Hello Everyone,
I'm new to this forum, so please accept my greetings.

I would like someone's opinion about the following situation. We have onboard our boat an Idirect 3100 series modem, connected to a Seatel 4003 dish. When we lose the satellite signal and therefore the connection, due to mast obstructions etc,  
it takes sometimes up to 15-20 minutes to get the link back. We've heard that some Providers do this much quicker. Someone also told me that to resolve this problem it should be possible to insert a sentence in the options file to tell, for example, the modem to take the position from the embedded GPS every few seconds and not from an external GPS source. This time lag to resume the link should be brought down to 2-3 minutes under optimal conditions.

What do you think?
Thanks for your kind attention.
Giancarlo.

Do you know if your upstreams are being spread? i.e. spread spectrum?

How would I find this out? Unfortunately I've never heard of the spread spectrum........
Thanks.

Most "Satellite On the Move" applications utilize spread spectrum to avoid adjacent satellite interference (ASI).

Now that I have re-read your post, you stated that you are using a 3100 Series iDirect unit.  That unit does not support spreading, so we have the answer.  

What is the size of your downstream carrier (MHz?  Info rate?  Symbol rate?). Do you have a copy of your options file?  If so, under the block [MODEM_PARAMETERS] there is a rx_bitrate...what are those values?  You can also telnet to the unit and type rx bitrate at the prompt, and it will spit out the digits.

What type of LNB are you using on that stabilized 4003 parabolic? NJR PLL?

When you say you are using an external GPS, how is it connected to the Seatel or the iDirect unit (read: how are you feeding NMEA to the iDirect)?  Is it provided on console or is it provided via telnet session?  I cant remember with the Seatel units.

Bottomline: 15-20 minutes is way to long for re-acquisition.  You should be seeing no more than 1 minute before reacquiring the network.  Your problem is either with the stability of your LNB or the way your unit takes in GPS (as you mentioned).  I would work it from those two angles.  If your LNB is a PLL, and confirmed good, then you can almost rule that out.  

What is the look angle (elevation)? Version option file?

Have you confirmed the signal strength with your provider? Also, with your provider on the phone, reset the modem and find out what the hub is seeing on their side as the modem tries to come back into the network.