I am confident you guys will find the ' silver bullet '.....for noise... 73, w5xz, dan
--- On Mon, 5/30/11, Bob McGwier <[email protected]> wrote: From: Bob McGwier <[email protected]> Subject: Re: [FlexEdge] Noise Blanker Question To: "Brian Lloyd" <[email protected]> Cc: "Kerry Miller" <[email protected]>, [email protected] Date: Monday, May 30, 2011, 1:45 PM Noise pulses are short in duration EXCEPT after you pass them through the bandpass filter and then they map out the impulse response of the filter convolved with the pulse shape as received. No pulse is a dirac delta (single spike with its energy spread out to infinity in frequency). However, you constantly hear stuff about roofing filters for the noise blanker. There is a way to achieve the DSP equivalent of this. It is achievable in software and it works better than a roofing filter because its action is CONCENTRATE ON THE PULSE REGION. It can be done BEFORE the pulse has been stretched out by the filter. So there are multiple sides to this problem. 1) Detection of the pulses with high probability of finding them, and low probability of misidentifying them. 2 Register the pulse location in time, its amplitude and phase components that are relevant to any processing to be done 3) Algorithm to suppress the impact of the registered pulse. It is on the software list to implement with no firm delivery date for now, so no promised estimated time of arrival is intended or implied. Bob On Sun, May 29, 2011 at 4:27 PM, Brian Lloyd <[email protected]> wrote: > On Sun, May 29, 2011 at 4:17 PM, Kerry Miller <[email protected]> wrote: > > > Here's my question. Since the NB is really done in software on the Flex, > > is > > there a way to have a noise blanker (NB3 maybe?) that ONLY works inside > the > > passband of the filter? If it was possible to do this maybe it would > > eliminate the noise (like my perpetual powerline noise) inside the > filter's > > passband but not be affected by the strong signals outside of the > passband. > > > > It is not a bad idea but it does help to understand how a noise blanker > works. Noise pulses are very narrow and very fast. If you look at them in > the frequency domain you will see that their spectrum is very broad. That > fast rise and fall time requires wide bandwidth to detect. After you detect > the pulse, you then blank the IF for the duration of the pulse. Basically > the receiver is "switched off" for the duration of the noise pulse. > > The problem with strong signals is that they are falsely detected as noise > pulses and cause the IF to be blanked. This is a form of amplitude > modulation that creates sidebands around every signal. Not good. But it is > potentially possible to make a NB that will be able to recognize the > difference between a very strong narrowband signal outside the passband and > a broadband noise pulse and NOT blank the receiver for strong narrowband > signals. But, right now, that software doesn't exist in PowerSDR. The good > thing is that there has been talk of writing such a noise blanker and > including it in PSDR. > > -- > Brian Lloyd, WB6RQN/J79BPL > 3191 Western Dr. > Cameron Park, CA 95682 > [email protected] > +1.767.617.1365 (Dominica) > +1.931.492.6776 (USA) > (+1.931.4.WB6RQN) > _______________________________________________ > Flexedge mailing list > [email protected] > http://mail.flex-radio.biz/mailman/listinfo/flexedge_flex-radio.biz > This is the FlexRadio Systems e-mail Reflector called FlexEdge. It is used > for posting topics related to SDR software development and experimentalist > who are using beta versions of the software. > _______________________________________________ Flexedge mailing list [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexedge_flex-radio.biz This is the FlexRadio Systems e-mail Reflector called FlexEdge. It is used for posting topics related to SDR software development and experimentalist who are using beta versions of the software. _______________________________________________ Flexedge mailing list [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexedge_flex-radio.biz This is the FlexRadio Systems e-mail Reflector called FlexEdge. It is used for posting topics related to SDR software development and experimentalist who are using beta versions of the software.
