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What does zero-beat sound like? #ubitx

 

Ok this might be the most newbie queastion in the century but I am not sure what Farhan means in the Tune-Up instructions to calibrate the uBitx to "zero-beat" on a known AM station.
Doest this mean turning for best sound? No sound? A 1000rz tone?
Seriously what is this "zero beat" on an AM broadcast station supposed to sound like ?-)


Thanks!


Rogier
 

Rogier

Have you ever tuned across a steady carrier with a CW receiver and listened to the tone
as it starts high (difference between the two signals), then goes lower as you get closer to
the same frequency, and then goes back higher as you move to a higher difference between
signal frequencies?? Near the center of this tuning range the difference signal will go lower
and lower until it becomes less than 1 Hz.? If your receiver has an S-meter you can probably
see the meter waving back and forth at a few tenths of Hz difference.? Continue fine tuning to
minimize this slow frequency difference and you will find a place where there is no difference
between LO+/- BFO and received signal.? That is "Zero-Beat".? I guess the term "zero" means
"no beat note"...maybe...?

Hope that helps.
Sometimes us ancient old geezers assume that newer hams already know all the radio language.

Arv? K7HKL
_._


On Tue, May 29, 2018 at 4:14 PM kj6etl <pa1zz@...> wrote:
Ok this might be the most newbie queastion in the century but I am not sure what Farhan means in the Tune-Up instructions to calibrate the uBitx to "zero-beat" on a known AM station.
Doest this mean turning for best sound? No sound? A 1000rz tone?
Seriously what is this "zero beat" on an AM broadcast station supposed to sound like ?-)


Thanks!


Rogier

 

When tuning in an AM station when your rig is listening on SSB, you will hear a carrier tone... This will vary depending on whether you change your frequency up or down... When you tune so that the frequency you hear gets so low that it "disappears" then you have "zero-beated" on the station... Most commercial rigs have a tune button that typically is at every 25 or 100 khz on the dial...

Once you no longer hear the tone then that's when you calibrate your dial... A good frequency on air is WWV @ 10.000Mhz...

I hope that helps,

Glenn VE3JAU


On Tue, May 29, 2018 at 6:11 PM, kj6etl <pa1zz@...> wrote:
Ok this might be the most newbie queastion in the century but I am not sure what Farhan means in the Tune-Up instructions to calibrate the uBitx to "zero-beat" on a known AM station.
Doest this mean turning for best sound? No sound? A 1000rz tone?
Seriously what is this "zero beat" on an AM broadcast station supposed to sound like ?-)


Thanks!


Rogier


 

Hi Arv,

Thanks again!

Yes I am an old ham myself by now and am familliar with the turning across a CW signal ;-)

Problem is that the uBitx doesnt have an s meter so your advice is hard to implement. So should the new ham tune for best audio or what ?-)

Alternatively I can ask a friend to transmit in SSB or CW so I can calibrate to that.
Now the question is should he transmit in CW or the appropriate sideband for that frequency?
I don't know what in what mode the calibration is taking place and using the wrong sideband could cause the rig to be off by a couple of khz..


Hoping this will also serve other people who might be puzzled with the instructions..

Smiles across the wires,

Rogier
 

Rogier KJ6ETL

Might also mention that if you are zero-beating against WWVB or WWVH there is
modulation on the carrier that will interfere with getting a proper zero-beat.? This
modulation is shut off at 43 minutes past the hour and turned on again 52 minutes
after the hour.??
This means that to get a true zero-beat you need to do it between 43 minutes after
the hour and 52 minutes after the hour.


