[USRP-users] N210 WBX annoying spurs while switching

Marcus D. Leech mleech at ripnet.com
Wed Oct 22 14:03:57 EDT 2014

On 10/22/2014 12:16 PM, Matt Ettus via USRP-users 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
Even ignoring the digital bits (ramp-up/ramp-down), when you turn a TX 
on/off abruptly, there'll be some spectral anomalies, for the same 
reason, but
   in the analog domain, and usually weaker.  In commercial 
for-a-particular-purpose radio, there are TX filters to prevent such 
transients from
   being too strong out-of-band.  In a not-for-a-particular-purpose 
radio, such as an SDR, no such filtering can be provided.

Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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