SatSig topic:

.90 m transmit dish - link budget question

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Aug 10^th, 2006 at 10:26pm

I'm wondering if any one knows if a .90m dish with 4 Watt BUC on Intelsat 8 Here in the U.S will be capable of upload speeds of .768 or if I have to go with the 1.2 meter dish. This is for a Mobile application and due to price constraints I would like to use the .90 Meter dish. If anyone has tested this out or knows someone who has any help would be appreciated. Thanks

Aug 11^th, 2006 at 6:48am

look at the footprint maps of the bird you are going to use

i expect such a question from an end-user, don't you have a (real) tech there ??

Aug 11^th, 2006 at 10:44am

Get the footprint maps and find the uplink G/T and PFDsat contours over the proposed site(s). While you are at it also get the downlink EIRP contour map towards the large hub site. Ask INTELSAT for the nominal operating point for multicarrier operation in that transponder (back off in and back off out). Note that the PFDsat figure may be different from one transponder to another to suit the type of traffic (single or multicarrier). Note the share of the bandwidth of your carrier versus the transponder bandwidth.

Using the above, calculate your share of the transponder operating uplink pfd that is yours. Then use a link budget and adjust your uplink power (0.9m + up to 4 watts) to generate an appropriate uplink pfd. If you can do that with 0.9m and 4 watts then your uplink is adequate.

Now work out your share of the transponder operating downlink eirp. Do a link budget into the large hub dish. Add the up and down C/Ns together to see if the total C/N is adequate at the hub receive modem, allowing a margin for rain fading.

My link budget calculator at https://www.satsig.net/linkbugt.htm may be of help but you are better to make up your own spreadsheet to do it just the way you want.

Best regards, Eric.
wxw

Aug 12^th, 2006 at 3:54am

Nice tables Eric, that saves a lot of wotk

Aug 12^th, 2006 at 8:30pm

I have found that calculations (especially in the Satellite world) only means so much. Eric, I really appreciate your response. We have done the calculations, (dunhill), what I was hoping for, and perhaps I should have been more specific was a response from someone who has done an actual test. A real life trial. I normally would not even consider going to a .90 Meter dish for this service, but I was looking to keep the price lower for a customer. I guesse I will just have to purchase a .90 meter and do the testing myself. Thanks for your responses. -even the sarcastic ones.

Aug 13^th, 2006 at 12:02pm

Try the uplink calculation alone. Put in 14 GHz, 0.9m, 4 watts, 600000 Hz bandwidth and 0 dBK G/T and the result is C/N=10.3 dB.

If the downlink is similar you are looking at C/N=7 dB overall. Above threshold, but hardly comfortable.

The uplink G/T towards the transmit site matters. I just guessed 0 dBK above. The transponder gain setting also important plus the downlink hub dish size.

Do choose a dish and matching feed intended for transmit operation with a contractually specified tx gain.

Best regards, Eric.