On Tue, May 29, 2018 at 4:30 PM Arv Evans <arvid.evans@...> wrote:
Rogier

Have you ever tuned across a steady carrier with a CW receiver and listened to the tone
as it starts high (difference between the two signals), then goes lower as you get closer to
the same frequency, and then goes back higher as you move to a higher difference between
signal frequencies?? Near the center of this tuning range the difference signal will go lower
and lower until it becomes less than 1 Hz.? If your receiver has an S-meter you can probably
see the meter waving back and forth at a few tenths of Hz difference.? Continue fine tuning to
minimize this slow frequency difference and you will find a place where there is no difference
between LO+/- BFO and received signal.? That is "Zero-Beat".? I guess the term "zero" means
"no beat note"...maybe...?

Hope that helps.
Sometimes us ancient old geezers assume that newer hams already know all the radio language.

Arv? K7HKL
_._


On Tue, May 29, 2018 at 4:14 PM kj6etl <pa1zz@...> wrote:
Ok this might be the most newbie queastion in the century but I am not sure what Farhan means in the Tune-Up instructions to calibrate the uBitx to "zero-beat" on a known AM station.
Doest this mean turning for best sound? No sound? A 1000rz tone?
Seriously what is this "zero beat" on an AM broadcast station supposed to sound like ?-)


Thanks!


Rogier

 

I have no idea what the various software releases for the uBitx are doing.
But during calibration, the BFO should be placed in the center of the 12mhz crystal filter?
so a zero beat can be heard.

Also, the accuracy of that zero beat is proportional to the frequency of the signal.
So a zero beat to WWV at 15mhz is 15 times more accurate than a zero beat of a 1.0mhz AM broadcast station.
The three local oscillators are each a strict ratio of the 25mhz reference,? ?and from post 44515
the operating frequency of a stock uBitx in LSB mode is:? ? vfo - (clk1-bfo)?
By the distributive law of algebra, a 100ppm change in vfo, clk1 and bfo will result in a 100ppm change in the operating frequency.

Jerry


On Tue, May 29, 2018 at 03:38 pm, Glenn Anderson wrote:
When tuning in an AM station when your rig is listening on SSB, you will hear a carrier tone... This will vary depending on whether you change your frequency up or down... When you tune so that the frequency you hear gets so low that it "disappears" then you have "zero-beated" on the station... Most commercial rigs have a tune button that typically is at every 25 or 100 khz on the dial...

Once you no longer hear the tone then that's when you calibrate your dial... A good frequency on air is WWV @ 10.000Mhz...

I hope that helps,

Glenn VE3JAU
 

Rojier,

I am tempted to reply "the sound of one hand clapping" but that would only be partially true. You hit the nail squarely when you surmised the best sound on an AM station. When you tune so that the carrier decreases in frequency to the point to where it can no longer be heard then you are approaching zero beat. Now if you listen to the modulation content, particularly if it is music, you continue to tune for the most natural sound. If you have an ear for music, there will be a point where everything is "in tune". That's the point where you are truly tuned to frequency. Some folks can pick up just a Hertz or two! 73, Don
 

Hi Don,

Thank you for confirming this!

I purposely asked the questions as uninformed as possible. I was assuming the best sound would be zero beat but given the fact that this uBitx has thrown me a couple of curve balls I stated to doubth myself and was looking for a confirmation on my assumption ;-)

There are quite a few errors and assumptions in the manual that are easilly been overlooked by those who grew up with this project or are wizards of the eletrons. Hoping that this little tread might help.

Smiles across the wires,

Rogier
Mike aka KC2WVB
 

Just a thought:

?It seems to me to be without question that if one were to allign/adjust/tune an oscillator to a precise frequency by listening for a zero beat with respect to a known reference frequency that the higher the reference frequency the greater the accuracy with respect to alignment of the oscillator. However, if done by human ear the entire procedure is only as precise as the individual's ability to detect the a a absence of low frequency audio signals. So for someone like me who has been yelled at by kid's, dogs and other assorted life forms for 63 years the theoretical may be a bit of a moot point?

On May 29, 2018 6:58 PM, "Jerry Gaffke via Groups.Io" <jgaffke=[email protected]> wrote:
I have no idea what the various software releases for the uBitx are doing.
But during calibration, the BFO should be placed in the center of the 12mhz crystal filter?
so a zero beat can be heard.

