Forums

Automatic RF noise cancellation and audio noise measurement

Started by Jason Hsu August 5, 2003
THE BIG QUESTION: How do you measure the audio noise level in a
receiver?  Does anyone here know of any circuits that show the overall
audio noise level?

Let me tell you what this is all about.

SIDE NOTE: Thanks again to those of you who helped me with the
SWR/wattmeter project I worked on last semester.  This project taught
me more about ferrite cores, op amps, and diodes than ANY class
possibly could.  I learned about stray capacitance and what rails
mean.  I also learned that not all 1N34A diodes are alike.

In this coming semester, I will be working on an even more ambitious
project - an automatic noise canceller for 160m to 10m.  It will
definitely be a control system, and it may even use DSP.  The device
will also require a motor for automatically adjusting the controls. 
The idea is to design and build an automatic version of the Timewave
ANC-4 or the MFJ-1025/1026 RF noise cancellers.

The ANC-4 and MFJ-1025/1026 are manual devices.  There are automatic
noise cancellation devices, but their adjustments are at the audio
level rather than the RF level.

The back panel of my device will contain:
1.  Connector for the signal antenna
2.  Connector for the transceiver
3.  Connector for the noise antenna
4.  DC power connector

The front panel of my device will contain:
1.  Power switch and the obligatory idiot light to show that the power
is on
2.  2 audio connectors: one connects to the transceiver, and the other
connects to an external speaker
3.  Frequency range control for choosing the inductance values, as the
proper inductance values in the RF noise cancelling circuit varies
with frequency
4.  Phase range knob so that the phase shifter can cover all 360
degrees
5.  Manual noise phase knob
6.  Manual noise gain knob
7.  LED display to show the noise level
8.  Noise phase adjustment push-button: Pressing this button activates
the control system to adjust the phase shift of the noise.
9.  Noise gain adjustment button: Pressing this button activates the
control system to adjust the gain of the noise.

Other features:
1.  I need to design my automatic noise canceller so that parts won't
blow up if I transmit 100W through it.  This probably requires some
type of automatic bypass circuitry.
2.  Transmitted power must not reach the noise antenna (at least not
without a great deal of attenuation)
3.  It also needs a low insertion loss.
4.  A preamplifier would be desirable.

How it would work:
1.  You manually turn the phase and gain controls to the minimum
settings.  (Or I could put in a reset button to do that.  No, that
would add too much complexity to the circuit.)
2.  You select the band using the band inductance switch.
3.  You move the phase polarity switch to the negative setting.  If
the  noise cancellation procedure does not work, it probably means the
opposite setting is required.
4.  Press the noise gain adjustment button.  The device adjusts the
noise gain until a change in the signal level (or the S meter) is just
noted.  (Some type of derivative function would come into play.)
5.  Press the noise phase adjustment button.  The device adjusts the
noise phase shift so as to produce a null in the signal level (or the
S meter).
6.  Steps 4 and 5 could be repeated to make further adjustments. 
There might be away to activate the control system with just one
button.

Does anyone know of circuits that measure audio noise?  Making the RF
noise canceller automatic requires an audio circuit to monitor the
noise level.  This noise level needs to be converted into a large DC
voltage, which feeds the motors that turn the variable capacitor and
potentiometer.

