RF Noise canceller ?
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Just a question for the technically inclined group members:
How feasible or worth the effort, would be the addition of an option to the K2 which would sample RF noise from a ferquency close to the used band,(tunable?) which is devoid of signals, phase invert and reinject the noise to an IF stage or even the antenna input in order to cancel our the "white or pulse" noise components, preserving the desired signal ? Why similar circuits are not preferred in HF receiver designs instead of DSP filters ? Similar circuits are commonly used in biomedical devices (called linear averagers if I am not mistaken) and are very effective in isolating electric signals from a particular organ eg Heart in EKG or brain area of interest in EEG, filtering out the irrelevant noise from the muscle cells... Just some food for thought. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Hello Marinos,
There have been several schematics using such technics over the last 20 years. Most of them use a seperate short antenna, feeding the signal pase shifted into a combiner which combines the main Antenna Signal with the phases shifted extra antenna signal. This construction can reduce a lot of man made noise. I remember there was a commercial available stand alone unit sold by a small english company. I myself built such a unit to help reducing my noise problem especialy at 160m (I live in the middle of Berlin, Noise level in the evening is > S7) But I forgot the unit during the time because I do not have an 160m Antenna any longer. 73 de Peter, DL2FI > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]] On Behalf Of > Marinos Markomanolakis, M.D. > Sent: Sunday, April 03, 2005 6:45 AM > To: [hidden email] > Subject: [Elecraft] RF Noise canceller ? > > Just a question for the technically inclined group members: > > How feasible or worth the effort, would be the addition of an > option to the > K2 which would sample RF noise from a ferquency close to the used > band,(tunable?) which is devoid of signals, phase invert and > reinject the noise to an IF stage or even the antenna input > in order to cancel our the "white or pulse" noise components, > preserving the desired signal ? > > Why similar circuits are not preferred in HF receiver designs > instead of DSP filters ? > > Similar circuits are commonly used in biomedical devices > (called linear averagers if I am not mistaken) and are very > effective in isolating electric signals from a particular > organ eg Heart in EKG or brain area of interest in EEG, > filtering out the irrelevant noise from the muscle cells... > > Just some food for thought. > > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Marinos
http://www.mfjenterprises.com/products.php?prodid=MFJ-1025
http://www.w8ji.com/mfj-1025_1026.htm 73, Bill W4ZV _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Peter Zenker
Hi Peter,
Would this type of noise canceler not work on "white" noise also ? 73, Marinos, ki4gin >From: "Peter Zenker" <[hidden email]> >To: "'Marinos Markomanolakis, M.D.'" ><[hidden email]>,<[hidden email]> >Subject: RE: [Elecraft] RF Noise canceller ? >Date: Sun, 3 Apr 2005 13:03:51 +0200 > >Hello Marinos, > >There have been several schematics using such technics over the last 20 >years. Most of them use a seperate short antenna, feeding the signal pase >shifted into a combiner which combines the main Antenna Signal with the >phases shifted extra antenna signal. This construction can reduce a lot of >man made noise. >I remember there was a commercial available stand alone unit sold by a >small >english company. >I myself built such a unit to help reducing my noise problem especialy at >160m (I live in the middle of Berlin, Noise level in the evening is > S7) >But I forgot the unit during the time because I do not have an 160m Antenna >any longer. > >73 de Peter, DL2FI > > > -----Original Message----- > > From: [hidden email] > > [mailto:[hidden email]] On Behalf Of > > Marinos Markomanolakis, M.D. > > Sent: Sunday, April 03, 2005 6:45 AM > > To: [hidden email] > > Subject: [Elecraft] RF Noise canceller ? > > > > Just a question for the technically inclined group members: > > > > How feasible or worth the effort, would be the addition of an > > option to the > > K2 which would sample RF noise from a ferquency close to the used > > band,(tunable?) which is devoid of signals, phase invert and > > reinject the noise to an IF stage or even the antenna input > > in order to cancel our the "white or pulse" noise components, > > preserving the desired signal ? > > > > Why similar circuits are not preferred in HF receiver designs > > instead of DSP filters ? > > > > Similar circuits are commonly used in biomedical devices > > (called linear averagers if I am not mistaken) and are very > > effective in isolating electric signals from a particular > > organ eg Heart in EKG or brain area of interest in EEG, > > filtering out the irrelevant noise from the muscle cells... > > > > Just some food for thought. > > > > > > _______________________________________________ > > Elecraft mailing list > > Post to: [hidden email] > > You must be a subscriber to post to the list. > > Subscriber Info (Addr. Change, sub, unsub etc.): > > http://mailman.qth.net/mailman/listinfo/elecraft > > > > Help: http://mailman.qth.net/subscribers.htm > > Elecraft web page: http://www.elecraft.com > > > > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Marinos