Also, the accuracy of that zero beat is proportional to the frequency of the signal.
So a zero beat to WWV at 15mhz is 15 times more accurate than a zero beat of a 1.0mhz AM broadcast station.
The three local oscillators are each a strict ratio of the 25mhz reference,? ?and from post 44515
the operating frequency of a stock uBitx in LSB mode is:? ? vfo - (clk1-bfo)?
By the distributive law of algebra, a 100ppm change in vfo, clk1 and bfo will result in a 100ppm change in the operating frequency.

Jerry


On Tue, May 29, 2018 at 03:38 pm, Glenn Anderson wrote:
When tuning in an AM station when your rig is listening on SSB, you will hear a carrier tone... This will vary depending on whether you change your frequency up or down... When you tune so that the frequency you hear gets so low that it "disappears" then you have "zero-beated" on the station... Most commercial rigs have a tune button that typically is at every 25 or 100 khz on the dial...

Once you no longer hear the tone then that's when you calibrate your dial... A good frequency on air is WWV @ 10.000Mhz...

I hope that helps,

Glenn VE3JAU
 

The 30x improvement by calibrating at 30mhz vs calibrating at 1mhz is not theoretical,
even if your hearing is shot.
Instead of looking for a 10hz change in tone, you are looking for a 300hz change.

The ideal might be to monitor the audio from a Nano analog pin, have it look?
for either zero-beat or a specific tone.? Especially for those like me who are tone deaf.

With FFT's on an ARM processor like the Teensy, could discriminate the carrier from
the audio tones on WWV.



On Thu, May 31, 2018 at 08:02 am, Mike aka KC2WVB wrote:
?It seems to me to be without question that if one were to allign/adjust/tune an oscillator to a precise frequency by listening for a zero beat with respect to a known reference frequency that the higher the reference frequency the greater the accuracy with respect to alignment of the oscillator. However, if done by human ear the entire procedure is only as precise as the individual's ability to detect the a a absence of low frequency audio signals. So for someone like me who has been yelled at by kid's, dogs and other assorted life forms for 63 years the theoretical may be a bit of a moot point?
?
 

On Thu, 31 May 2018 11:02:34 -0400
"Mike aka KC2WVB" <rb5363@...> wrote:

Just a thought:

It seems to me to be without question that if one were to
allign/adjust/tune an oscillator to a precise frequency by listening
for a zero beat with respect to a known reference frequency that the
higher the reference frequency the greater the accuracy with respect
to alignment of the oscillator. However, if done by human ear the
entire procedure is only as precise as the individual's ability to
detect the a a absence of low frequency audio signals. So for someone
like me who has been yelled at by kid's, dogs and other assorted life
forms for 63 years the theoretical may be a bit of a moot point?

On May 29, 2018 6:58 PM, "Jerry Gaffke via Groups.Io" <jgaffke=
[email protected]> wrote:

I have no idea what the various software releases for the uBitx are
doing. But during calibration, the BFO should be placed in the center
of the 12mhz crystal filter
so a zero beat can be heard.

Also, the accuracy of that zero beat is proportional to the frequency
of the signal.
So a zero beat to WWV at 15mhz is 15 times more accurate than a zero
beat of a 1.0mhz AM broadcast station.
The three local oscillators are each a strict ratio of the 25mhz
reference, and from post 44515
the operating frequency of a stock uBitx in LSB mode is: vfo -
(clk1-bfo)
By the distributive law of algebra, a 100ppm change in vfo, clk1 and
bfo will result in a 100ppm change in the operating frequency.

Jerry

I have used an analog voltmeter on the speaker leads to watch the beat
tone. You just watch the meter move as you tune toward zero-beat. It
will move up and down at a slower and slower pace. You can get pretty
darn close to zero-beat this way. The biggest problem is that the SSB
filter causes a drop-off at the lower frequencies making the beat tone
disappear. You kind of have to interpolate even with the meter.