Jason Hsu, AG4DG
usenet@@@@jasonhsu.com
"Jason Hsu" <jason_hsu@my-deja.com> wrote in message
news:f7d9a152.0308051412.54d4c913@posting.google.com...
> THE BIG QUESTION: How do you measure the audio noise level in a > receiver? Does anyone here know of any circuits that show the overall > audio noise level? > > Let me tell you what this is all about. > > SIDE NOTE: Thanks again to those of you who helped me with the > SWR/wattmeter project I worked on last semester. This project taught > me more about ferrite cores, op amps, and diodes than ANY class > possibly could. I learned about stray capacitance and what rails > mean. I also learned that not all 1N34A diodes are alike. > > In this coming semester, I will be working on an even more ambitious > project - an automatic noise canceller for 160m to 10m. It will > definitely be a control system, and it may even use DSP. The device > will also require a motor for automatically adjusting the controls. > The idea is to design and build an automatic version of the Timewave > ANC-4 or the MFJ-1025/1026 RF noise cancellers. > > The ANC-4 and MFJ-1025/1026 are manual devices. There are automatic > noise cancellation devices, but their adjustments are at the audio > level rather than the RF level. > > The back panel of my device will contain: > 1. Connector for the signal antenna > 2. Connector for the transceiver > 3. Connector for the noise antenna > 4. DC power connector > > The front panel of my device will contain: > 1. Power switch and the obligatory idiot light to show that the power > is on > 2. 2 audio connectors: one connects to the transceiver, and the other > connects to an external speaker > 3. Frequency range control for choosing the inductance values, as the > proper inductance values in the RF noise cancelling circuit varies > with frequency > 4. Phase range knob so that the phase shifter can cover all 360 > degrees > 5. Manual noise phase knob > 6. Manual noise gain knob > 7. LED display to show the noise level > 8. Noise phase adjustment push-button: Pressing this button activates > the control system to adjust the phase shift of the noise. > 9. Noise gain adjustment button: Pressing this button activates the > control system to adjust the gain of the noise. > > Other features: > 1. I need to design my automatic noise canceller so that parts won't > blow up if I transmit 100W through it. This probably requires some > type of automatic bypass circuitry. > 2. Transmitted power must not reach the noise antenna (at least not > without a great deal of attenuation) > 3. It also needs a low insertion loss. > 4. A preamplifier would be desirable. > > How it would work: > 1. You manually turn the phase and gain controls to the minimum > settings. (Or I could put in a reset button to do that. No, that > would add too much complexity to the circuit.) > 2. You select the band using the band inductance switch. > 3. You move the phase polarity switch to the negative setting. If > the noise cancellation procedure does not work, it probably means the > opposite setting is required. > 4. Press the noise gain adjustment button. The device adjusts the > noise gain until a change in the signal level (or the S meter) is just > noted. (Some type of derivative function would come into play.) > 5. Press the noise phase adjustment button. The device adjusts the > noise phase shift so as to produce a null in the signal level (or the > S meter). > 6. Steps 4 and 5 could be repeated to make further adjustments. > There might be away to activate the control system with just one > button. > > Does anyone know of circuits that measure audio noise? Making the RF > noise canceller automatic requires an audio circuit to monitor the > noise level. This noise level needs to be converted into a large DC > voltage, which feeds the motors that turn the variable capacitor and > potentiometer. > > Jason Hsu, AG4DG > usenet@@@@jasonhsu.com
Allow me to infuse a different idea. Think about noise as a fairly broadband phenomenon. The same atmospheric noise that you hear on 21.500 Mhz will also be heard on 21.510 Mhz. Consider the possibility of biulding two identical receivers, the main receiver tuned to the desired reception frequency, the other tuned just a few Khz away, but out of the received signal's bandwidth. Then, you detect the noise on the second receiver, invert it, and sum it into the first receiver's signal chain. This concept is used in ultra-low noise, high sensitivity deep space receivers to almost totally eliminate noise in the received signal. Now, as to your concern to keep 100W of RF from blowing up your noise canceller. That's what antenna changeover relays are for. They normally connect the antenna to the receiver, but when the transmitter is keyed up, the relay connects the antenna to the transmitter output, and disconnects it from the receiver. Simple, but effective, and has been used for many many years in amateur as well as commercial radio equipment. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Time is what keeps everything from happening all at once.
There are numerous sources of noise at the input to a receiver:

1) Background HF noise that exhibits a 1/f rolloff characteristic. This 
has seasonal and diurnal variations.

2) Atmospheric noise caused by local or near local weather. Remember 
there are 10,000 thunderstorms in the world at any time.

3) Solar flare noise. During an solar X-ray event the HF noise, #1, can 
increase by over 60 dB for short periods of time.

4) Local line interference noise.

5) In the future, BPL noise.

6) I'm sure there are other noise sources such as defective insulators 
on power lines.   ;-)

The ANC-4 and MFJ 1025/1026 ONLY operate on #4.

So, your first task is to become familiar with the spectral 
characteristics of each so you can design a basic filtering circuit for 
the undesired noise source. My ANC-4 does not respond to the 1/f HF 
solar noise sources, atmospheric induced noise or solar flare noise.

