AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency

Michael A. Terrell wrote:
> isw wrote:
>>
>> That particular receiver doesn't have much of a "front end"; diodes
>> (with protection) and straight into the first mixer. No RF stage, tuned
>> or otherwise.
>
> It can exceed the PIV of the protection diodes and cause them to
> short, or explode. That crappy Sony design is where the harmonics came
> from. The diodes, (or any other semiconductor) with enough RF can
> generate a lot of spurious signals. It can even come from a rusty joint
> in the area.

Is the ICF-SW7600GR significantly better performing
than the ICF-7600D on this?

gr, Hein

"Ron Baker, Pluralitas!" <this@aint.me> wrote in message news:469db833$0$20583
> "Hein ten Horn" <tenhornRemovE@ThiSraketnet.nl> wrote in message
>> "Ron Baker, Pluralitas!" <this@aint.me> wrote in message
>>> "Hein ten Horn" <tenhornRemovE@ThiSraketnet.nl> wrote in message
>>>> Ron Baker, Pluralitas! wrote:
>>>>> "Hein ten Horn" wrote:
>>>>>> Ron Baker, Pluralitas! wrote:
>>>>>>> Hein ten Horn wrote:
>>>>>>>> Ron Baker, Pluralitas! wrote:
>>>>>>>>> Hein ten Horn wrote:
>>>>>>
>>>>>>>>>> As a matter of fact the resulting force (the resultant) is
>>>>>>>>>> fully determining the change of the velocity (vector) of
>>>>>>>>>> the element.
>>>>>>>>>> The resulting force on our element is changing at the
>>>>>>>>>> frequency of 222 Hz, so the matter is vibrating at the
>>>>>>>>>> one and only 222 Hz.
>>>>>>>>>
>>>>>>>>> Your idea of frequency is informal and leaves out
>>>>>>>>> essential aspects of how physical systems work.
>>>>>>>>
>>>>>>>> Nonsense. Mechanical oscillations are fully determined by
>>>>>>>> forces acting on the vibrating mass. Both mass and resulting force
>>>>>>>> determine the frequency. It's just a matter of applying the laws of
>>>>>>>> physics.
>>>>>>>
>>>>>>> You don't know the laws of physics or how to apply them.
>>>>>>
>>>>>> I'm not understood. So, back to basics.
>>>>>> Take a simple harmonic oscillation of a mass m, then
>>>>>> x(t) = A*sin(2*pi*f*t)
>>>>>> v(t) = d(x(t))/dt = 2*pi*f*A*cos(2*pi*f*t)
>>>>>> a(t) = d(v(t))/dt = -(2*pi*f)^2*A*sin(2*pi*f*t)
>>>>>> hence
>>>>>> a(t) = -(2*pi*f)^2*x(t)
>>>>>
>>>>> Only for a single sinusoid.
>>>>>
>>>>>> and, applying Newton's second law,
>>>>>> Fres(t) = -m*(2*pi*f)^2*x(t)
>>>>>> or
>>>>>> f = ( -Fres(t) / m / x(t) )^0.5 / (2pi).
>>>>>
>>>>> Only for a single sinusoid.
>>>>> What if x(t) = sin(2pi f1 t) + sin(2pi f2 t)
>>>>
>>>> In the following passage I wrote "a relatively
>>>> slow varying amplitude", which relates to the
>>>> 4 Hz beat in the case under discussion (f1 =
>>>> 220 Hz and f2 = 224 Hz) where your
>>>> expression evaluates to
>>>> x(t) = 2 * cos(2pi 2 t) * sin(2pi 222 t),
>>>> indicating the matter is vibrating at 222 Hz.
>>>
>>> So where did you apply the laws of physics?
>>> You said, "It's just a matter of applying the laws of
>>> physics." Then you did that for the single sine case. Where
>>> is your physics calculation for the two sine case?
>>> Where is the expression for 'f' as in your first
>>> example? Put x(t) = 2 * cos(2pi 2 t) * sin(2pi 222 t)
>>> in your calculations and tell me what you get
>>> for 'f'.
>>>
>>> And how do you get 222 Hz out of
>>> cos(2pi 2 t) * sin(2pi 222 t)
>>> Why don't you say it is 2 Hz? What is your
>>> law of physics here? Always pick the bigger
>>> number? Always pick the frequency of the
>>> second term? Always pick the frequency of
>>> the sine?
>>> What is "the frequency" of
>>> cos(2pi 410 t) * cos(2pi 400 t)
>>>
>>>
>>> What is "the frequency" of
>>> cos(2pi 200 t) + cos(2pi 210 t) + cos(2pi 1200 t) + cos(2pi 1207 t)
>>>
>>>
>>>>
>>>>>> So my statements above, in which we have
>>>>>> a relatively slow varying amplitude (4 Hz),
>>>
>>> How do you determine amplitude?
>>> What's the math (or physics) to derive
>>> amplitude?
>>>
>>>>>> are fundamentally spoken valid.
>>>>>> Calling someone an idiot is a weak scientific argument.
>>>>>
>>>>> Yes.
>>>>> And so is "Nonsense." And so is your idea of
>>>>> "the frequency".
>>>>
>>>> Note the piquant difference: nonsense points
>>>> to content and we're not discussing idiots
>>>> (despite a passing by of some very strange
>>>> postings. :)).
>>>>
>>>>>> Hard words break no bones, yet deflate creditability.
>>>
>> Well, I think I've had it. A 'never' ending story.
>> Too much to straighten out. Too much comment
>> needed. Questions moving away from the subject.
>> No more indistinguishable close frequencies.
>> No audible beat, no slow changing envelopes.
>>
>> Take a plot, use a high speed camera or whatever
>> else and see for yourself the particle is vibrating at a
>> period in accordance with 222 Hz. In my view I've
>> sufficiently underpinned the 222 Hz frequency.
>> If you disagree, then do the job. Show your
>> frequencies and elucidate them. (No hint needed,
>> I guess.)
>
> Bravo. Well done. What an impressive
> display of applying the laws of physics.
> Newton, Euler, Gauss, and Fourier have nothing
> on you.

