Reply by radi...@aol.com●December 21, 20062006-12-21
On Dec 20, 7:40=A0pm, Jerry Avins <j...@ieee.org> wrote:
> radio...@aol.com wrote:
> > Jerry Avins wrote:
> >> radio...@aol.com wrote:
>
> >> =A0 =A0...
>
> >>> =A0 =A0 =A0 =A0 It's a good thing most all speakers are directional (=
and
> >>> antennas) to
> >>> a large degree, so we don't waste sending energy where no one will he=
ar
> >>> or receive it.
> >> The design of some specific radiation patterns would be simplified if =
we
> >> had isotropic radiators available as array elements.
>
> > =A0 =A0 =A0 =A0 =A0An ideal isotropic radiator would not be very useful,
> > as you would waste ERP into the sky and the ground, where
> > there aren't any receivers.
>
> > =A0 =A0 =A0 =A0 That's why the "doughnut" shape of a 1/4 wave, 5/8ths, =
or
> > dipole is much better suited (especially the low angle of radiation
> > of the 5/8ths).Once a directional array is constructed by any means, no=
power is wasted
> in a direction that the array doesn't illuminate.
>
> The design of directional radiators proceeds by combining elements with
> broad patterns into directional arrays by selecting spacing, resonant
> frequency, and phasing. For certain purposes, isotropic radiators are
> the simplest to work with. Vertical elements are isotropic in the
> horizontal plane and are often the basis for high-gain narrow-band
> arrays. Broadside and end-fire arrays are elementary examples.
>
I've never heard of someone describing verticals
as "isotropic in the horizontal plane", but yeah, they certainly
are. Phased-arrays (4 vertical antennas) are the basis for
direction finding set ups, so can be used for transmit and
receive due to reciprocity.
S
Reply by Jerry Avins●December 20, 20062006-12-20
radio913@aol.com wrote:
> Jerry Avins wrote:
>> radio913@aol.com wrote:
>>
>> ...
>>
>>> It's a good thing most all speakers are directional (and
>>> antennas) to
>>> a large degree, so we don't waste sending energy where no one will hear
>>> or receive it.
>> The design of some specific radiation patterns would be simplified if we
>> had isotropic radiators available as array elements.
>>
>
> An ideal isotropic radiator would not be very useful,
> as you would waste ERP into the sky and the ground, where
> there aren't any receivers.
>
> That's why the "doughnut" shape of a 1/4 wave, 5/8ths, or
> dipole is much better suited (especially the low angle of radiation
> of the 5/8ths).
Once a directional array is constructed by any means, no power is wasted
in a direction that the array doesn't illuminate.
The design of directional radiators proceeds by combining elements with
broad patterns into directional arrays by selecting spacing, resonant
frequency, and phasing. For certain purposes, isotropic radiators are
the simplest to work with. Vertical elements are isotropic in the
horizontal plane and are often the basis for high-gain narrow-band
arrays. Broadside and end-fire arrays are elementary examples.
Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by radi...@aol.com●December 20, 20062006-12-20
Jerry Avins wrote:
> radio913@aol.com wrote:
>
> ...
>
> > It's a good thing most all speakers are directional (and
> > antennas) to
> > a large degree, so we don't waste sending energy where no one will hear
> > or receive it.
>
> The design of some specific radiation patterns would be simplified if we
> had isotropic radiators available as array elements.
>
An ideal isotropic radiator would not be very useful,
as you would waste ERP into the sky and the ground, where
there aren't any receivers.
That's why the "doughnut" shape of a 1/4 wave, 5/8ths, or
dipole is much better suited (especially the low angle of radiation
of the 5/8ths).
S
Reply by Jerry Avins●December 20, 20062006-12-20
radio913@aol.com wrote:
...
> It's a good thing most all speakers are directional (and
> antennas) to
> a large degree, so we don't waste sending energy where no one will hear
> or receive it.
The design of some specific radiation patterns would be simplified if we
had isotropic radiators available as array elements.
Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by radi...@aol.com●December 20, 20062006-12-20
On Dec 19, 7:06=A0pm, Jerry Avins <j...@ieee.org> wrote:
> radio...@aol.com wrote:
> > Jerry Avins wrote:
> >> radio...@aol.com wrote:
> >>> On Dec 18, 8:21?pm, "Clay" <phys...@bellsouth.net> wrote:
> >>>> radio...@aol.com wrote:
>
> >>>>> In reality, we don't have isotropic radiators, as any antenna has
> >>>>> some directivity. ?However, it's useful to compare any antenna to
> >>>>> the isotropic case, using dBi (decibels over isotropic), as we then
> >>>>> have a standard.
> >>>>> ? ? ?The same would apply to the world of sound or noise:Well certa=
inly for E-M, the minimum order (in terms of a multipole
> >>>> expansion) for a radiator is a dipole. However, for sound (which is
> >>>> longitudinal instead of transverse) can be created by a monopole
> >>>> source. Hence a true isotropic radiator for sound can exist.
