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VSAT technology and installation >> iDirect Forum: hubs and terminals >> 6mbps / 6mbps link ..

Message started by wbailey on Sep 22nd, 2009 at 9:51pm

Title: 6mbps / 6mbps link ..
Post by wbailey on Sep 22nd, 2009 at 9:51pm
Has anyone achieved a 6mbps/6mbps on any Ku Band iDirect? If so.. what was the smallest dish and buc you were able to get away with?? (I don't care about link budgets or off center of beam)

Just wanting to get a feel on what people are able to use to close this type of link :)

Title: Re: 6mbps / 6mbps link ..
Post by Eric Johnston on Sep 23rd, 2009 at 1:32pm
I don't know about the capability of an iDirect  to support 6 Mbit/s transmit, but be aware that the modem internal processing power may limit the useable bit rate below the stated maximum quoted rate. see

Regarding the satellite link, you do really need to consider the link budget and sidelobe interference limits.   What satellite beams ?  A C band global beam is far different from small Ka band spot beam.  What size dish is at the other end ?  A large 10m teleport dish is rather different from a 1.2m VSAT at the far end.

If you want some figures, as examples, I suggest..
11 watt BUC and 2.4m dish
20 watt BUC and 1.8m dish
45 watt BUC and 1.2m dish

Far more or far less may be needed for your particular example.

Best regards, Eric.

Title: Re: 6mbps / 6mbps link ..
Post by wbailey on Sep 27th, 2009 at 12:31am

I appreciate your response. We are running a 9 meter Ku band at our Earth Station. The remotes are typically 1.8m with 2-4 (sometimes 8 watt) BUC's. This 6mb/6mb link would most likely be a 1.8 with an 8-12 watt BUC. We're right in the center of the beam (at about 46db) so I was thinking 12 watt would probably clear it. Also, I probably neglected to mention I'm going to put this on my new Ku S2 network.

Title: Re: 6mbps / 6mbps link ..
Post by Eric Johnston on Sep 27th, 2009 at 2:58pm
If you already have a system that is operating well, with an acceptable rain fade margin then you can scale up the BUC output power with the bit rate increase.

If your BUC output power is now 1 watt for 500 kbit/s then
1M needs 2 watt.
6M needs 12 watt.

Be very careful with higher power BUCs.
1. The power supply and power supply cable need attention.  Higher voltages e.g. 36V DC or 48V DC have less voltage drop in the cables due to lower current. INFINITI 7000, for example, have a 48V option for 16W BUCs.
2. Be very careful not to exceed the drive level needed for P-1dB, as damage is likely.  Use BUCs with power output monitoring, power overload protection, temperature alarms and mute on LO fail  if possible. Some modems (I don't know about iDirect) will deal with FSK telemetry from the BUC.
3. If you want 8-PSK or 16-QAM, double the nominal rating so you operate at or below the P-4dB point to minimise distortion.
4. Higher power BUCs are seriously dangerous. Make sure no one can get near the feed output as it will cook your eye lens in a flash. Radio regulations say that all VSAT remotes must automatically go to transmit mute (inhibit, tx=off) if the receive path is blocked, but don't rely on that for safety.

Best regards, Eric.

Title: Re: 6mbps / 6mbps link ..
Post by wbailey on Sep 30th, 2009 at 6:47am
Mike was right, you are a ninja Eric.. LOL

Title: Re: 6mbps / 6mbps link ..
Post by TDMAMike on Sep 30th, 2009 at 12:53pm
I told ya.  If you want to know ANYTHING RF related, Eric is the guy to ask.

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