"Earl Kiosterud" <someone@[EMAIL PROTECTED]
> wrote in message
news:KDmWj.52$vE.31@[EMAIL PROTECTED]
>
> "Randy Yates" <yates@[EMAIL PROTECTED]
> wrote in message
news:m3hcd2p3cc.fsf@[EMAIL PROTECTED]
>> "Earl Kiosterud" <someone@[EMAIL PROTECTED]
> writes:
>>
>>> "Randy Yates" <yates@[EMAIL PROTECTED]
> wrote in message
news:m31w46svgx.fsf@[EMAIL PROTECTED]
>>>> "Chronic Philharmonic" <karl.uppiano@[EMAIL PROTECTED]
> writes:
>>>>
>>>>> "Randy Yates" <yates@[EMAIL PROTECTED]
> wrote in message
>>>>> news:m3k5hzj58s.fsf@[EMAIL PROTECTED]
>>>>>> "Green Xenon [Radium]" <glucegen1@[EMAIL PROTECTED]
> writes:
>>>>>>
>>>>>>> Hi:
>>>>>>>
>>>>>>> Is it true that purely-analog audio devices [such as analog
cassette,
>>>>>>> AM radio, and the pre-digital telephone systems*] are immune to
>>>>>>> aliasing?
>>>>>>
>>>>>> Yes.
>>>>>
>>>>> Well... AM radio is not immune to aliasing, although we rarely
encounter it
>>>>> in practice
>>>>
>>>> How would AM ever alias?
>>>> --
>>>> % Randy Yates % "Midnight, on the water...
>>>> %% Fuquay-Varina, NC % I saw... the ocean's daughter."
>>>> %%% 919-577-9882 % 'Can't Get It Out Of My Head'
>>>> %%%% <yates@[EMAIL PROTECTED]
> % *El Dorado*, Electric Light
Orchestra
>>>> http://www.digitalsignallabs.com
>>>
>>> An AM radio station operating at 1 MHz would have to have the baseband
limited to 500
>>> KHz,
>>> or aliases would appear. For example a 600 KHz baseband component
would appear at 400
>>> KHz.
>>> This obviously ain't gonna happen in any real world situation, but
imagine an AM station
>>> operating at 10 KHz. It would have to keep the audio limited to below
it's Nyquist
>>> frequency of 5 Khz.
>>>
>>> I'm using the term Nyquist frequency somewhat incorrectly, as it
technically applies to
>>> sampled systems. But it still works, and we know what we mean! :)
>>
>> Hi Earl,
>>
>> I see what you mean now. I'd say that comes as close to an "analog
>> alias" as you'll get. It is mathematically almost the same thing. (I
say
>> almost since the analog system involves only two Dirac delta functions
>> while a digital one involves an infinite number.)
>>
>> But I really don't think this is what was in Radium's mind when he
>> asked.
>> --
>> % Randy Yates % "...the answer lies within your soul
>> %% Fuquay-Varina, NC % 'cause no one knows which side
>> %%% 919-577-9882 % the coin will
fall."
>> %%%% <yates@[EMAIL PROTECTED]
> % 'Big Wheels', *Out of the Blue*, ELO
>> http://www.digitalsignallabs.com
>
> Hi Randy,
>
> Oops. I spoke too soon. It occurred to me while I was working in the
yard. A 10KHz AM
> station could modulate to 10 KHz. As Don pointed out in another thread,
there's no
> baseband in the modulator output, so there's no concern about the
difference component
> (sideband) overlapping with it, as there is with sampling. But if you
try to modulate
> above 10K, the difference product ends up negative, and folds into the
band. 12KHz
> modulation would produce a component at 2 KHz. I don't know of a
demodulator that could
> properly sort that out. I've always considered that an alias, but it's
not the same as in
> a sampling system, such as when the difference component creeps downward
past Nyquist as
> the baseband creeps upwards past it.
>
> I realize I've probably been misusing the term "alias." When in Rome.
:)
> --
> Earl
>
Hey Randy,
Oops again. I said that I didn't know of a demodulator that could sort
out the 2 KHz
component that was the result of 12K audio. A plain old envelope (diode)
detector would be
confounded, and the transmitter would have to be constrained to 10K audio.
But my
favorite, the AM synchronous demodulator, could easily do that, since it
could be set up to
use only the upper set of sidebands. In that case the transmitter could
modulate up to 20K,
above which point the difference-frequency sidebands would creep into our
upper set of
sidebands and muck up the works.
I don't know what Radium's intentions are, but he sometimes sparks
discussions that get us
thinking and we end up sorting things out.
Regards from Virginia Beach,
--
Earl
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