like LM600 instead of LM400) then there's an absolute reason to use the best possible cable. Or perhaps, you've got the sail out, reaching, and it is in the line of sight between the antenna and a low satellite. What's the attenuation of a wet sail? On a rainy day?(G)


The lowest loss ("best") possible cable is always a good idea.
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Old 21-03-2016, 16:49   #18
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Re: Sat Phone Vs Iridium Go!

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LMR-400 is good stuff, but you have to remember that satcoms work on the fm capture effect. If the satellite can accommodate 100 simultaneous connections, then just like a cell phone tower, it will DROP YOURS is a stronger one comes along and it is already at capacity.


So it behooves the user to get the absolute maximum power out their antenna, and that means if you physically can use a lower-loss cable (like LM600 instead of LM400) then there's an absolute reason to use the best possible cable. Or perhaps, you've got the sail out, reaching, and it is in the line of sight between the antenna and a low satellite. What's the attenuation of a wet sail? On a rainy day?(G)


The lowest loss ("best") possible cable is always a good idea.
As far as I know each bird can handle ~1000 concurrent calls so it would be very rare for that to become an issue. Obviously some services, openport for example, will take priority to a standard voice session if such an instance were to occur. If they ever get NEXT up in the sky (first launches scheduled with SpaceX for this summer) this will become a virtually irrelevant topic

Recommendation is to stay under 3dB loss with a passive antenna, active antennas have their own required dB specs depending on manufacturer and hardware components. They are quite a bit more $$ but can handle virtually any run you throw at them with a far smaller diameter cable.

If an active antenna run won't do it (unlikely maritime scenario) you could look into something like an ASE ComCenter outdoors unit which would utilize a standard POTS line and give you up to ~8,000ft to play with.

Great discussion
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Old 21-03-2016, 17:35   #19
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Re: Sat Phone Vs Iridium Go!

"a standard POTS line and give you up to ~8,000ft to play with."
But that will only get you 1-1/2 miles offshore before the line snaps tight.(G)
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Old 21-03-2016, 18:27   #20
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Re: Sat Phone Vs Iridium Go!

Sat phone! do you mean inmarsat, geostationary all low latitude places covered.
This service as explained to me is far better than lowearth orbit of iridium, that is belting past at 1000's mph. I've seen delivery skippers really lose there cool over the flaky service.
I'm in Aus, inmarsat devices are being sold to vehicles going remote, the phone devise I know of is the "Inmarsat Isatphone 2", the modem devise is called "Wideye Isavi Isathub" heres a link that I picked from Google,

IsatHub Satellite WiFi Hotspot by Inmarsat | BlueCosmo

Both devises have there own sim card. I'm not saying there cheaper, but far better, got my info from a SAS soldier who was supplied with iridium devise in Afganistan not happy, also complained of dropouts when trying to co-ordinate military activities. Inmarsat worked far better, so he says.
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Old 21-03-2016, 19:49   #21
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Re: Sat Phone Vs Iridium Go!

Inmarsat is geostationary, correct. The satellites are 20k miles up which means the devices require pointing so something like an isathub will not work if you're underway.

I wouldn't say one network is any better than the other and iridium definitely isn't flaky by any means. Iridium is also truly global whereas inmarsat is not.

If you're keen to the isathub I'd recommend taking a look at the explorer 510.. a much more rugged and robust unit. The isavi/isathub is very cheaply made and will not take any abuse at all. As I mentioned these will require pointing to the satellite which isn't doable on a moving vessel.

Id also recommend doing some research on where inmarsat allows use of those services. If they see them offshore consistently they will likely shut them down because they aren't a maritime service and they'd much rather have you with a fleet broadband or fleetone system.

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Old 22-03-2016, 15:43   #22
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Re: Sat Phone Vs Iridium Go!

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As far as I know each bird can handle ~1000 concurrent calls so it would be very rare for that to become an issue. Obviously some services, openport for example, will take priority to a standard voice session if such an instance were to occur. If they ever get NEXT up in the sky (first launches scheduled with SpaceX for this summer) this will become a virtually irrelevant topic
That was certainly correct back in the day, and I'd assume any software improvements since would have only made it better. I highly doubt you'd ever lose a call due to capacity. The system doesn't prioritize higher power signals over lower anyway - as long as there's connectivity it's first come first served.

There are two normal drop modes for Iridium: Low signal between the phone and satellite, and loss of inter-satellite signal. Iridium satellites connect to each other to route calls between phones and ground stations, so out over the middle of the ocean you potentially have many satellite-satellite hops to get to a ground station. Lose any one of those and the call drops. Iridium uses polar-ish orbits so on average the point where they're farthest apart is the equator, which is where the probability of losing a satellite-satellite link is highest.

Bottom line: Do your best to make sure your phone-satellite connection is as good as possible since that's the most common call drop problem. But be aware that the closer you get to the equator the less reliable it gets in general.
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Old 22-03-2016, 18:00   #23
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Re: Sat Phone Vs Iridium Go!

