I listen to the am talk radio during my commute. There are a couple places where the 60 and 120 hz hum from power lines drowns out the talk. Would a box with a 8.3ms delay filter this out some? (never mind the logistics of how to hook it into the darn radio...)
am radio buzz filter?
Started by ●May 16, 2006
Reply by ●May 16, 20062006-05-16
BobG wrote:> I listen to the am talk radio during my commute. There are a couple > places where the 60 and 120 hz hum from power lines drowns out the > talk. Would a box with a 8.3ms delay filter this out some? (never mind > the logistics of how to hook it into the darn radio...)Report the problem to the local power company (cc FCC). It's a sign of leakage, probably a bit of arcing, and an indication of energy loss. A filter at 60 Hz and its low harmonica might help, but a simple delay won't be effective. A pure delay will change nothing, and combining the signal with the original is just a way to make an overall comb filter. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●May 16, 20062006-05-16
Reply by ●May 16, 20062006-05-16
Jerry Avins wrote:> BobG wrote: > > > I listen to the am talk radio during my commute. There are a couple > > places where the 60 and 120 hz hum from power lines drowns out the > > talk. Would a box with a 8.3ms delay filter this out some? (never mind > > the logistics of how to hook it into the darn radio...) > > Report the problem to the local power company (cc FCC). It's a sign of > leakage, probably a bit of arcing, and an indication of energy loss. A > filter at 60 Hz and its low harmonica might help, but a simple delay > won't be effective. A pure delay will change nothing, and combining the > signal with the original is just a way to make an overall comb filter. > > Jerry > -- > Engineering is the art of making what you want from things you can get. > =AFThose 120 Hz discharges are extremely broadband. They appear impulsive in the time domain, the type of thing that a median filter can help with. I have also heard of this happening with light dimmers and other kinds of dirty equipment. John
Reply by ●May 16, 20062006-05-16
I thought the one cycle delay comb filter would catch all the harmonics at 120, 180, 240, 300 etc? Might sound like Icheekoo Park phasing though?
Reply by ●May 16, 20062006-05-16
naebad wrote:> An analogue notch filter will suffice.Notch at what frequency? Typically, there's significant energy at 900 Hz. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●May 16, 20062006-05-16
BobG wrote:> I listen to the am talk radio during my commute. There are a couple > places where the 60 and 120 hz hum from power lines drowns out the > talk. Would a box with a 8.3ms delay filter this out some? (never mind > the logistics of how to hook it into the darn radio...)a very interesting question... this is most effectively attacked at RF and is known as a noise blanker, As someone else said, these are repetitive very short very strong impulses. But once they hit the IF filter of the radio they create pulses that are wellll..... the impulse response of the IF filter which is typically very much longer in duration compared to the original impulse. So the bet way to attack it is to put a high speed broadband gate AHEAD of the narrow band IF filter. You need some kind of aux receiver tuned to a nearby but unused frequency and threshold to key this gate to block the impulse from hitting the IF. Since you are before the IF filter, the gate time can be made very short and if it all woks out right it can be very effective. This would be a great application for DSP but it would have to be done within the radio in the IF section... by the time you hit the detector it is too late... Second best is a simple audio limiter. The AM modulation depth of the station is limited to about 100% but the impulse can have an unlimited upwards modulation so the audio is very asymmetrical and a clipper can help but it is not nearly as effective as a true noise blanker... Mark
Reply by ●May 17, 20062006-05-17
"Jerry Avins" <jya@ieee.org> wrote in message news:vrudnWHnnssh0vfZRVn-gg@rcn.net...> naebad wrote: > > > An analogue notch filter will suffice. > > Notch at what frequency? Typically, there's significant energy at 900 Hz. > > Jerry > -- > Engineering is the art of making what you want from things you can get. > �����������������������������������������������������������������������Try the simple things first - 60Hz notch. M.P *** Posted via a free Usenet account from http://www.teranews.com ***
Reply by ●May 17, 20062006-05-17
"Mark" <makolber@yahoo.com> wrote in message news:1147833202.366083.124940@j33g2000cwa.googlegroups.com...> > BobG wrote: > > I listen to the am talk radio during my commute. There are a couple > > places where the 60 and 120 hz hum from power lines drowns out the > > talk. Would a box with a 8.3ms delay filter this out some? (never mind > > the logistics of how to hook it into the darn radio...) > > a very interesting question... > > this is most effectively attacked at RF and is known as a noise > blanker, > > As someone else said, these are repetitive very short very strong > impulses. But once they hit the IF filter of the radio they create > pulses that are wellll..... the impulse response of the IF filter which > is typically very much longer in duration compared to the original > impulse. So the bet way to attack it is to put a high speed > broadband gate AHEAD of the narrow band IF filter. You need some kind > of aux receiver tuned to a nearby but unused frequency and threshold to > key this gate to block the impulse from hitting the IF. Since you are > before the IF filter, the gate time can be made very short and if it > all woks out right it can be very effective. > > This would be a great application for DSP but it would have to be done > within the radio in the IF section... by the time you hit the detector > it is too late... > > Second best is a simple audio limiter. The AM modulation depth of the > station is limited to about 100% but the impulse can have an unlimited > upwards modulation so the audio is very asymmetrical and a clipper can > help but it is not nearly as effective as a true noise blanker... > > Mark >Limiters only amplify noise at low SNRs. They have no filtering effect at all. M.P *** Posted via a free Usenet account from http://www.teranews.com ***
Reply by ●May 17, 20062006-05-17
> > > Limiters only amplify noise at low SNRs. They have no filtering effect at > all. > >You are thinking of limiters like a DBX166 which are compressors and often called limiters by audio guys........I'm talking about instantaneous limiting or clipping,,, it's a terminology issue.. A clipper will slice off the peaks.... Mark
