Noisy DSP radios theory

[N8CEP]

I believe it is a fault of all DSP radios that they amplify the HARMONICS of a sound too much. In our earlier days before DSP,
radio amplifiers tended to amplify only the fundamental of a sound and not the partials (harmonics 2,3,4,5,6 etc.) Forgive me if this
doesn't seem clear. I am piano tuner and deal with sound and harmonics all day. But if the sound and ALL of its nearby
harmonics are all amplified equally, or the harmonics are not down in amplitude far enough from the fundamental, you might get a busy,
or noisy receiver. This could equate to amplifying the harmonics too much in a final PA and having a 'noisy" or as we call
it, a dirty transmitter.

Now I admit I have no equipment with which to test my theory but I think some smart people like Rob Sherwood who deals with
receivers all the time might be able to test this theory.

Well thanks for listening and enjoy those great Elecraft radios!

73 Keith W8GX

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[Alan Bloom]

On Thu, 2010-01-07 at 12:24 -0500, Keith Hamilton wrote:
> I believe it is a fault of all DSP radios that they amplify the
> HARMONICS of a sound too much. ... I am piano tuner and deal with
> sound and harmonics all day. But if the sound and ALL of its nearby
> harmonics are all amplified equally, or the harmonics are not down
> in amplitude far enough from the fundamental, you might get a busy,
> or noisy receiver. ...

I remember the first time I went to a live classical music concert years
ago.  I thought the music sounded "tinny".  At that time I was
accustomed to listening to music on AM radio using an old tube-type
console set with a big boomy speaker.

It's all what you are used to.  If you switch from a receiver with lots
of high-frequency rolloff to one with a flat response, it will sound too
harsh until you get used to it.

Al N1AL


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[K1LI]

Keith,

I wonder why you believe that "all DSPs" would "amplify harmonics." When
properly designed, a DSP behaves in a linear fashion - i.e., it does not
produce the harmonic distortion you describe. The criteria for "proper DSP
design" include limiting the bandwidth of the input signal to prevent
aliasing (the Nyquist criterion), limiting the amplitude of the signal to
avoid saturating the A/D converter and scaling the DSP operations to avoid
numerical overflows.

I agree with your assertion that harmonic distortion could produce a "noisy
sounding" receiver, but I can't think of any reason why well-designed
"radios... before DSP" necessarily had any more or less tendency to behave
in a linear fashion; being square-law devices, tube-type and MOSFET-based
amplifiers produce more even-order harmonic distortion which some judge as
less objectionable (purportedly because "mechanical" sound generators, like
musical instruments, produce even-order harmonics) than bipolar-junction
transistors.

--
73 -- Brian -- K1LI

On Thu, Jan 7, 2010 at 12:24 PM, Keith Hamilton <[hidden email]>wrote:

> I believe it is a fault of all DSP radios that they amplify the HARMONICS
> of a sound too much. In our earlier days before DSP, radio amplifiers tended
> to amplify only the fundamental of a sound and not the partials (harmonics
> 2,3,4,5,6 etc.) ... But if the sound and ALL of its nearby harmonics are all
> amplified equally, or the harmonics are not down in amplitude far enough
> from the fundamental, you might get a busy, or noisy receiver. This could
> equate to amplifying the harmonics too much in a final PA and having a
> 'noisy" or as we call it, a dirty transmitter.
>
>

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