Tom and Rich,
This whole discussion makes no sense to me. If I put two sinewaves into any
kind of
nonlinear network, I would expect to see IMD products as well as harmonics
results.
After passing thru the non-linearity, the two sine waves will no longer be
linearly
independent - in essence the two signals should begin to cross modulate each
other.
Please elaborate - thanks!
73 de Mike, W4EF........................
-----Original Message-----
From: Tom Rauch [SMTP:w8ji@contesting.com]
Sent: Saturday, May 29, 1999 3:49 AM
To: 'AMPS'; Gilmer, Mike
Subject: RE: [AMPS] Re: Ferrite Rod for 6M Amp
Hi Mike,
> > >People who aren't totally familiar with PA operation sometimes
> > >confuse harmonic distortion with the type of distortion that causes
> > >splatter. Splatter is NOT caused by harmonic distortion, splatter is
> > >caused by amplitude non-linearity in the envelope shape.
>
> Is not amplitude non-linearity in the envelope of the RF actually
> (usually?) harmonic distortion in the AUDIO? This is splatter, right?
> Perhaps two-tone type stuff in the not-so-linear (on purpose or otherwise)
> parts of the transmitter can contribute, too, but the audio is where we
> tend to create splatter.
Absolutely not!! That's a common misconception, but totally untrue.
Call the distortion by the proper name, and you will see why it is
true. Harmonic distortion, the RF distortion that occurs at a
fractional RF-cycle rate, only produces even-order products of the
original signal(s). If I had a transmitter on 7.0 MHz, the closest
harmonic distortion product would be on 14 MHz. That would be
true even if it was multi-tone modulation.
If the same transmitter was modulated by a two-tone signal, but
had envelope amplitude non-linearity, it could produce what we call
"splatter" or IMD products.
Now, I don't believe for a second Rich measured what he "claims"
to have measured because the cores he claims are "no good" are
used in hundreds or thousands of broad band applications where
harmonic distortion would be absolutely intolerable (multi-band
CATV applications and other broadband amplifiers, harmonic
suppression, etc) but even if he did measure fraction RF-cycle
distortion it wouldn't mean a thing for filtered RF amplifiers. The
output filters would remove virtually every trace of harmonic
distortion.
If that wasn't true, we couldn't use class AB or B single ended PA's
in amplifiers...and push-pull RF amps would be cleaner for IMD
than single ended amps....and that certainly is not true.
> > >> ? Harmonic distortion has everything to do with sine waveshape
> > >> distortion.
> > >
> > >That's right. But harmonic distortion has no ill effects in a narrow
> > >band PA.
> > >
> > It does when your neighbors are watching the NBA playoffs.
> >
>
> Harmonics content in the RF are not and do not cause "splatter".
>
> However, harmonics of the RF do make it out the connector (albeit
> 30-40dB down) and into the antenna and get radiated, even though the PA
> and the antenna are "narrow-band".
What a poor PA you have! It doesn't even pass FCC requirements
beyond a hundred watts or so output! Not only that, the tube
generates harmonics that are much worse than any other
components, and you seem to follow (swallow?) the argument that
a filament choke carrying a ting bit of magnetization from drive
power would be a problem in a system where the tube itself only
conducts for a fraction of a cycle?
73, Tom W8JI
w8ji@contesting.com
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