Weather induced noise contains frequency components that are in the 
audio passband, you can hear lightning induced static crashes in your 
SSB/AM radio. How will you discriminate between desired audio and static 
audio?

Solar flare noise sounds like a slowly rising rushing hiss in the 
receiver. It has a slow rise time generally in the range of tens of 
seconds to minutes. It is broadbanded and will easily over ride any low 
level desired signal. The noise to signal, NOT signal to noise,  ratio 
can easily exceed 40 dB making detection almost impossible. These 
characteristics are proportional to the intensity of the solar flux and 
also the wavelength of the solar flux. Detecting desired signals in this 
environment is extraordinarily difficult.

Manmade noise, these are processed by the ANC-4 and MFJ units, contains 
basically repetitive waveforms from TVs, VCRs, Remotes, Routers, 
Computers, etc.

A design approach would be to use digital filtering and a series of 
Kalman filters [digital filter algorithms], assuming they are available 
to the general public. The Kalman filters would be tailored to the 
spectral content of the noise source you are attempting to cancel. A 
second design approach would be a fast Fourier transform that 
discriminates N/S from S/N. You want to keep the noise OUT of the FIRST 
RF STAGE to avoid pumping the AGC and getting false signals. For HF 
digital filtering this will require a very fast processor [possibly GHz 
range]

How to measure the AF noise from a receiver? I'd start by looking into a 
Bolometer circuit with AC coupling. This would give a pseudo RMS reading 
that could be used as a reference for a series of servo based op-amps to 
control your gain and phase circuits.

Depending on how far you want to pursue the science it could be a very 
interesting project.

With a statement of principles it is YOUR Project, NOT the project for 
the members of this list. So, go and have fun!

Deacon Dave, W1MCE

Among the many components of my background was 7 years as Project 
Engineer designing special test equipment on contract for the USAF.

Jason:

Very similar to what you are describing is popularly known as a "Noise
Blanker"  Motorola introduced their design for mobile radios in 1959 as an
"Extender"  In the same time frame, Collins offered a model for the S-Line
and KWM-2.  I designed a tube model for GE's Progress Line radios, and I
forget who designed the solid state version.  The concept has been described
in numerous places, so do a bibliographic search of Engineering Index, or
Scientific Abstracts, or whatever that school has access to.  You also need
to familiarize yourself with the concepts involved in noise balanced
squelch, which was patented by Motorola back in the late 30s or early 40s.
It will tell you how to do the audio noise level measurement meaningfully
and apply it usefully.

--
Crazy George
Remove NO and SPAM from return address
"Jason Hsu" <jason_hsu@my-deja.com> wrote in message
news:f7d9a152.0308051412.54d4c913@posting.google.com...
> THE BIG QUESTION: How do you measure the audio noise level in a > receiver? Does anyone here know of any circuits that show the overall > audio noise level? > > Let me tell you what this is all about. > > SIDE NOTE: Thanks again to those of you who helped me with the > SWR/wattmeter project I worked on last semester. This project taught > me more about ferrite cores, op amps, and diodes than ANY class > possibly could. I learned about stray capacitance and what rails > mean. I also learned that not all 1N34A diodes are alike. > > In this coming semester, I will be working on an even more ambitious > project - an automatic noise canceller for 160m to 10m. It will > definitely be a control system, and it may even use DSP. The device > will also require a motor for automatically adjusting the controls. > The idea is to design and build an automatic version of the Timewave > ANC-4 or the MFJ-1025/1026 RF noise cancellers. > > The ANC-4 and MFJ-1025/1026 are manual devices. There are automatic > noise cancellation devices, but their adjustments are at the audio > level rather than the RF level. > > The back panel of my device will contain: > 1. Connector for the signal antenna > 2. Connector for the transceiver > 3. Connector for the noise antenna > 4. DC power connector > > The front panel of my device will contain: > 1. Power switch and the obligatory idiot light to show that the power > is on > 2. 2 audio connectors: one connects to the transceiver, and the other > connects to an external speaker > 3. Frequency range control for choosing the inductance values, as the > proper inductance values in the RF noise cancelling circuit varies > with frequency > 4. Phase range knob so that the phase shifter can cover all 360 > degrees > 5. Manual noise phase knob > 6. Manual noise gain knob > 7. LED display to show the noise level > 8. Noise phase adjustment push-button: Pressing this button activates > the control system to adjust the phase shift of the noise. > 9. Noise gain adjustment button: Pressing this button activates the > control system to adjust the gain of the noise. > > Other features: > 1. I need to design my automatic noise canceller so that parts won't > blow up if I transmit 100W through it. This probably requires some > type of automatic bypass circuitry. > 2. Transmitted power must not reach the noise antenna (at least not > without a great deal of attenuation) > 3. It also needs a low insertion loss. > 4. A preamplifier would be desirable. > > How it would work: > 1. You manually turn the phase and gain controls to the minimum > settings. (Or I could put in a reset button to do that. No, that > would add too much complexity to the circuit.) > 2. You select the band using the band inductance switch. > 3. You move the phase polarity switch to the negative setting. If > the noise cancellation procedure does not work, it probably means the > opposite setting is required. > 4. Press the noise gain adjustment button. The device adjusts the > noise gain until a change in the signal level (or the S meter) is just > noted. (Some type of derivative function would come into play.) > 5. Press the noise phase adjustment button. The device adjusts the > noise phase shift so as to produce a null in the signal level (or the > S meter). > 6. Steps 4 and 5 could be repeated to make further adjustments. > There might be away to activate the control system with just one > button. > > Does anyone know of circuits that measure audio noise? Making the RF > noise canceller automatic requires an audio circuit to monitor the > noise level. This noise level needs to be converted into a large DC > voltage, which feeds the motors that turn the variable capacitor and > potentiometer. > > Jason Hsu, AG4DG > usenet@@@@jasonhsu.com
Whit all that said, I can design a Mouse that looks like an Elephant <grin>