If you have a third receiver you might be able to transmit a CW signal
from the ubitx against a strong external signal that is a known
frequency and use the 3rd receiver to listen to the beat tone between
the external signal and your ubitx. You can tell just how far your
calibration is off in that manner. In fact that is kind of what the
"spot" function on many older transmitters was for. You could
"zero-beat" your transmitter using a low-power output against a station
you wanted to talk to.

tim ab0wr

On Tue, May 29, 2018 at 03:38 pm, Glenn Anderson wrote:

When tuning in an AM station when your rig is listening on SSB, you
will hear a carrier tone... This will vary depending on whether you
change your frequency up or down... When you tune so that the
frequency you hear gets so low that it "disappears" then you have
"zero-beated" on the station... Most commercial rigs have a tune
button that typically is at every 25 or 100 khz on the dial...

Once you no longer hear the tone then that's when you calibrate your
dial... A good frequency on air is WWV @ 10.000Mhz...

I hope that helps,

Glenn VE3JAU
Mike aka KC2WVB
 

Interesting, I will have to look at this at a level that is more than casual. I was thinking that one would be discriminating to the limit of zero Hz.

I do like the idea of the Nano or Uno or... serving as the measuring instrument because I am tone death too.

On Thu, May 31, 2018, 11:16 AM Jerry Gaffke via Groups.Io <jgaffke=[email protected]> wrote:
The 30x improvement by calibrating at 30mhz vs calibrating at 1mhz is not theoretical,
even if your hearing is shot.
Instead of looking for a 10hz change in tone, you are looking for a 300hz change.

The ideal might be to monitor the audio from a Nano analog pin, have it look?
for either zero-beat or a specific tone.? Especially for those like me who are tone deaf.

With FFT's on an ARM processor like the Teensy, could discriminate the carrier from
the audio tones on WWV.



On Thu, May 31, 2018 at 08:02 am, Mike aka KC2WVB wrote:
?It seems to me to be without question that if one were to allign/adjust/tune an oscillator to a precise frequency by listening for a zero beat with respect to a known reference frequency that the higher the reference frequency the greater the accuracy with respect to alignment of the oscillator. However, if done by human ear the entire procedure is only as precise as the individual's ability to detect the a a absence of low frequency audio signals. So for someone like me who has been yelled at by kid's, dogs and other assorted life forms for 63 years the theoretical may be a bit of a moot point?
?
 

Easy enough to place the BFO at the center of the 12mhz crystal filter,
then the near zero hz beat comes through strong as ever.
In the equations of post? ??/g/BITX20/message/44278
just set the value of "pbt" to zero.

There is capacitive coupling through the audio chain that will attenuate
those extremely low frequencies, that may need to be adjusted somehow.


On Thu, May 31, 2018 at 09:02 am, Tim Gorman wrote:
The biggest problem is that the SSB
filter causes a drop-off at the lower frequencies making the beat tone
disappear. You kind of have to interpolate even with the meter.
 

¿ªÔÆÌåÓý

You can¡¯t discriminate down to zero Hz unless you tap off at the right point with a DC amplifier. ?The AC coupling provides a high pass filter that will block the signal above some frequency.

I built a number of digital clocks, back when LSI chips came out to support it. ?Most of the clocks I but used the AC line for the timing reference but I built one that was battery powered. ?Initially I used an NE555 timer for the timing. ?I zero beat it with the AC line using an analog VOM connected between an transformer and the NE555. ?As I adjust the frequency the meter needle would start swinging back and forth at the beat frequency (once the beat frequency dropped low enough). ?Then I could adjust it till the meter slowed and eventually stopped. ?

The 555 provide to be a reasonably stable clock. ?Later I switched to a crystal derived clock.



