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VSAT technology and installation >> LinkStar Forum: VSAT hubs and terminals >> need help: Combining and Converting L/IF bands

Message started by MCI on Aug 24th, 2011 at 1:32am

Title: need help: Combining and Converting L/IF bands
Post by MCI on Aug 24th, 2011 at 1:32am
Hello Forum;

I need help and guidance please.

I a teting an IP SNG system on two different satellites using two different uplink systems.

The IP SNG system hub carrier has a modulator with an L band output
The first Test:
-Using a flyaway system; with an Encoder/modulator with an L band output. I will require to combine both modulators (the hub carrier modulator and the flyway modulator) L band outputs to feed the flyway Upconverter with a balanced L band input.

I plan to use R&K PD610-0S combiner

Is this a good enough a product?

The second Test:
-Using a 3.8M fixed uplink station. The station modulator has an IF band output that feeds an IF input upconverter. To combine the Hub carrier modulator (which has an L band output) I will need to;
1- convert the hub carrier modulator from L to IF band.
2- Combine both the station modulator IF output and the converted hub carrier modulator (from L to IF band) into a balanced IF stream to feed the station upconverter.

My question;
-is there a product that perform the L-IF conversion as well as perform the two IF signals combining? or do I have to use to different products? If so can you recommend which one(s)?

Many thanks for your help here.  

Title: Re: need help: Combining and Converting L/IF band
Post by Luchsinger on Oct 6th, 2011 at 3:46pm
L-Band is an IF frequency (in the satellite world).  If I am right in presuming you meant (VHF) 70 or 140Mhz then there is a bunch of those converters.

I have seen people connect the TX of their L-Band modems to their upconverters which would output the VHF 70/140Mhz frequencies.  And vice versa on the down side.

In regards to the combination with the previously mentioned conversion; I am not aware of any devices that do that, sorry.

Title: Re: need help: Combining and Converting L/IF band
Post by Eric Johnston on Oct 6th, 2011 at 7:19pm
In the case of test 1 above...

Regarding two modulators simultaneously connected you need to be aware that this will cause really bad intermodulation interferences to other services if the BUC is not backed off a long way, like -3 dB or more.  BUCs are normally operated with one carrier near maximum output level.   It you put two carriers through you need a BUC rated at least four times as powerful as one carrier.  e.g. Two 20W carriers through a 100W BUC, instead of one 20W carrier thtrough a 25W BUC.  Even then you must have a spectrum analyser coupled from the waveguide output to the feed to measure the intermod levels, plot them and get then approved by the satellite operator.

In the case of test 2 above...

The same applies, regarding intermodulation, if the output of two upconverters are merged before feeding an HPA.

Best regards, Eric.

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