[USRP-users] N210 WBX annoying spurs while switching

bob wole bnwole at gmail.com
Thu Oct 23 01:46:00 EDT 2014


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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