Clark Martin
KK6ISP

On May 31, 2018, at 9:02 AM, Mike aka KC2WVB <rb5363@...> wrote:

Interesting, I will have to look at this at a level that is more than casual. I was thinking that one would be discriminating to the limit of zero Hz.

I do like the idea of the Nano or Uno or... serving as the measuring instrument because I am tone death too.
Mike aka KC2WVB
 

OK, that makes sense. I am reading the comments between shopping stops.

I really had not looked at it, initially, beyond superficially and was kind of just spitting out an intuitive thought.?

I find the algebraic combination of distinct signals to be rather interesting. I remember doing a lot of similar work, long ago, while a grad student and partaking in a class related to partial differential equations although it was less about application and more about showing the validity of the tools. Incidentally if you should ever want to watch a Fourier Series take the shape of the function it constructs across a specified interval find a copy of the software called "Maple." Maple will allow you to take a finite summation from the infinite series and plot it in such a way that the result looks like a movie or animation of the birth of the targeted function. Besides being neat to witness it is rather instructive too.


On Thu, May 31, 2018, 1:23 PM Clark Martin <kk6isp@...> wrote:
You can¡¯t discriminate down to zero Hz unless you tap off at the right point with a DC amplifier.? The AC coupling provides a high pass filter that will block the signal above some frequency.

I built a number of digital clocks, back when LSI chips came out to support it.? Most of the clocks I but used the AC line for the timing reference but I built one that was battery powered.? Initially I used an NE555 timer for the timing.? I zero beat it with the AC line using an analog VOM connected between an transformer and the NE555.? As I adjust the frequency the meter needle would start swinging back and forth at the beat frequency (once the beat frequency dropped low enough).? Then I could adjust it till the meter slowed and eventually stopped. ?

The 555 provide to be a reasonably stable clock.? Later I switched to a crystal derived clock.



Clark Martin
KK6ISP

On May 31, 2018, at 9:02 AM, Mike aka KC2WVB <rb5363@...> wrote:

Interesting, I will have to look at this at a level that is more than casual. I was thinking that one would be discriminating to the limit of zero Hz.

I do like the idea of the Nano or Uno or... serving as the measuring instrument because I am tone death too.
 

I'm wondering if a multimeter on the (non-decoupled) audio might show it better. Measure AC, then DC. AC will register level down to say 10, maybe 5Hz, and DC (particularly analog-needle) will show variation by swing down to 0.1Hz? (10 seconds per swing).
Disclaimer: untried, but 'worth a crack, Nigel'? Purely theoretical, where would that be best measured?
73
Dex, ZL2DEX
Mike aka KC2WVB
 

OK, I thought about this can of worms I opened on the ride home. Given the stores are 60 miles from the mountain top home I am staying at this summer I had roughly 45 minutes to sort through the various responses.

First, we should agree that the metric that establishes the accuracy one is aiming for is wave? lenght. Wave length of course is the distance propagated in one complete cycle. So Jerry is correct in that if your aim is to set an oscillator at a set frequency then being off by as much as 300 hz when using? a 30 MHz signal as a reference is equivalent to being off by 10 hz when using a 1 Mhz signal as a? reference. This is due to 10 cycles at 1Mhz and 300 cycles at 30 Mhz, when viewed as occupying distance, are equal in lenght.

If I have bad hearing it is normally at the low or high end of the spectrum and what Jerry pointed out shows that I can still obtain the accuracy of someone with better hearing by using a higher frequency for a reference signal and if our hearing is equivalent then I simply obtain higher accuracy by using the higher frequency reference signal.

As the other gentleman pointed out being able to have accuracy that resolves to perfection is most likely not even possible because of capacitor issues that end up blocking or at least attenuating the lowest of the lows in terms of audio signals.

However, I do disagree with defining theoretical so as to indicate other than actual conditions for while the theoretical and actual may not coincide there are times that they do.

Thank you all for chipping in to this discussion brought on by my thinking out loud. Its been interesting.

