Thread: Inmarsat?

At the quite excellent Queanbeyan 4wd show yesterday, they were selling Isatphone Pro satellite phones for $749 outright. They had prepaid plans from $20 with 20 minutes talk time and 2 years to use the credit. A lot cheaper than a monthly and ideal for the casual user. Has anyone used the Inmarsat satellite? It's geocentric over New Guinea so obviously would be better the further north you go. Thinking of one for any remote desert travel I'm planning. Cheers

Originally Posted by goingbush

Yes, Ive used Inmarsat at work, Installed them as both interim phones & Payphones, then Telstra moved away from them for some reason,............................

Seems like we both used to work for the same mob. Was SH the boss at Healsville if you were there ?
The Inmarsat gear Telstra used was pretty good stuff. Can't remember the brand but it was Scandinavian made and top shelf.
Telstra went to iridium based stuff probably because it was a lot cheaper and used a non directional antenna so was easier install.
The technical difference between these was that Inmarsat used geosynchronous satellites, either POR (Pacific ocean region) or IOR (Indian ocean region), depending where in Australia you were, which required a directional antenna and transmitter capable of reaching 30,000 Km to the satellite wheras the iridium based satellites are polar orbiting LEO (low earth orbitting) satellites at a couple of hundred K's up. Non directional, lower powered and simpler antenna.
Both work well on voice but signal delay can be a bit of a problem with the geo sync. stuff, about 1/4 sec from memory which can be pretty ordinary for data. Signal delay makes two way conversation a bit difficult until you get used to it. You don't realise how much you tend to talk over each other on a telephone conversation till you've used a sat. phone.
Down here in Vic we used the POR satellite at approx. 5 degrees east of north and 30 degrees above the horizion (from memory), and as long as you could see this bit of sky it worked well. If you couldn't see this bit of sky or there were trees in the way it didn't work.
With iridium based stuff this wasn't a problem as the satellites travel from north to south and as the earth rotates you have a 'sunrise' and 'sunset' with the satellites. As you lose one you pick up the next and the call is passed on a bit like what happens with mobile cells. The downside is if you are in a north/south valley like Walhalla in Gippsland for example you lose one satellite before you pick up the next one and the call drops out.
In open areas (most of the outback) this is not a problem.
With the Inmarsat it was neccessary to dial the complete IDD number ie. 0011 61 3 59 428 111 to get to 0359 428111 (this isn't a real phone number).
With an iridium mobile you'd just dial the ten digit number. ie. 0359 428111.
With Inmarsat services replacing fixed phones dialling 000 became a major issue as Australian law states that the calling partys number must be passed forward to 000 so that address details can be determined. A complex process was completed at installation to replace the satellite number with a dummy local number so this could be achieved. Not a problem for mobile users but I've got no idea what happens if you dial 000 on an Inmarsat service. At best not enough digits to switch the call. Same with iridium, I've never tried.
It's a good idea to carry 'normal' (ten digit) emergency service phone numbers because of this.

Deano