A 2.4GHz to 1.5 GHz down converter
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>Its working!
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>Cool,
>now tune the sat receiver to 10,600,000,000 Hz higher because it assumes a LNB LO, makes 12041,474,000 Hz, we should see a signal:
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>indeed, and recording works too.
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>It is not completely clean as the other sat receiver shows (that one one has lock problems on this):
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>look at the constellation, that should be 4 dots at right angles...
>Looks like some noise, will have to find if it is the transmitter or the down converter, or both,
>what causes it, maybe decoupling;
As the LO in the down converter is clearly stable, as this picture shows:
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the instability in the QAM constellation must originate in the transmitter. As the transmitter is OK at 1.5 GHz, it must be in the new 2.4 GHz VCO, or its supporting circuits.
Spend some time doing measurements and indeed the VCO is a bit of a proximity detector, carrier changes some kHz if you put your hand close to the VCO output coax, maybe it needs a cleaner supply too. Looks like I need a buffer amp (MMIC) at 2.4 GHz, and perhaps even put that VCO in a separate shielded box, or put it closer to the QAM modulator (but there is no place there, well, maybe on top of it. Now there is an idea), anyways found several 2.4 GHz MMIC chips on ebay. Will think about howtodoit, it is not 2016 yet. But problem located, next step.