Deacon Dave, W1MCE

Dave Shrader wrote:

> There are numerous sources of noise at the input to a receiver: > > 1) Background HF noise that exhibits a 1/f rolloff characteristic. This > has seasonal and diurnal variations. > > 2) Atmospheric noise caused by local or near local weather. Remember > there are 10,000 thunderstorms in the world at any time. > > 3) Solar flare noise. During an solar X-ray event the HF noise, #1, can > increase by over 60 dB for short periods of time. > > 4) Local line interference noise. > > 5) In the future, BPL noise. > > 6) I'm sure there are other noise sources such as defective insulators > on power lines. ;-) > > The ANC-4 and MFJ 1025/1026 ONLY operate on #4. > > So, your first task is to become familiar with the spectral > characteristics of each so you can design a basic filtering circuit for > the undesired noise source. My ANC-4 does not respond to the 1/f HF > solar noise sources, atmospheric induced noise or solar flare noise. > > Weather induced noise contains frequency components that are in the > audio passband, you can hear lightning induced static crashes in your > SSB/AM radio. How will you discriminate between desired audio and static > audio? > > Solar flare noise sounds like a slowly rising rushing hiss in the > receiver. It has a slow rise time generally in the range of tens of > seconds to minutes. It is broadbanded and will easily over ride any low > level desired signal. The noise to signal, NOT signal to noise, ratio > can easily exceed 40 dB making detection almost impossible. These > characteristics are proportional to the intensity of the solar flux and > also the wavelength of the solar flux. Detecting desired signals in this > environment is extraordinarily difficult. > > Manmade noise, these are processed by the ANC-4 and MFJ units, contains > basically repetitive waveforms from TVs, VCRs, Remotes, Routers, > Computers, etc. > > A design approach would be to use digital filtering and a series of > Kalman filters [digital filter algorithms], assuming they are available > to the general public. The Kalman filters would be tailored to the > spectral content of the noise source you are attempting to cancel. A > second design approach would be a fast Fourier transform that > discriminates N/S from S/N. You want to keep the noise OUT of the FIRST > RF STAGE to avoid pumping the AGC and getting false signals. For HF > digital filtering this will require a very fast processor [possibly GHz > range] > > How to measure the AF noise from a receiver? I'd start by looking into a > Bolometer circuit with AC coupling. This would give a pseudo RMS reading > that could be used as a reference for a series of servo based op-amps to > control your gain and phase circuits. > > Depending on how far you want to pursue the science it could be a very > interesting project. > > With a statement of principles it is YOUR Project, NOT the project for > the members of this list. So, go and have fun! > > Deacon Dave, W1MCE > > Among the many components of my background was 7 years as Project > Engineer designing special test equipment on contract for the USAF. >
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Hi Jason:

I think the "signal antenna" and "noise antenna" are both just 
antennas.  I can't see how you can make an antenna that only hears noise 
and another that hears the same noise and signal.  If that's the case 
then by adjusting the relative phase and amplitude of the two "antennas" 
what you are doing is changing the antenna pattern.  This will improve 
the overall s/n if there is a source of noise that's coming form some 
direction more than from everywhere.

