When I explain this, I use a function-generator app for my iPad. It can generate two audio functions, one on the left stereo channel and one on the right. I set them both to 1000Hz, then bump one up to 1001Hz and point out how the beat happens at exactly 1Hz by having the other guy watch the blinking colon on his digital watch. Then I bump the other down to 999Hz and show that now the beat is at 2Hz according to the watch. Then I'll try 1000.0Hz and 1000.1Hz and show how the beat now takes five seconds to rise and five seconds to fall. This sets me up for an explanation of how the beat frequency is the difference between the two mixed frequencies, and why--since RF is much higher than AF--in the case of RF the beat can be perceived as an audio-frequency whistle rather than just a rhythmic pulse. It's also good for explaining superheterodyning and intermediate frequencies, which is perfect when somebody asks how an analog-to-digital converter for a software-defined radio can possibly sample fast enough to grab a 450MHz signal. (It doesn't; the 450MHz incoming signal beats with a pristine locally-produced signal to make an intermediate-frequency signal at a few hundred kHz that's slow enough for a fast ADC to handle, but still has all the important modulations on it.) If I had better speakers on the iPad, I'd try something like 20kHz and 21kHz, to demonstrate mixing two inaudible frequencies to get an audible one, but iPad speakers suck.
Kevin, thanks for taking the time to explain this. Perhaps in a future video you can explain to fledgling cw ops why zero beat is necessary and the purpose and use of a sidetone... Dan
Thank you Kevin. Your videos are highly appreciated. I still use a Collins KWM-2 from the Vietnam era... 1962 if i recall correctly. The manuals don't explain much on the subject but being a Bass player, used the same technique to zero beat the Collins. You video explains (not visually but you mention it) how to zero beat against WWV and that I have never done it. Thanks for explaining it. 73, Rob. YS1RS
Zero beating is what piano tuners do for a living. They establish a standard first playing note "A" above middle "C" on the keyboard which should resonate at 440 hertz. They then take a tuning fork, hit it on their knee to make it vibrate, then hold it on the piano soundboard. If the sound of the tuning fork and the note "A" on the piano are out of sync or out of tune, the piano tuner will hear some faint beating. He then adjusts the strings of the piano to be in perfect sync or perfect tune with the tuning fork. When this happens, he hears no beats at all, which is called "smoothing out" or "coming in" when all three strings of the note are in tune with the tuning fork. He then, has to do something similar for all 273 strings on the piano. There are 88 keys on the piano, but most keys or notes have 3 strings per key, and some only 2 strings and the lowest bass strings have only 1 string per key. The tuner has to tune every string, sometime using an electronic device, but the best "Concert Stage Tuners" tune with their ear using "Aural Tuning Technique" meaning they rely on their ability to hear Zero Beating when tuning. This is why a good piano tuning can cost upwards of $100 (as of year 2018) and pianos should be tuned at least twice a year at seasonal changes from cold to warm weather. Pianos are very expensive, and they require expert care. Fine pianos can cost $15,000.00....PER FOOT OR MORE. A 9 foot concert grand piano can easily cost $145,000.00 No wonder we rarely see a piano in most homes, unless the family has money, or culture, or class, or musicians or all four !!
Actually the hardest part of tuning a piano is tempering the notes, which requires counting the differential beats to know that you've actually tempered the scale. A very fine skill.
Kevin, wasn't trying to bust your chops. It also seemed you were dealing with a stuffy head cold at the time. I have really appreciated your channel, especially the ones dealing with Linux and sound card digital modes. Keep up the good work.73, kd5ssj
I enjoyed this video Kevin thanks for doing it. with FM radios we do something similar inject the IF frequency with a generator and a second generator on the carrier frequency adjust for a zero beat. Well this was back in the day of crystals and channel elements in radio 73's Don
I think instead of doing what you did with that static in the video, you should have done what you talked about at the end, with the WWV 10 MHz signal, would have helped me understand it more. thanks though.
