[linux-dvb] Some thoughts and questions

Felix Domke tmbinc at elitedvb.net
Sat Sep 29 13:01:31 CEST 2007


Hi,

>>>>>>  - Inversion might happen on up- and downconversion, depending on what
>>>>>> frequency situation you have.
>>>>>>  - The SatelliteDeliverySystemDescriptor does not specify Inversion.
>>>>> AFAICS, Inversion isn't a part of the transport.
>>>> Why not? It's part of it like the frequency, isn't it? 
>>> What i meant is that it does not depend on the transport, but the hardware.
>>> LNB + tuner <-> demod wiring
>>> Whereas frequency is not.
>> Some transponders have an inversed frequency spectrum already when
>> broadcasted (before downconversion).
>> There is no way for the broadcaster to specify this.
> What do you mean by a inverted spectrum when broadcast ?
> AFAICS, Inversion happens after there is a Phase shift to extract the I and Q signals
Swapping I/Q is *one* way to create spectral inversion. Just inverting
the spectrum is (obviosly) another one, and can happen on the
(non-complex) modulated signal as well. Just mix it with another
frequency and take the lower sideband.

It's the same thing which happens in a C-Band downconversion - it can
also happen in the upconversion.

I don't know if broadcasters are required to send non-inverted signals.
I just know (read: remember) that some do. I might be wrong, so second
opinions are welcome.

Again, I'm not a frontend guy. Maybe somebody with broadcasting
experiences can tell us more here.

Felix



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