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That was certainly correct back in the day, and I'd assume any software improvements since would have only made it better. I highly doubt you'd ever lose a call due to capacity. The system doesn't prioritize higher power signals over lower anyway - as long as there's connectivity it's first come first served.

There are two normal drop modes for Iridium: Low signal between the phone and satellite, and loss of inter-satellite signal. Iridium satellites connect to each other to route calls between phones and ground stations, so out over the middle of the ocean you potentially have many satellite-satellite hops to get to a ground station. Lose any one of those and the call drops. Iridium uses polar-ish orbits so on average the point where they're farthest apart is the equator, which is where the probability of losing a satellite-satellite link is highest.

Bottom line: Do your best to make sure your phone-satellite connection is as good as possible since that's the most common call drop problem. But be aware that the closer you get to the equator the less reliable it gets in general.
Spot on!

I will add that not all of the birds are equal in terms of performance these days.. gotta remember these things are ~5 yrs beyond life expectancy.

Excited to see NEXT to say the least, it should vastly improve an already solid network.
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Old 22-03-2016, 18:22   #24
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Re: Sat Phone Vs Iridium Go!

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Spot on!

I will add that not all of the birds are equal in terms of performance these days.. gotta remember these things are ~5 yrs beyond life expectancy.

Excited to see NEXT to say the least, it should vastly improve an already solid network.
Yeah, good point about the age of those things. I left Moto 20 years ago and the satellites were all launching the year or two after that I think. NEXT will bring a lot of new capabilities from what I've read, and should start giving the newer Inmarsat systems more of a run for their money.
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Old 22-03-2016, 18:22   #25
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Re: Sat Phone Vs Iridium Go!

AFAIK they are all still FM systems, and all FM systems suffer from the "capture effect". No matter how they are programmed, they will still drop a weaker signal when a stronger one "captures" the radio.


Capacity may be plentiful, but as they proved even with land-based systems after Katrina and Wilma, it is indeed possible to consume the entire capacity of a satellite. That's one reason why Inmarsat (and others) had contracted to launch more satellites--which have been substantially delayed by launch failures. The folks who own 'em and sell capacity on 'em, are spending many millions to add more capacity.


Will there be a crowd 1000 miles offshore? One hopes not. But as that call gets passed off to other satellites, looking for earth stations...there's a bottleneck too.


Heck, even the domestic landline telephone systems and the cellular systems run out of capacity on Mother's Day.
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Old 22-03-2016, 18:34   #26
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Re: Sat Phone Vs Iridium Go!

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What are the differences between a Sat Phone Vs Iridium Go!?
As far as I am aware you can make calls from both and access internet from both. (Not for browsing of course).

What are peoples views on each system? pros / cons etc?
I'm trying to decide which way to go.

Thanks.
Satcom math is still a hard nut to crack.

I'm loving our SSB, Pactor and Sailmail account. Gribs, emails and facebook posts and tweets sent in the emails to a land based assistant.


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Old 22-03-2016, 20:45   #27
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Re: Sat Phone Vs Iridium Go!

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AFAIK they are all still FM systems, and all FM systems suffer from the "capture effect". No matter how they are programmed, they will still drop a weaker signal when a stronger one "captures" the radio.
Not as much as you might think, at least in the case of a digitally modulated system like Iridium. Amplitude near-far is much more of a problem in analog systems. Systems that use PSK modulation are typically very resistant to the capture problem assuming the receiver is designed right. This is shown to be made significantly better if you use PSK with TDMA or other "start-stop" type channel patterns.

Iridium uses QPSK modulation in both directions for all the traffic channels inside a 4 timeslot TDMA frame structure. Carrier modulation is of course FM. Bandwidth is very narrow (41.67 kHz) with a nominal (0 dBm) 2.5 kHz dead air spacing between the carriers. There are 240 carriers. To keep adjacent channel interference low and make the filters easy (hence reducing the capture problem further) each spot beam uses 40 carriers, so frequency reuse across the spot beams (essentially the cells) is N=6, which is much better than the typical N=3 most cellular systems use.

In practice (with the current satellites - I have no idea how the new ones are being done) each channel has an independent receiver at the satellite with a very high rejection bandpass filter tuned to the center frequency, followed by analog FM demod, the A/D, digital filtering, and then digital QPSK demod, all of which results in excellent adjacent channel and timeslot rejection and hence almost no capture problem. That is made easier because there's no such thing as a strong signal at the satellite - best case is probably -90 dBm or so, with a noise floor around -114, so the wave forms are quite narrow and widely spaced at the satellite. Right from the start almost all the problems we saw were simple fading because the signal is so weak at the satellite and there are so many atmospheric effects that attenuate it further. Well, that at the inter-satellite microwave links (which are a completely separate beast).
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