[USRP-users] N210 WBX annoying spurs while switching

Matt Ettus matt at ettus.com
Thu Oct 23 01:52:10 EDT 2014


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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