In "Beam and null switch step steerable antenna system" U.S. patent 
<http://www.delphion.com/> 4,063,250 
<http://www.delphion.com/details?&pn=US04063250__>  Fenwick has an 
antenna system where the main lobe is steered using time delay beam 
steering (this is a frequency independent version of a phased array) and 
in addition can steer a null independent of the main lobe.  He used 
mechanical relays and coax line, but a more modern version could use PIN 
diodes and a computer to try all the possible main and null lobe 
possibilities and use the best ones.

To measure the sensivity of an AM receiver you measure the RMS audio 
output voltage with a signal present and without a signal present.
For a more detailed look at the noise you need a spectrum analyzer, like 
the HP-Agilent 4395A that can make true RMS noise measurements, see:
http://www.pacificsites.com/~brooke/4395A.shtml

Have Fun,

Brooke Clarke, N6GCE
http://www.pacificsites.com/~brooke/electron.shtml#Antenna
Jason Hsu wrote:

>THE BIG QUESTION: How do you measure the audio noise level in a >receiver? Does anyone here know of any circuits that show the overall >audio noise level? > >Let me tell you what this is all about. > >SIDE NOTE: Thanks again to those of you who helped me with the >SWR/wattmeter project I worked on last semester. This project taught >me more about ferrite cores, op amps, and diodes than ANY class >possibly could. I learned about stray capacitance and what rails >mean. I also learned that not all 1N34A diodes are alike. > >In this coming semester, I will be working on an even more ambitious >project - an automatic noise canceller for 160m to 10m. It will >definitely be a control system, and it may even use DSP. The device >will also require a motor for automatically adjusting the controls. >The idea is to design and build an automatic version of the Timewave >ANC-4 or the MFJ-1025/1026 RF noise cancellers. > >The ANC-4 and MFJ-1025/1026 are manual devices. There are automatic >noise cancellation devices, but their adjustments are at the audio >level rather than the RF level. > >The back panel of my device will contain: >1. Connector for the signal antenna >2. Connector for the transceiver >3. Connector for the noise antenna >4. DC power connector > >The front panel of my device will contain: >1. Power switch and the obligatory idiot light to show that the power >is on >2. 2 audio connectors: one connects to the transceiver, and the other >connects to an external speaker >3. Frequency range control for choosing the inductance values, as the >proper inductance values in the RF noise cancelling circuit varies >with frequency >4. Phase range knob so that the phase shifter can cover all 360 >degrees >5. Manual noise phase knob >6. Manual noise gain knob >7. LED display to show the noise level >8. Noise phase adjustment push-button: Pressing this button activates >the control system to adjust the phase shift of the noise. >9. Noise gain adjustment button: Pressing this button activates the >control system to adjust the gain of the noise. > >Other features: >1. I need to design my automatic noise canceller so that parts won't >blow up if I transmit 100W through it. This probably requires some >type of automatic bypass circuitry. >2. Transmitted power must not reach the noise antenna (at least not >without a great deal of attenuation) >3. It also needs a low insertion loss. >4. A preamplifier would be desirable. > >How it would work: >1. You manually turn the phase and gain controls to the minimum >settings. (Or I could put in a reset button to do that. No, that >would add too much complexity to the circuit.) >2. You select the band using the band inductance switch. >3. You move the phase polarity switch to the negative setting. If >the noise cancellation procedure does not work, it probably means the >opposite setting is required. >4. Press the noise gain adjustment button. The device adjusts the >noise gain until a change in the signal level (or the S meter) is just >noted. (Some type of derivative function would come into play.) >5. Press the noise phase adjustment button. The device adjusts the >noise phase shift so as to produce a null in the signal level (or the >S meter). >6. Steps 4 and 5 could be repeated to make further adjustments. >There might be away to activate the control system with just one >button. > >Does anyone know of circuits that measure audio noise? Making the RF >noise canceller automatic requires an audio circuit to monitor the >noise level. This noise level needs to be converted into a large DC >voltage, which feeds the motors that turn the variable capacitor and >potentiometer. > >Jason Hsu, AG4DG >usenet@@@@jasonhsu.com > >
