[linux-dvb] [Fwd: RE: Some thoughts and questions]
abraham.manu at gmail.com
Sun Sep 30 08:26:27 CEST 2007
Fwd'd mail inlined.
Reply from one of the major broadcasters over here in the persian Gulf region.
So as the reply states, i was right additionally, alongwith Felix conclusion of the C band inversion.
In reality, we therefore have inversion due to
* I/Q wiring
* Flo > Frf
Does anybody have any different thoughts ?
-------- Original Message --------
Subject: RE: [linux-dvb] Some thoughts and questions
Date: Sun, 30 Sep 2007 09:56:53 +0400
From: Shaji Joseph <shaji at add.ae>
To: Manu Abraham <abraham.manu at gmail.com>
References: <46FE059F.1010907 at gmail.com> <46FE12D7.2080202 at elitedvb.net> <46FE1C02.5040703 at gmail.com> <46FE1F7C.40107 at elitedvb.net> <46FE256D.9070704 at gmail.com> <46FE26F8.4060800 at elitedvb.net> <46FE2EB6.2000403 at gmail.com> <46FE308B.1020401 at elitedvb.net> <46FE3806.4080206 at gmail.com>
In my understanding, Spectral inversion was done only on C band analogue
transmissions. And receivers used to have an option to select inversion
ON or OFF.
From: Manu Abraham [mailto:abraham.manu at gmail.com]
Sent: 29 September 2007 15:33
To: Shaji Joseph
Cc: Felix Domke
Subject: Re: [linux-dvb] Some thoughts and questions
Can you please enlighten us whether "broadcasters are required to send
as described in the rest of the mail, in case you have any idea on the
(We are talking about QPSK modulation/demodulation, according to college
books, as implemented by a broadcaster)
Felix Domke wrote:
>>>>>>> - Inversion might happen on up- and downconversion, depending
>>>>>>> frequency situation you have.
>>>>>>> - The SatelliteDeliverySystemDescriptor does not specify
>>>>>> 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
>>>> 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
> 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.
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