Yep, but I was talking about the frequency standards.. Rubidium was what I was trying to remember. Dave Jones did a nice teardown of one of them... You can actually find them on ebay, surplus from cell phone towers I think. ua-cam.com/video/I55uLRRvLCU/v-deo.html
Kevin Loughin, by the way, great to hear the HW7 wake up! The rig works very well; it just lives in that bullet-riddled home. Cannot wait to see you repackage it. Will get the receiver upgrade mods to you ASAP. dit dit, Bill
What are you measuring the beat of the two signals on for reference to check a standard? I'm wondering how to check a local oscillator against WWV or similar for calibration purposes. I understand hetrodyning and so forth. I'm wondering about the connections etc. WWV uses rubidium standard, as this is what is used as an atomic standard. I'm just wondering how to measure the phase difference. I'm not sure as I don't have a TRF radio only superhetrodyne single conversion. Mine does not have a BFO for code reception. I have a fair amount of test equipment, and know about calibration with a standard, but not sure how to check my standard against a radio signal. BTW the atomic clock was even in an article in Electronics world some years ago before it became Popular electronics in the 1970's. Some of the most complex things are obvious to me, but this one.
Thank you! I always wanted a good explanation of this phenomenon. Question, In any way, does this relate to the sound you hear in a moving car that gets cancelled when you crack a window? TU De Dave K3FT
I don't think so. I'd guess that with the windows closed, air pressure in the car is changing slightly and rapidly and outside air pushes in through the vents. Opening a window would smooth out those pressure changes. That low frequency throb sound is what I'm thinking about.
New ham here. As I’m tuning along the bands on my local club’s HF radio in either SSB or CB, I’ll often run across random “tones” coming into my receiver. Not beacons, they never transmit any Morse code, just a continuous tone. I’ve wondered if this could possibly be a carrier wave for some blank transmission, as I don’t hear them in AM mode but I can still hear the slight increase in the amplitude of the general noise you hear, but I hear many of these and I couldn’t see why there would be that many random blank transmissions. Any idea if it could be something related to this?
There's many noise sources in a modern building or house. Ethernet network cabling will produce those tones, sometimes they warble just a slight bit. Power supplies, plug-in chargers for devices, TV sets, all kinds of things will produce interference noise.
Kevin, I think that you interchanged the use of mixing and arithmetic addition. You can't zero beat through the audio amp and/or your ear, neither can pass DC (hence zero-beat) which is what you get when the two signals are perfectly in sync. Using the S-meter will get you even closer to zero, but not perfect. For the time and frequency nuts in your audience see Don Kirk's WD8DSB article in Feb. 2017 QST, pg 41. Your generators also appeared to injection lock, based on the oscilloscope pictures.
Well Cash, this video was more of a demystifying educational bit for new hams. We weren't going for the lab quality high science of the matter. ;-) Signal source was an old heathkit signal generator, so nothing fancy there. Thanks for the additional info though, I'm sure there are a few viewers that will find that article reference quite useful!
I'm a little confused. A BFO is used to beat against a carrier to produce an audible tone, say 600 Hz. And then another sidetone(or spot button) of 600 Hz is mixed with this audible tone to produce a zero beat? Is this even close? Thank you!😁
I sort of understood zero beating, but seeing it on the scope, made it all come together.
Thanks, KE0JWK
When I explain this, I use a function-generator app for my iPad. It can generate two audio functions, one on the left stereo channel and one on the right. I set them both to 1000Hz, then bump one up to 1001Hz and point out how the beat happens at exactly 1Hz by having the other guy watch the blinking colon on his digital watch. Then I bump the other down to 999Hz and show that now the beat is at 2Hz according to the watch. Then I'll try 1000.0Hz and 1000.1Hz and show how the beat now takes five seconds to rise and five seconds to fall.
This sets me up for an explanation of how the beat frequency is the difference between the two mixed frequencies, and why--since RF is much higher than AF--in the case of RF the beat can be perceived as an audio-frequency whistle rather than just a rhythmic pulse.
