[linux-dvb] [Fwd: RE: Some thoughts and questions]

Manu Abraham abraham.manu at gmail.com
Sun Sep 30 08:26:27 CEST 2007


Felix Hi,

Fwd'd mail inlined.

Reply from one of the major broadcasters over here in the persian Gulf region.

http://www.adduniverse.com

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 ?

Regards,
Manu

 
-------- 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.

Regards
Shaji Joseph


-----Original Message-----
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

Dear Shaji,

Can you please enlighten us whether "broadcasters are required to send
non-inverted signals"
as described in the rest of the mail, in case you have any idea on the
same.

(We are talking about QPSK modulation/demodulation, according to college
books, as implemented by a broadcaster)

Regards,
Manu


Felix Domke wrote:
> 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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