[USRP-users] N210 WBX annoying spurs while switching

bob wole bnwole at gmail.com
Thu Oct 23 02:06:49 EDT 2014


Okay, I'll make a custom block in gnruadio to achieve ramp up/down for FSK
waveform to avoid "keyclicks" .

On Thu, Oct 23, 2014 at 10:52 AM, Matt Ettus <matt at ettus.com> wrote:

>
> No problem.  The RF filter at the output really isn't the proper way to
> solve this problem, it will just keep the noise within a band.  What you
> really want is to avoid putting out energy outside of your channel, and
> that can only be done with ramping.
>
> Matt
>
> On Wed, Oct 22, 2014 at 10:46 PM, bob wole <bnwole at gmail.com> wrote:
>
>> Thanks Matt for your response, that is the exact answer I was looking
>> for. Actually I am using USRPs for TDMA and I do not want my time slot to
>> increase very much. I wanted to know the ramping duration because this will
>> affect the time slot duration. Second option could be that I can add an RF
>> filter at the output of USRPs.
>>
>> On Thu, Oct 23, 2014 at 10:25 AM, Matt Ettus <matt at ettus.com> wrote:
>>
>>>
>>> Yes, but it is even better to ramp up at the beginning and down at the
>>> end, and then pad a little bit with zeros.   If you ramp up and down
>>> smoothly for 1us, you'll confine the emissions to about 1 MHz on either
>>> side.  All bursty communication systems will do this, like Bluetooth, Wifi,
>>> even morse code, and most newer standards even specify the ramping rate.
>>>
>>> Matt
>>>
>>>
>>> On Wed, Oct 22, 2014 at 10:08 PM, bob wole <bnwole at gmail.com> wrote:
>>>
>>>> So you are suggesting that I should zero pad samples at start and end
>>>> of my burst to avoid this ?
>>>>
>>>> On Wed, Oct 22, 2014 at 9:16 PM, Matt Ettus <matt at ettus.com> wrote:
>>>>
>>>>>
>>>>> When you start and stop transmission without smoothly ramping the
>>>>> signal to zero at the beginning and end, you will create wideband spurs.
>>>>> Just think about it as amplitude modulation.  Even if you are transmitting
>>>>> a pure sine wave, if you turn it on and off quickly, it will create out of
>>>>> band spurs.  Hams call this keyclicks.
>>>>>
>>>>> Matt
>>>>>
>>>>>
>>>>> On Wed, Oct 22, 2014 at 1:25 AM, bob wole via USRP-users <
>>>>> usrp-users at lists.ettus.com> wrote:
>>>>>
>>>>>> I noticed that there are a lot of significant spurs generated in the
>>>>>> output of WBX, on different frequencies randomly, when I use tx_time,
>>>>>> tx_sob_tx_eob tags. I do not see these spurs if I transmit continuously.
>>>>>> These spurs appears only when I start and stop transmission using stream
>>>>>> tags.
>>>>>> How can I get rid of these spurs and what is the cause?
>>>>>>
>>>>>> -
>>>>>> Bob
>>>>>>
>>>>>> _______________________________________________
>>>>>> USRP-users mailing list
>>>>>> USRP-users at lists.ettus.com
>>>>>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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