It's also good for explaining superheterodyning and intermediate frequencies, which is perfect when somebody asks how an analog-to-digital converter for a software-defined radio can possibly sample fast enough to grab a 450MHz signal. (It doesn't; the 450MHz incoming signal beats with a pristine locally-produced signal to make an intermediate-frequency signal at a few hundred kHz that's slow enough for a fast ADC to handle, but still has all the important modulations on it.)
If I had better speakers on the iPad, I'd try something like 20kHz and 21kHz, to demonstrate mixing two inaudible frequencies to get an audible one, but iPad speakers suck.
Thank you for this clear and methodical explanation -- I was excited to learn what the squealing noises are when you're trying to tune in a radio!
Kevin, thanks for taking the time to explain this. Perhaps in a future video you can explain to fledgling cw ops why zero beat is necessary and the purpose and use of a sidetone... Dan
As a new ham, I thought this really was a great explanation! Thanks.
Thank you Kevin. Your videos are highly appreciated. I still use a Collins KWM-2 from the Vietnam era... 1962 if i recall correctly. The manuals don't explain much on the subject but being a Bass player, used the same technique to zero beat the Collins. You video explains (not visually but you mention it) how to zero beat against WWV and that I have never done it. Thanks for explaining it. 73, Rob. YS1RS
Zero beating is what piano tuners do for a living. They establish a standard first playing note "A" above middle "C" on the keyboard which should resonate at 440 hertz. They then take a tuning fork, hit it on their knee to make it vibrate, then hold it on the piano soundboard. If the sound of the tuning fork and the note "A" on the piano are out of sync or out of tune, the piano tuner will hear some faint beating. He then adjusts the strings of the piano to be in perfect sync or perfect tune with the tuning fork. When this happens, he hears no beats at all,
which is called "smoothing out" or "coming in" when all three strings of the note are in tune with the tuning fork. He then, has to do something similar for all 273 strings on the piano. There are 88 keys on the piano, but most keys or notes have 3 strings per key, and some only 2 strings and the lowest bass strings have only 1 string per key.
The tuner has to tune every string, sometime using an electronic device, but the best "Concert Stage Tuners" tune with their ear using "Aural Tuning Technique" meaning they rely on their ability to hear Zero Beating when tuning. This is why a good piano tuning can cost upwards of $100 (as of year 2018) and pianos should be tuned at least twice a year at seasonal changes from cold to warm weather.
Pianos are very expensive, and they require expert care. Fine pianos can cost $15,000.00....PER FOOT OR MORE. A 9 foot concert grand piano can easily cost $145,000.00 No wonder we rarely see a piano in most homes, unless the family has money, or culture, or class, or musicians or all four !!
Actually the hardest part of tuning a piano is tempering the notes, which requires counting the differential beats to know that you've actually tempered the scale. A very fine skill.
Kevin, wasn't trying to bust your chops. It also seemed you were dealing with a stuffy head cold at the time. I have really appreciated your channel, especially the ones dealing with Linux and sound card digital modes. Keep up the good work.73, kd5ssj
I enjoyed this video Kevin thanks for doing it. with FM radios we do something similar inject the IF frequency with a generator and a second generator on the carrier frequency adjust for a zero beat. Well this was back in the day of crystals and channel elements in radio 73's Don
Good job on explaining the concept of zero-beating. It's a really tough subject to explain. 73 de K7RMJ Frank
Nice little scope, I just bought a hantek and love it so far
Thankyou. Great explanation.
Musicians use zero beating all the time. It's how you get in tune with each other.
We sure do!
Awesome tutorial
Thank you. Very interesting.
Excellent ...Thank you.......
thanks nicely explained
thank you. added for future reference.
I think instead of doing what you did with that static in the video, you should have done what you talked about at the end, with the WWV 10 MHz signal, would have helped me understand it more. thanks though.
Kevin, it's a cesium clock at NIST in CO and HI.
73
Bill, k6whp
Yep, but I was talking about the frequency standards.. Rubidium was what I was trying to remember.