--------------000508040503080405070006 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta http-equiv="Content-Type" content="text/html;charset=ISO-8859-1"> <title></title> </head> <body text="#000000" bgcolor="#ffffff"> Hi Jason:<br> <br> I think the "signal antenna" and "noise antenna" are both just antennas.&nbsp; I can't see how you can make an antenna that only hears noise and another that hears the same noise and signal.&nbsp; If that's the case then by adjusting the relative phase and amplitude of the two "antennas" what you are doing is changing the antenna pattern.&nbsp; This will improve the overall s/n if there is a source of noise that's coming form some direction more than from everywhere.<br> <br> In "Beam and null switch step steerable antenna system" <a href="http://www.delphion.com/">U.S. patent</a><b><font color="#000000"> <a href="http://www.delphion.com/details?&amp;pn=US04063250__">4,063,250</a>&nbsp; </font></b>Fenwick has an antenna system where the main lobe is steered using time delay beam steering (this is a frequency independent version of a phased array) and in addition can steer a null independent of the main lobe.&nbsp; He used mechanical relays and coax line, but a more modern version could use PIN diodes and a computer to try all the possible main and null lobe possibilities and use the best ones.<br> <br> To measure the sensivity of an AM receiver you measure the RMS audio output voltage with a signal present and without a signal present.<br> For a more detailed look at the noise you need a spectrum analyzer, like the HP-Agilent 4395A that can make true RMS noise measurements, see:<br> <a class="moz-txt-link-freetext" href="http://www.pacificsites.com/~brooke/4395A.shtml">http://www.pacificsites.com/~brooke/4395A.shtml</a><br> <br> Have Fun,<br> <br> Brooke Clarke, N6GCE<br> <a class="moz-txt-link-freetext" href="http://www.pacificsites.com/~brooke/electron.shtml#Antenna">http://www.pacificsites.com/~brooke/electron.shtml#Antenna</a><br> Jason Hsu wrote:<br> <blockquote type="cite" cite="midf7d9a152.0308051412.54d4c913@posting.google.com"> <pre wrap="">THE BIG QUESTION: How do you measure the audio noise level in a receiver? Does anyone here know of any circuits that show the overall audio noise level? Let me tell you what this is all about. SIDE NOTE: Thanks again to those of you who helped me with the SWR/wattmeter project I worked on last semester. This project taught me more about ferrite cores, op amps, and diodes than ANY class possibly could. I learned about stray capacitance and what rails mean. I also learned that not all 1N34A diodes are alike. In this coming semester, I will be working on an even more ambitious project - an automatic noise canceller for 160m to 10m. It will definitely be a control system, and it may even use DSP. The device will also require a motor for automatically adjusting the controls. The idea is to design and build an automatic version of the Timewave ANC-4 or the MFJ-1025/1026 RF noise cancellers. The ANC-4 and MFJ-1025/1026 are manual devices. There are automatic noise cancellation devices, but their adjustments are at the audio level rather than the RF level. The back panel of my device will contain: 1. Connector for the signal antenna 2. Connector for the transceiver 3. Connector for the noise antenna 4. DC power connector The front panel of my device will contain: 1. Power switch and the obligatory idiot light to show that the power is on 2. 2 audio connectors: one connects to the transceiver, and the other connects to an external speaker 3. Frequency range control for choosing the inductance values, as the proper inductance values in the RF noise cancelling circuit varies with frequency 4. Phase range knob so that the phase shifter can cover all 360 degrees 5. Manual noise phase knob 6. Manual noise gain knob 7. LED display to show the noise level 8. Noise phase adjustment push-button: Pressing this button activates the control system to adjust the phase shift of the noise. 9. Noise gain adjustment button: Pressing this button activates the control system to adjust the gain of the noise. Other features: 1. I need to design my automatic noise canceller so that parts won't blow up if I transmit 100W through it. This probably requires some type of automatic bypass circuitry. 2. Transmitted power must not reach the noise antenna (at least not without a great deal of attenuation) 3. It also needs a low insertion loss. 4. A preamplifier would be desirable. How it would work: 1. You manually turn the phase and gain controls to the minimum settings. (Or I could put in a reset button to do that. No, that would add too much complexity to the circuit.) 2. You select the band using the band inductance switch. 3. You move the phase polarity switch to the negative setting. If the noise cancellation procedure does not work, it probably means the opposite setting is required. 4. Press the noise gain adjustment button. The device adjusts the noise gain until a change in the signal level (or the S meter) is just noted. (Some type of derivative function would come into play.) 5. Press the noise phase adjustment button. The device adjusts the noise phase shift so as to produce a null in the signal level (or the S meter). 6. Steps 4 and 5 could be repeated to make further adjustments. There might be away to activate the control system with just one button. Does anyone know of circuits that measure audio noise? Making the RF noise canceller automatic requires an audio circuit to monitor the noise level. This noise level needs to be converted into a large DC voltage, which feeds the motors that turn the variable capacitor and potentiometer. Jason Hsu, AG4DG <a class="moz-txt-link-abbreviated" href="mailto:usenet@@@@jasonhsu.com">usenet@@@@jasonhsu.com</a> </pre> </blockquote> </body> </html> --------------000508040503080405070006--
Hi Jason