On Thu, May 31, 2018, 4:55 PM Dexter N Muir <dexy@...> wrote:

I'm wondering if a multimeter on the (non-decoupled) audio might show it better. Measure AC, then DC. AC will register level down to say 10, maybe 5Hz, and DC (particularly analog-needle) will show variation by swing down to 0.1Hz? (10 seconds per swing).
Disclaimer: untried, but 'worth a crack, Nigel'? Purely theoretical, where would that be best measured?
73
Dex, ZL2DEX
 

More from the thinkery, Mike:

TP20 should give a good meter point. There's a 0.1uF to earth there, but at low freq and Z its Z won't affect much.
..and theoretical, 'cos I don't actually have one: stalled with bitx-40 and horrific QRM at the QTH :( .

73
Dex, ZL2DEX
 

I tried the "official" calibration routine, but turned out to be VERY rough.

Two reasons for this:

a) Zero beating with loudspeaker or earphones requires that these two transducers can reproduce split-Hz tones, plus your ears can detect them.

b) The offered by the firmware calibration values are very wide.

?

What did I do after this:

1) Selected by ear two calibration values that sounded as the "best" pair in regards to zero beating.

2) Used them both and the WSJT-x software, in calibration mode, to find the two offsets (one positive the other negative if you have done a good zero beating job)

3) With the aid of the CEC manager, read the internal long calibration parameter for both cases.

4) Interpolated parameters of 3) with offsets from 2) and wrote (i.e. programmed) the new value a bit rounded, as it doesn't make any sense to seek more accuracy that the master clock's stability allows.

?

73 Nikos

 

The tuning is close for those that do not have test equipment.

What I usually do is set a sideband rig readout either 1000 hz higher or lower than the desired frequency depending on the sideband .? Then feed it a signal that is on frequency and put a counter on the speaker.? When the speaker output is 1000 hz, then the receiver is set.? No guessing about trying to hear the zero beat below around 100 hz or less.

While I bought used test equipment and do not have that much in it, here I set with a $ 120 rig and use about? $ 5000 worth of test equipment to set it with.
Would have been much less expensive to buy a transceiver already to go..But I would not have nearly as much fun working with this little rig.?

As I see it, Mr. Farhan did an excellent job of making an inexpensive rig for those that can not afford a more expensive rig, and for those of us that like to tinker with items that we do not have the skill or way to make the circuit boards and such from scratch.?
+
de ku4pt




On Thu, May 31, 2018 at 5:11 PM, Mike aka KC2WVB <rb5363@...> wrote:
OK, I thought about this can of worms I opened on the ride home. Given the stores are 60 miles from the mountain top home I am staying at this summer I had roughly 45 minutes to sort through the various responses.

First, we should agree that the metric that establishes the accuracy one is aiming for is wave? lenght. Wave length of course is the distance propagated in one complete cycle. So Jerry is correct in that if your aim is to set an oscillator at a set frequency then being off by as much as 300 hz when using? a 30 MHz signal as a reference is equivalent to being off by 10 hz when using a 1 Mhz signal as a? reference. This is due to 10 cycles at 1Mhz and 300 cycles at 30 Mhz, when viewed as occupying distance, are equal in lenght.

If I have bad hearing it is normally at the low or high end of the spectrum and what Jerry pointed out shows that I can still obtain the accuracy of someone with better hearing by using a higher frequency for a reference signal and if our hearing is equivalent then I simply obtain higher accuracy by using the higher frequency reference signal.

As the other gentleman pointed out being able to have accuracy that resolves to perfection is most likely not even possible because of capacitor issues that end up blocking or at least attenuating the lowest of the lows in terms of audio signals.

However, I do disagree with defining theoretical so as to indicate other than actual conditions for while the theoretical and actual may not coincide there are times that they do.

Thank you all for chipping in to this discussion brought on by my thinking out loud. Its been interesting.

_._,_._,_

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