Thanks for your constructive contributions.

gr, Hein

Jim Kelley wrote
> Hein ten Horn wrote:
>
>> That's a misunderstanding.
>> A vibrating element here (such as a cubic micrometre
>> of matter) experiences different changing forces. Yet
>> the element cannot follow all of them at the same time.
>> As a matter of fact the resulting force (the resultant) is
>> fully determining the change of the velocity (vector) of
>> the element.
>
>> The resulting force on our element is changing at the
>> frequency of 222 Hz, so the matter is vibrating at the
>> one and only 222 Hz.
>
> Under the stated conditions there is no sine wave oscillating at 222 Hz.
> The wave has a complex shape and contains spectral components at two
> distinct frequencies (neither of which is 222Hz).

Not a pure sine oscillation (rather than wave), but a near sine
oscillation at an exact period of 1/222 s. The closer the source
frequenties, the better the sine fits a pure sine. Thus if you
wish to get a sufficient near harmonic oscillation, conditions like
"slow changing envelope" are essential.

>>>It might be correct to say that matter is vibrating at an
>>>average, or effective frequency of 222 Hz.
>>
>>
>> No, it is correct. A particle cannot follow two different
>> harmonic oscillations (220 Hz and 224 Hz) at the same
>> time.
>
> The particle also does not average the two frequencies.

Hmm, let's examine this.
From the two composing oscillations you get the overall
displacement:
y(t) = sin(2 pi 220 t) + sin(2 pi 224 t)
From the points of intersection of y(t) at the time-axes you
can find the period of the function, so examine when y(t) = 0.
sin(2 pi 220 t) + sin(2 pi 224 t) = 0
(..)
(Assuming you can do the math.)
(..)
The solutions are:
t = k/(220+224) with k = 0, 1, 2, 3, etc.
so the time between two successive intersections is
Dt = 1/(220+224) s.
With two intersections per period, the period is
twice as large, thus
T = 2/(220+224) s,
hence the frequency is
f = (220+224)/2 = 222 Hz,
which is the arithmetic average of both composing
frequencies.

> The waveform which results from the sum of two pure sine waves is not a pure
> sine wave, and therefore cannot be accurately described at any single
> frequency.