>
> >>> =A0 =A0 =A0 =A0Where have you seen/heard a true isotropic radiator fo=
r sound?
> >> In the laboratory. Imagine a liquid-filled balloon in which the intern=
al
> >> volume is forced to change according to a schedule that moves the
> >> surface sinusoidally. Being a radially symmetric structure, it is of
> >> course isotropic. The device served to show that a spherical cluster of
> >> dynamic loudspeakers surrounded by a diffuser (felt) behaved
> >> substantially the same way.
>
> > =A0 =A0 =A0 =A0 How did you suspend the balloon? =A0Or was it mounted on
> > a pole or shaft of some sort? =A0It would be difficult if not impossible
> > to have a truly isotropic sound radiator.The balloon was suspended from=
the tube that moved the fluid. It's
> diameter was a very small fraction of a wavelength of the test
> frequency, so both reflection and diffraction were negligible.
>
> > =A0 =A0 =A0 =A0 You could consider a suspended firecracker as being
> > roughly isotropic, as it radiates sound in all directions roughly
> > equally.Provided the thread it hung from is thin enough, which is proba=
ble.
>
> >>> =A0 =A0 =A0 =A0Every source of sound i have heard was obviously direc=
tional.
> >> Limited experience? How about eight folded horns -- two stacked cluste=
rs
> >> of four =A0back to back -- hanging in space? A bit directional, perhap=
s,
> >> but not obviously so.
>
> > =A0 =A0 =A0 =A0 =A0 It would be far from a true isotropic sound source,
> > especially
> > in the near field, but the further away, it would approximate it.
>
> > =A0 =A0 =A0 =A0 =A0 But why would you ever need an isotropic speaker of
> > any sort? =A0Unless you were in a spinning sphere, outside the
> > pull of gravity, and your audience was covering the whole inner
> > surface. =A0And even then, you would lose any stereo imaging.Why does s=
tereo get lost? As to why one is wanted; a reference of some sort?
>
In the RF world, you would simply use the power fed to the idea
isotropic to calculate Watts per Steradian, so we don't really need an
actual isotropic radiator. Ditto for the acoustic world.
It's a good thing most all speakers are directional (and
antennas) to
a large degree, so we don't waste sending energy where no one will hear
or receive it.
S
Reply by Jerry Avins●December 19, 20062006-12-19
radio913@aol.com wrote:
> Jerry Avins wrote:
>> radio913@aol.com wrote:
>>> On Dec 18, 8:21?pm, "Clay" <phys...@bellsouth.net> wrote:
>>>> radio...@aol.com wrote:
>>>>
>>>>> In reality, we don't have isotropic radiators, as any antenna has
>>>>> some directivity. ?However, it's useful to compare any antenna to
>>>>> the isotropic case, using dBi (decibels over isotropic), as we then
>>>>> have a standard.
>>>>> ? ? ?The same would apply to the world of sound or noise:Well certainly for E-M, the minimum order (in terms of a multipole
>>>> expansion) for a radiator is a dipole. However, for sound (which is
>>>> longitudinal instead of transverse) can be created by a monopole
>>>> source. Hence a true isotropic radiator for sound can exist.
>>>>
>>> Where have you seen/heard a true isotropic radiator for sound?
>> In the laboratory. Imagine a liquid-filled balloon in which the internal
>> volume is forced to change according to a schedule that moves the
>> surface sinusoidally. Being a radially symmetric structure, it is of
>> course isotropic. The device served to show that a spherical cluster of
>> dynamic loudspeakers surrounded by a diffuser (felt) behaved
>> substantially the same way.
>
> How did you suspend the balloon? Or was it mounted on
> a pole or shaft of some sort? It would be difficult if not impossible
> to have a truly isotropic sound radiator.
The balloon was suspended from the tube that moved the fluid. It's
diameter was a very small fraction of a wavelength of the test
frequency, so both reflection and diffraction were negligible.
> You could consider a suspended firecracker as being
> roughly isotropic, as it radiates sound in all directions roughly
> equally.
Provided the thread it hung from is thin enough, which is probable.
>>> Every source of sound i have heard was obviously directional.
>> Limited experience? How about eight folded horns -- two stacked clusters
>> of four back to back -- hanging in space? A bit directional, perhaps,
>> but not obviously so.
>
> It would be far from a true isotropic sound source,
> especially
> in the near field, but the further away, it would approximate it.
>
> But why would you ever need an isotropic speaker of
> any sort? Unless you were in a spinning sphere, outside the
> pull of gravity, and your audience was covering the whole inner
> surface. And even then, you would lose any stereo imaging.
Why does stereo get lost? As to why one is wanted; a reference of some sort?
...
Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by radi...@aol.com●December 19, 20062006-12-19
Jerry Avins wrote:
> radio913@aol.com wrote:
> >
> > On Dec 18, 8:21?pm, "Clay" <phys...@bellsouth.net> wrote:
> >> radio...@aol.com wrote:
> >>
> >>> In reality, we don't have isotropic radiators, as any antenna has
> >>> some directivity. ?However, it's useful to compare any antenna to
> >>> the isotropic case, using dBi (decibels over isotropic), as we then
> >>> have a standard.
> >>> ? ? ?The same would apply to the world of sound or noise:Well certain=
ly for E-M, the minimum order (in terms of a multipole
> >> expansion) for a radiator is a dipole. However, for sound (which is
> >> longitudinal instead of transverse) can be created by a monopole
> >> source. Hence a true isotropic radiator for sound can exist.
> >>
> >
> > Where have you seen/heard a true isotropic radiator for sound?
>
> In the laboratory. Imagine a liquid-filled balloon in which the internal
> volume is forced to change according to a schedule that moves the
> surface sinusoidally. Being a radially symmetric structure, it is of
> course isotropic. The device served to show that a spherical cluster of
> dynamic loudspeakers surrounded by a diffuser (felt) behaved
> substantially the same way.
How did you suspend the balloon? Or was it mounted on
a pole or shaft of some sort? It would be difficult if not impossible
to have a truly isotropic sound radiator.
You could consider a suspended firecracker as being
roughly isotropic, as it radiates sound in all directions roughly
equally.
>
> > Every source of sound i have heard was obviously directional.
>
> Limited experience? How about eight folded horns -- two stacked clusters
> of four back to back -- hanging in space? A bit directional, perhaps,
> but not obviously so.
It would be far from a true isotropic sound source,
especially
in the near field, but the further away, it would approximate it.
But why would you ever need an isotropic speaker of
any sort? Unless you were in a spinning sphere, outside the
pull of gravity, and your audience was covering the whole inner
surface. And even then, you would lose any stereo imaging.
>
> > The fact that you cannot build one doesn't diminish the
> > usefulness of the mathematical concept as a reference to compare to.
>
> Indeed!
>
> Jerry
> --
> Engineering is the art of making what you want from things you can get.
> =AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=
>
> On Dec 18, 8:21�pm, "Clay" <phys...@bellsouth.net> wrote:
>> radio...@aol.com wrote:
>>
>>> In reality, we don't have isotropic radiators, as any antenna has
>>> some directivity. �However, it's useful to compare any antenna to
>>> the isotropic case, using dBi (decibels over isotropic), as we then
>>> have a standard.
>>> � � �The same would apply to the world of sound or noise:Well certainly for E-M, the minimum order (in terms of a multipole
>> expansion) for a radiator is a dipole. However, for sound (which is
>> longitudinal instead of transverse) can be created by a monopole
>> source. Hence a true isotropic radiator for sound can exist.
>>
>
> Where have you seen/heard a true isotropic radiator for sound?
In the laboratory. Imagine a liquid-filled balloon in which the internal
volume is forced to change according to a schedule that moves the
surface sinusoidally. Being a radially symmetric structure, it is of
course isotropic. The device served to show that a spherical cluster of
dynamic loudspeakers surrounded by a diffuser (felt) behaved
substantially the same way.
> Every source of sound i have heard was obviously directional.
Limited experience? How about eight folded horns -- two stacked clusters
of four back to back -- hanging in space? A bit directional, perhaps,
but not obviously so.
> The fact that you cannot build one doesn't diminish the
> usefulness of the mathematical concept as a reference to compare to.
Indeed!
Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by radi...@aol.com●December 19, 20062006-12-19
On Dec 18, 8:21=A0pm, "Clay" <phys...@bellsouth.net> wrote:
> radio...@aol.com wrote:
>
> > In reality, we don't have isotropic radiators, as any antenna has
> > some directivity. =A0However, it's useful to compare any antenna to
> > the isotropic case, using dBi (decibels over isotropic), as we then
> > have a standard.
>
> > =A0 =A0 =A0The same would apply to the world of sound or noise:Well cer=
tainly for E-M, the minimum order (in terms of a multipole
> expansion) for a radiator is a dipole. However, for sound (which is
> longitudinal instead of transverse) can be created by a monopole
> source. Hence a true isotropic radiator for sound can exist.
>
Where have you seen/heard a true isotropic radiator for sound?
Every source of sound i have heard was obviously directional.
The fact that you cannot build one doesn't diminish the
usefulness
of the mathematical concept as a reference to compare to.
S
Reply by Clay●December 19, 20062006-12-19
radio913@aol.com wrote:
>>
> In reality, we don't have isotropic radiators, as any antenna has
> some directivity. However, it's useful to compare any antenna to
> the isotropic case, using dBi (decibels over isotropic), as we then
> have a standard.
>
> The same would apply to the world of sound or noise:
>
Well certainly for E-M, the minimum order (in terms of a multipole
expansion) for a radiator is a dipole. However, for sound (which is
longitudinal instead of transverse) can be created by a monopole
source. Hence a true isotropic radiator for sound can exist.
Clay