Theres a whole lot of unworkable ideas on this thread. I shouldnt rush
in without reading up well first.

I'll just address a couple of Dave's ideas.


Dave Shrader <david.shrader@comcast.net> wrote 

> Weather induced noise contains frequency components that are in the > audio passband, you can hear lightning induced static crashes in your > SSB/AM radio. How will you discriminate between desired audio and static > audio?
Lot of work was done on this in the 30s, the cnoclusion was they couldnt. However you can if you use the standard 405-line TV noise reduction method. Basically detect brief signals that are greater in amplitude than your wanted a.f., and zero or reduce the af output during that time.
> A design approach would be to use digital filtering and a series of > Kalman filters [digital filter algorithms], assuming they are available > to the general public. The Kalman filters would be tailored to the > spectral content of the noise source you are attempting to cancel. A > second design approach would be a fast Fourier transform that > discriminates N/S from S/N. You want to keep the noise OUT of the FIRST > RF STAGE to avoid pumping the AGC and getting false signals.
I dont see how you can manipulate signals that havent even reached the first rf amp. You cant even read them as theyre microvolts. Putting them thru any kind of digital filter - you work it out. Jason your idea of mixing different noise sources is also a non runner. Sorry, but youve got to consider _exactly_ what is in those noise sources and how they differ. It will soon become apparent that by the time you add them youve got 2 different things. The noise f distribution might be the same, but the noise signal will be quite different. Regards, NT
Wasn't this the basis of the TNS?

If so, it worked on impulse noise above the slow AGC level.

The ANC-4 doesn't even let the noise into the first RF stage!!

DD, W1MCE

Crazy George wrote:

