Re: [Discuss-gnuradio] DAB with GNU Radio

[Martin Dvh]

Christoph Fischer wrote:
> Hello Andreas,
> 
> thank you for your very interesting reply.
> 
>>> we would like to implement a DAB receiver with GNU radio. On the
>>> hardware side we have a USRP with the TVRX daughterboard. 
>>
>> Jens Elsner, who worked on DAB some time ago, found out that the TVRX
>> actually disturbs the OFDM signal very much, making it rather hard to
>> receive DAB, so I would strongly discourage its use (I'm not able to get
>> any information out of TVRX samples currently).
> 
> That is bad news... So perhaps at first we should do some analysis if
> DAB is really impossible with the TVRX or if we only have severe
> degradation of SNR. We have a DAB transmitter just some km away from the
> university so perhaps it could somehow work at least for this one...
> Does anyone already have some data about the phase stability of the
> TVRX? Unfortunately the L-Band is no option here.

You could try undersampling with basicRX.
Frequency stability wouldn't be an issue. But the sensitivity is very very low 
and you get interference from all bands above 32 Mhz folded over
each other.

This could be improved by using a bandfilter and an amplifier in front of the 
basicRX.
Just use a bandfilter which only passes the part of band III which you are 
interested in.
The bandfilter should have a bandwidth of 30 Mhz or less.
For example 170 - 200 Mhz.

For amplification best would be a dedicated amplifier for this freq-band with 
20 to 50 dB gain.
But to keep things simple you could use an off-the-shelf amplifier for 
TV-signals which have usually 10 to 15 dB gain.

As an antenna you could use a home-made vertical dipole or J-antenna for 
exactly the right freq.
This also improves selectivity.

greetings,
Martin

>>> Is there any initial advice or pointers to existing implementations
>>> you could give us? Do we need the checkout the svn version or even
>>> some branch or is the 'latest stable' enough?
>>>
>>
>> I have uploaded my current code to [2]. It requires GNU Radio from the
>> trunk and some small patches (mainly for the peak detector). If you are
>> interested, I can also send you my mostly-finished semester thesis
>> off-list.
> 
> Thank you very much for all that. We also would be very interested in
> your thesis.
> 
> Regards,
> Chris
> 
> 
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