Replica outband

GNU Radio
1

Hi all,
I’m transmitting my signal with 5Mhz bandwidth with a carrier of 70Mhz,
analyzing output spectrum I see some “replicas” outside the bandwidth
(see attached image).
I’m using a WBX, will the uhd::usrp::multi_usrp::set_tx_bandwidth remove
those
replicas? I don’t see any filter after the I/Q modulator (ADL5386).

Is this intended ?

Regards

2

On 07/28/2011 02:58 AM, Gaetano M. wrote:

Hi all,
I’m transmitting my signal with 5Mhz bandwidth with a carrier of 70Mhz,
analyzing output spectrum I see some “replicas” outside the bandwidth
(see attached image).
I’m using a WBX, will the uhd::usrp::multi_usrp::set_tx_bandwidth remove those
replicas? I don’t see any filter after the I/Q modulator (ADL5386).

Is this intended ?

Those are odd harmonics, which are expected. In any application where
you are transmitting over the air with significant power, you will need
to filter out the odd-order harmonics.

The WBX has such wide frequency coverage that it is impractical to have
enough filters to do this for the whole range. This is why we have the
grand-daughterboard – you can either modify the filter on there
(minicircuits has a whole range of filters to cover the band), or make a
custom filter board for your specific needs.

Matt

3

On Thu, Jul 28, 2011 at 6:02 PM, Matt E. [email protected] wrote:

Those are odd harmonics, which are expected. In any application where
you are transmitting over the air with significant power, you will need
to filter out the odd-order harmonics.

The WBX has such wide frequency coverage that it is impractical to have
enough filters to do this for the whole range. This is why we have the
grand-daughterboard – you can either modify the filter on there
(minicircuits has a whole range of filters to cover the band), or make a
custom filter board for your specific needs.

Thank you for the explanation, I did immagine that seeing that there is
no
filter after the I/Q modulator I did ask just to be sure.

Regards
Gaetano

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