As seen above, the particle oscillates (or vibrates) at 222 Hz.
Since the oscillation is non-harmonic (not a pure sine),
it needs several harmonic oscillations (frequencies,
here 220 Hz and 224 Hz) to compose the oscillation at 222 Hz.

>>>Obviously. It's a very simple matter to verify this by experiment.
>>
>> Indeed, it is. But watch out for misinterpretations of
>> the measuring results! For example, if a spectrum
>> analyzer, being fed with the 222 Hz signal, shows
>> that the signal can be composed from a 220 Hz and
>> a 224 Hz signal, then that won't mean the matter is
>> actually vibrating at those frequencies.
>
> :-) Matter would move in the same way the sound pressure wave does,

To be precise, this is nonsense, but I suspect you're trying
to state somewhat else, and since I'm not able to read your
mind today, I skip that part. :)

> the amplitude of which is easily plotted versus time using Mathematica,
> Mathcad, Sigma Plot, and even Excel. I think you should still give that a
> try.

No peculiarities found.

gr, Hein

Hein ten Horn wrote:

> Hmm, let's examine this.
> From the two composing oscillations you get the overall
> displacement:
> y(t) = sin(2 pi 220 t) + sin(2 pi 224 t)
> From the points of intersection of y(t) at the time-axes you
> can find the period of the function, so examine when y(t) = 0.
> sin(2 pi 220 t) + sin(2 pi 224 t) = 0
> (..)
> (Assuming you can do the math.)
> (..)
> The solutions are:
> t = k/(220+224) with k = 0, 1, 2, 3, etc.
> so the time between two successive intersections is
> Dt = 1/(220+224) s.
> With two intersections per period, the period is
> twice as large, thus
> T = 2/(220+224) s,
> hence the frequency is
> f = (220+224)/2 = 222 Hz,
> which is the arithmetic average of both composing
> frequencies.

As I said before, it might be correct to say that the average, or
effective frequency is 222 Hz. But the actual period varies from
cycle to cycle over a period of 1/(224-220).

>>the amplitude of which is easily plotted versus time using Mathematica,
>>Mathcad, Sigma Plot, and even Excel. I think you should still give that a
>>try.
>
>
> No peculiarities found.

Perhaps you would agree that a change in period of less than 2% might
be difficult to observe - especially when you're not expecting to see
it. To more easily find the 'peculiarities' I suggest that you try
using more widely spaced frequencies.

> gr, Hein

gr right back at ya,

jk

>>>>
>>>> How do you determine amplitude?
>>>> What's the math (or physics) to derive
>>>> amplitude?

The fundamental formular Acos(B) + C is all you need to describe angular
modulation.
Changing the value of A over time determines the amplitude of an AM
modulated carrier.
Changing the value of B over time determines the amplitude of an FM
modulated carrier.
The rate of change of A or B changes the modulation frequency respectively.
C is DC, Y axis offset and has not been discussed here.

r, Bob F.

Hein ten Horn wrote:
>
> Michael A. Terrell wrote:
> > isw wrote:
> >>
> >> That particular receiver doesn't have much of a "front end"; diodes
> >> (with protection) and straight into the first mixer. No RF stage, tuned
> >> or otherwise.
> >
> > It can exceed the PIV of the protection diodes and cause them to
> > short, or explode. That crappy Sony design is where the harmonics came
> > from. The diodes, (or any other semiconductor) with enough RF can
> > generate a lot of spurious signals. It can even come from a rusty joint
> > in the area.
>
> Is the ICF-SW7600GR significantly better performing
> than the ICF-7600D on this?
>
> gr, Hein

I haven't seen the schematics of either model, but most portable SW
recievers suffer from no filtering on the front end, so are susceptible
to overload. A properly designed front end is expensive. Most
manufacturers would rather spend the money on eye candy to make it
attractive to those who don't know what they really need. This is
crossposted to: news:rec.radio.shortwave where the relative merits of
different SW radios are discussed.