> Jason: > > Very similar to what you are describing is popularly known as a "Noise > Blanker" Motorola introduced their design for mobile radios in 1959 as an > "Extender" In the same time frame, Collins offered a model for the S-Line > and KWM-2. I designed a tube model for GE's Progress Line radios, and I > forget who designed the solid state version. The concept has been described > in numerous places, so do a bibliographic search of Engineering Index, or > Scientific Abstracts, or whatever that school has access to. You also need > to familiarize yourself with the concepts involved in noise balanced > squelch, which was patented by Motorola back in the late 30s or early 40s. > It will tell you how to do the audio noise level measurement meaningfully > and apply it usefully. > > -- > Crazy George > Remove NO and SPAM from return address > "Jason Hsu" <jason_hsu@my-deja.com> wrote in message > news:f7d9a152.0308051412.54d4c913@posting.google.com... > >>THE BIG QUESTION: How do you measure the audio noise level in a >>receiver? Does anyone here know of any circuits that show the overall >>audio noise level? >> >>Let me tell you what this is all about. >> >>SIDE NOTE: Thanks again to those of you who helped me with the >>SWR/wattmeter project I worked on last semester. This project taught >>me more about ferrite cores, op amps, and diodes than ANY class >>possibly could. I learned about stray capacitance and what rails >>mean. I also learned that not all 1N34A diodes are alike. >> >>In this coming semester, I will be working on an even more ambitious >>project - an automatic noise canceller for 160m to 10m. It will >>definitely be a control system, and it may even use DSP. The device >>will also require a motor for automatically adjusting the controls. >>The idea is to design and build an automatic version of the Timewave >>ANC-4 or the MFJ-1025/1026 RF noise cancellers. >> >>The ANC-4 and MFJ-1025/1026 are manual devices. There are automatic >>noise cancellation devices, but their adjustments are at the audio >>level rather than the RF level. >> >>The back panel of my device will contain: >>1. Connector for the signal antenna >>2. Connector for the transceiver >>3. Connector for the noise antenna >>4. DC power connector >> >>The front panel of my device will contain: >>1. Power switch and the obligatory idiot light to show that the power >>is on >>2. 2 audio connectors: one connects to the transceiver, and the other >>connects to an external speaker >>3. Frequency range control for choosing the inductance values, as the >>proper inductance values in the RF noise cancelling circuit varies >>with frequency >>4. Phase range knob so that the phase shifter can cover all 360 >>degrees >>5. Manual noise phase knob >>6. Manual noise gain knob >>7. LED display to show the noise level >>8. Noise phase adjustment push-button: Pressing this button activates >>the control system to adjust the phase shift of the noise. >>9. Noise gain adjustment button: Pressing this button activates the >>control system to adjust the gain of the noise. >> >>Other features: >>1. I need to design my automatic noise canceller so that parts won't >>blow up if I transmit 100W through it. This probably requires some >>type of automatic bypass circuitry. >>2. Transmitted power must not reach the noise antenna (at least not >>without a great deal of attenuation) >>3. It also needs a low insertion loss. >>4. A preamplifier would be desirable. >> >>How it would work: >>1. You manually turn the phase and gain controls to the minimum >>settings. (Or I could put in a reset button to do that. No, that >>would add too much complexity to the circuit.) >>2. You select the band using the band inductance switch. >>3. You move the phase polarity switch to the negative setting. If >>the noise cancellation procedure does not work, it probably means the >>opposite setting is required. >>4. Press the noise gain adjustment button. The device adjusts the >>noise gain until a change in the signal level (or the S meter) is just >>noted. (Some type of derivative function would come into play.) >>5. Press the noise phase adjustment button. The device adjusts the >>noise phase shift so as to produce a null in the signal level (or the >>S meter). >>6. Steps 4 and 5 could be repeated to make further adjustments. >>There might be away to activate the control system with just one >>button. >> >>Does anyone know of circuits that measure audio noise? Making the RF >>noise canceller automatic requires an audio circuit to monitor the >>noise level. This noise level needs to be converted into a large DC >>voltage, which feeds the motors that turn the variable capacitor and >>potentiometer. >> >>Jason Hsu, AG4DG >>usenet@@@@jasonhsu.com > > > > >
Ideally you point the  noise antenna at the noise, and the signal antenna at
the signal. In the real world the noise antenna is usually fixed, but might
be pointed at something like a power line. In any case,  the noise antenna
is usually quite low, and you hope it won't pick up much of the desired
signal.

BTW, way back when, either Radio Shack or Lafayette sold a CB radio that
used a separate noise channel that was tuned to just outside the CB band. No
idea how well it worked.

Tam/WB2TT
"Brooke Clarke" <brooke@pacific.net> wrote in message
news:3F30A5BC.6050205@pacific.net...
Hi Jason:

I think the "signal antenna" and "noise antenna" are both just antennas.  I
can't see how you can make an antenna that only hears noise and another that
hears the same noise and signal.


Tweetldee wrote:
>
...
> > Now, as to your concern to keep 100W of RF from blowing up your noise > canceller. That's what antenna changeover relays are for. They normally > connect the antenna to the receiver, but when the transmitter is keyed up, > the relay connects the antenna to the transmitter output, and disconnects it > from the receiver. Simple, but effective, and has been used for many many > years in amateur as well as commercial radio equipment.
The line from the change-over relay to the receiver should be shorted when the receiver is disconnected and either short or a half wave, or else open when the receiver is disconnected and a quarter wave long. Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;