In a message dated 03/04/05 12:11:33 GMT Daylight Time, [hidden email] writes: There have been several schematics using such technics over the last 20 years. Most of them use a seperate short antenna, feeding the signal pase shifted into a combiner which combines the main Antenna Signal with the phases shifted extra antenna signal. This construction can reduce a lot of man made noise. I remember there was a commercial available stand alone unit sold by a small english company. ------------------------------------------- The Antenna interference cancelling unit in the UK was from SEM a company in the Isle of Man (GD). No longer seem to be in business. There is one from MFJ still on the market and believe a model may have come from a company called NIR (now part of Timewave? cannot find any info on the Timewave web site) though could be wrong on this latter unit. I built my own from a design from G4WMX for a "Null Steerer" that was circulating in the UK in 1989. I can remember my late father in law Ted, G3UUA building one at the time and was impressed with how well it worked, taking his S9 level of interference out totally. About two years back when suffering from local electrical interference I had a go at building the same unit. There is a PCB produced by Geoff Steedman, M0BGS available now as well as a kit of parts to populate the bare PCB. For the kit of parts with PCB, I paid £25 (US$47 approx). Built it up into a diecast box and have it permanently in the RX antenna feed. Easy for me as I have a separate TX/RX on the QRO rig. Alternately has PTT switch feed to enable it to be used in the antenna feed of a 100W HF transceiver. With a suitable auxiliary antenna it can null out quite high levels of local interference, the limiting factor being the amount of wanted signal also picked up by the auxiliary antenna. With the power off the unit is totally bypassed. The downside with mine is that with the unit active, the wanted signal is attenuated somewhat and even more when nulling out interference. The upside is that it can still make a vital difference in hearing signals buried under local interference. I believe Geoff, M0BGS has modified more recent PCB to add an emitter follower to the outgoing main antenna feed to offset through losses. Will have to try to modify my PCB to add this. I have the scanned circuit and notes somewhere in my PC for the original unit before the emitter follower was added. If anybody wants to have a go at constructing this device and needs the info, contact me direct. Bob, G3VVT _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Marinos
I think no.
White noise by definition is no statistic, therefore IMO it cannot be eliminated because at no time it has a defined phase angle. 73 de Peter > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]] On Behalf Of > Marinos Markomanolakis, M.D. > Sent: Sunday, April 03, 2005 3:26 PM > To: [hidden email] > Cc: [hidden email] > Subject: RE: [Elecraft] RF Noise canceller ? > > Hi Peter, > Would this type of noise canceler not work on "white" noise also ? > 73, > Marinos, ki4gin > > >From: "Peter Zenker" <[hidden email]> > >To: "'Marinos Markomanolakis, M.D.'" > ><[hidden email]>,<[hidden email]> > >Subject: RE: [Elecraft] RF Noise canceller ? > >Date: Sun, 3 Apr 2005 13:03:51 +0200 > > > >Hello Marinos, > > > >There have been several schematics using such technics over > the last 20 > >years. Most of them use a seperate short antenna, feeding the signal > >pase shifted into a combiner which combines the main Antenna Signal > >with the phases shifted extra antenna signal. This construction can > >reduce a lot of man made noise. > >I remember there was a commercial available stand alone unit > sold by a > >small english company. > >I myself built such a unit to help reducing my noise problem > especialy > >at 160m (I live in the middle of Berlin, Noise level in the > evening is > >> S7) But I forgot the unit during the time because I do not have an > >160m Antenna any longer. > > > >73 de Peter, DL2FI > > > > > -----Original Message----- > > > From: [hidden email] > > > [mailto:[hidden email]] On Behalf Of Marinos > > > Markomanolakis, M.D. > > > Sent: Sunday, April 03, 2005 6:45 AM > > > To: [hidden email] > > > Subject: [Elecraft] RF Noise canceller ? > > > > > > Just a question for the technically inclined group members: > > > > > > How feasible or worth the effort, would be the addition > of an option > > > to the > > > K2 which would sample RF noise from a ferquency close to the used > > > band,(tunable?) which is devoid of signals, phase invert and > > > reinject the noise to an IF stage or even the antenna > input in order > > > to cancel our the "white or pulse" noise components, > preserving the > > > desired signal ? > > > > > > Why similar circuits are not preferred in HF receiver designs > > > instead of DSP filters ? > > > > > > Similar circuits are commonly used in biomedical devices (called > > > linear averagers if I am not mistaken) and are very effective in > > > isolating electric signals from a particular organ eg > Heart in EKG > > > or brain area of interest in EEG, filtering out the > irrelevant noise > > > from the muscle cells... > > > > > > Just some food for thought. > > > > > > > > > _______________________________________________ > > > Elecraft mailing list > > > Post to: [hidden email] > > > You must be a subscriber to post to the list. > > > Subscriber Info (Addr. Change, sub, unsub etc.): > > > http://mailman.qth.net/mailman/listinfo/elecraft > > > > > > Help: http://mailman.qth.net/subscribers.htm > > > Elecraft web page: http://www.elecraft.com > > > > > > > > > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Marinos