Dave Jones did a nice teardown of one of them... You can actually find them on ebay, surplus from cell phone towers I think.
ua-cam.com/video/I55uLRRvLCU/v-deo.html
Kevin Loughin, by the way, great to hear the HW7 wake up! The rig works very well; it just lives in that bullet-riddled home. Cannot wait to see you repackage it. Will get the receiver upgrade mods to you ASAP.
dit dit,
Bill
What are you measuring the beat of the two signals on for reference to check a standard? I'm wondering how to check a local oscillator against WWV or similar for calibration purposes. I understand hetrodyning and so forth. I'm wondering about the connections etc. WWV uses rubidium standard, as this is what is used as an atomic standard. I'm just wondering how to measure the phase difference. I'm not sure as I don't have a TRF radio only superhetrodyne single conversion. Mine does not have a BFO for code reception. I have a fair amount of test equipment, and know about calibration with a standard, but not sure how to check my standard against a radio signal. BTW the atomic clock was even in an article in Electronics world some years ago before it became Popular electronics in the 1970's. Some of the most complex things are obvious to me, but this one.
Thanks Kevin, do you know a way
to show wwv carrier wave or any other radio carrier wave on an oscilloscope?
Thank you! I always wanted a good explanation of this phenomenon. Question, In any way, does this relate to the sound you hear in a moving car that gets cancelled when you crack a window? TU De Dave K3FT
I don't think so. I'd guess that with the windows closed, air pressure in the car is changing slightly and rapidly and outside air pushes in through the vents. Opening a window would smooth out those pressure changes. That low frequency throb sound is what I'm thinking about.
New ham here. As I’m tuning along the bands on my local club’s HF radio in either SSB or CB, I’ll often run across random “tones” coming into my receiver. Not beacons, they never transmit any Morse code, just a continuous tone. I’ve wondered if this could possibly be a carrier wave for some blank transmission, as I don’t hear them in AM mode but I can still hear the slight increase in the amplitude of the general noise you hear, but I hear many of these and I couldn’t see why there would be that many random blank transmissions. Any idea if it could be something related to this?
There's many noise sources in a modern building or house. Ethernet network cabling will produce those tones, sometimes they warble just a slight bit. Power supplies, plug-in chargers for devices, TV sets, all kinds of things will produce interference noise.
Kevin, I think that you interchanged the use of mixing and arithmetic addition. You can't zero beat through the audio amp and/or your ear, neither can pass DC (hence zero-beat) which is what you get when the two signals are perfectly in sync. Using the S-meter will get you even closer to zero, but not perfect. For the time and frequency nuts in your audience see Don Kirk's WD8DSB article in Feb. 2017 QST, pg 41. Your generators also appeared to injection lock, based on the oscilloscope pictures.
Well Cash, this video was more of a demystifying educational bit for new hams. We weren't going for the lab quality high science of the matter. ;-) Signal source was an old heathkit signal generator, so nothing fancy there.
Thanks for the additional info though, I'm sure there are a few viewers that will find that article reference quite useful!
Hey couldn't you use this to tune the offset of an SDR? This is an older video and maybe you've answered it in another video.
Sure. Feed it an accurate carrier and put the SDR software into USB mode.
How does complete a RADAR pulse repetition frequency (PRF) in zero beat to obtain a truth PFF which generated by a radar?
I'm a little confused. A BFO is used to beat against a carrier to produce an audible tone, say 600 Hz. And then another sidetone(or spot button) of 600 Hz is mixed with this audible tone to produce a zero beat? Is this even close? Thank you!😁
Doesn't your scope do addition?
Yeah, I think so. I didn't dig that far into it. It was my assistants day off.
That puts your recieve on freq but how about your transmit?
If you have a separate transmitter, just feed it into a dummy load and key down then tune it to zero beat with your receiver I guess.
21Jun2017 - another one just showed up.
My wife thought zero-beat meant you weren’t musically-inclined lol
Cesium.