I tend to use older, rack mounted equipment that I've restored and
when I have the time, I like to design my own equipment. I only have
one portable receiver, the RS DX-375, which is kept in my hurricane
emergency kit. It was bought on price, alone when it was discontinued
for $50, about eight or nine years ago. The power line and ignition
noise is so high around here that a portable is almost useless. After
the last hurricane, the nearest electricity was over 5 miles away for
about two weeks, and I was picking up stations from all over the world.
It reminded me of visits to my grandparent's farm back in the early
'60s, when their farm was the last one on their road with electricity.
They had nothing that generated noise, other that a few light switches,
when they were flipped on or off. I didn't have a shortwave radio, but
I could pick up AM DX from all over the country, late at night.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Michael A. Terrell wrote:

> I only have > one portable receiver, the RS DX-375, which is kept in
> my hurricane emergency kit. It was bought on price, alone...

I had one and was quite disappointed by its image response (even in
the absence of strong signal IMD, overloading, etc.). For example,
WWV on 10 Mhz was equally strong on 9545 kHz. I never saw the
schematic so I know nothing about its front end and evidently
it is single conversion but one would have hoped for a varactor
tuned preselector ;)

How is image rejection on yours?

Cross-posts limited to sci.electronics.basics and rec.radio.shortwave

Regards,

Michael

msg wrote:
>
> Michael A. Terrell wrote:
>
> > I only have > one portable receiver, the RS DX-375, which is kept in
> > my hurricane emergency kit. It was bought on price, alone...
>
> I had one and was quite disappointed by its image response (even in
> the absence of strong signal IMD, overloading, etc.). For example,
> WWV on 10 Mhz was equally strong on 9545 kHz. I never saw the
> schematic so I know nothing about its front end and evidently
> it is single conversion but one would have hoped for a varactor
> tuned preselector ;)
>
> How is image rejection on yours?


Its acceptable for emergency, but not what I'd want for daily use.
I have a 50 KW FM transmitter and multiple cell sites within a mile
Right now I'm restoring a 1950's era national NC183R with a properly
designed front end, with two tuned RF preamp stages.

http://bama.edebris.com/download/nat...c183/nc183.pdf See page 16
for the front end circuitry. (855 KB (876,468 bytes))


I also have a HP 312B frequency selective voltmeter:

http://bama.edebris.com/download/hp/312bd/hp312bd.pdf (106 MB download).


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Jim Kelley wrote:
> Hein ten Horn wrote:
>
>> Hmm, let's examine this.
>> From the two composing oscillations you get the overall
>> displacement:
>> y(t) = sin(2 pi 220 t) + sin(2 pi 224 t)
>> From the points of intersection of y(t) at the time-axes you
>> can find the period of the function, so examine when y(t) = 0.
>> sin(2 pi 220 t) + sin(2 pi 224 t) = 0
>> (..)
>> (Assuming you can do the math.)
>> (..)
>> The solutions are:
>> t = k/(220+224) with k = 0, 1, 2, 3, etc.
>> so the time between two successive intersections is
>> Dt = 1/(220+224) s.
>> With two intersections per period, the period is
>> twice as large, thus
>> T = 2/(220+224) s,
>> hence the frequency is
>> f = (220+224)/2 = 222 Hz,
>> which is the arithmetic average of both composing
>> frequencies.
>
> As I said before, it might be correct to say that the average, or effective
> frequency is 222 Hz. But the actual period varies from cycle to cycle over
> a period of 1/(224-220).
>
>>> the amplitude of which is easily plotted versus time using Mathematica,
>>> Mathcad, Sigma Plot, and even Excel. I think you should still give that a
>>> try.
>>
>>
>> No peculiarities found.
>
> Perhaps you would agree that a change in period of less than 2% might be
> difficult to observe - especially when you're not expecting to see it. To
> more easily find the 'peculiarities' I suggest that you try using more
> widely spaced frequencies.

Before we go any further I'd like to exclude
that we are talking at cross-purposes.
Are you pointing at the irregularities which
can occur when the envelope passes zero?
(That phenomenon has already been
mentioned in this thread.)

>
> gr right back at ya,

:-)
"gr" is not customary, but, when writing it satisfies
in several languages: German (gruß, grüße),
Dutch (groet, groeten) and English.

Adieu, Hein