-----Original Message----- Would this type of noise canceler not work on "white" noise also ? _______________________________ The simplest answer is no. White noise typically arrives from random directions, with random phases, random polarizations, etc. etc. etc. and are usually from thermal and uncorrelated sources. The principle of operation of these phasing units IS THAT THEY CAN BE PHASED to eliminate unwanted signals since they are from a sufficiently point like source that a null can be tuned on top of them. How is this done? You can arrange to add an interfering signal 180 degrees out of phase with one from the intended antenna while not killing the signal of interest to the point it is not heard. In other words, you increase the signal to (signal+interference) ratio. To the extent that this is automated, it is a "smart antenna". The importance of them having equal responses to the interferer so that simple phasing works is a tricky business. If amplification is required to do this, then you have the myriad problems (IP3, IMD, DR, MDS, etc) to deal with in this new system. Since we are not asking for a perfect null, but some serious suppression, these conditions can be relaxed. If the noise source is localized or coming from a direction that is not nearly collinear (within the 3dB beamwidth of say a directive antenna) with the signal of interest, it can be nulled with these phasing methods irrespective of its power spectral distribution, white, poisson, tone, etc. This is all reasonably complicated as you can see. Bob N4HY _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Peter Zenker
> Would this type of noise canceler not work on "white" noise also ? 73,
> Marinos, ki4gin > That depends a lot on the source of the noise, broadband (white) or otherwise. These circuits depend upon a second antenna picking up the noise better than the signal. Then the signal from the "noise" antenna is inverted and added to the signal from the main antenna. Adjustment of both phase and the signal levels in the circuit is required so that when a pulse of noise from one antenna hits, say +10 uV, the same pulse from the other antenna hits - 10 uV at the same instant so they add together and produce an output of zero volts. The result is that the noise is cancelled out while, hopefully, the signal remains. Even a wire on the ground will pick up a distant signal. Indeed, a wire on the ground sometimes picks up the signal with less noise that a huge wire in the air! One of the most effective "low noise" receiving antennas known is a wire on the ground or sometimes even buried a few inches below the surface of the earth! (And insulated). So the noise canceling system works in some situations and not in others. As one person pointed out, it often results in significant attenuation of the desired signal too when the desired signal is being picked up by both antennas. How well the system works on broadband noise depends upon how stable the phase relationship remains between them. Some noise will arrive via ground wave, multiple reflections from the ionosphere and even reflections from nearby objects that may shift constantly. That will cause the phase relationship, and the degree of cancellation, to shift considerably as well. For that reason these blankers have been most effective on locally-generated noise arriving by stable ground wave. Sky wave noise simply shifts too much to provide a useful null. I have what many Hams call (for the lack of a better word) a "counterpoise" that I often use with tinkering with end-fed radiators. It's simply a wire about a meter or so off of the ground that runs from the shack window in two directions: along a porch in one direction and along a fence in another direction. I have found that this low, random wire sometimes makes a superb receiving antenna. Often I can hear signals better using it than using my doublet overhead, especially on the lower bands, thanks to a much lower noise level it picks up. That fits with regular reports over the decades that noise is often attenuated far more by the earth than the signals arriving via sky wave. Sure, signals overall are weaker with an antenna near the ground, but that is of absolutely no consequence. In receive, antenna gain is unimportant as long as the receiver signal-to-noise ratio is such that the internally-generated receiver noise won't mask the signals. Any of the HF Elecraft rigs has an internal noise level that will allow even a very lossy, small antenna to be used to maximum effectiveness when receiving. Just turn on the preamplifier or turn up the volume to make up for the low signals from the antenna. Using my "counterpoise" for a receiving antenna often gives me huge improvement in signal to noise levels, especially on 160 and 80 meters. Some Hams have reported excellent results receiving on a length of old coax thrown on the ground! Bottom line: The noise canceling system seems to be most effective when the noise antenna can be positioned so as to pick up the noise much better than it can the signal, and the noise source is nearby and providing a stable phase relationship at both antennas. A purpose-built receiving antenna close to the ground may be more effective, especially when trying to pull weak DX out of the noise level. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Robert McGwier
-----Original Message-----
Would this type of noise canceler not work on "white" noise also ? ______________________________ White noise typically arrives from random directions, with random phases, random polarizations, etc. etc. etc. and are usually from thermal and uncorrelated sources. ------- <pick on details> If you want to use the proper signal processing terminology here, then white noise is a spectral property and only means broadband. It says nothing about directionality. The corresponding directional term is isotropic noise. So the answer is that the noise canceller works for noise sources with directionality, white or not does not matter as our radios are narrowband anyway. The assumption is that the noise is directional so that two antennas can receive different proportions of signal and noise. The canceller will not work with isotropic noise sources. </detail picking> 73 Sverre LA3ZA http://www.qsl.net/la3za/ _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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