>I don't want to poo-poo parasitics, but there are some fundamental
>engineering points that you should be sure of before coming to that
>conclusion:
And they are good points indeed!
>
>Be careful about overloading the spectrum analyzer. Most of them will
>immediately produce all sorts of spurs on the display if driven above 0dBM
>or whatever the peak limit of the instrument is. It only takes one carrier
>or harmonic to do this, and make a real mess on the screen.
Yes, yes, yes...Absolutely! Back in my days of designing 16 tone linear
amps, guys would make that mistake all the time (including me). It's
amazing what adding some attenuation to the front end of a spectrum
analyzer will do. Remember these things are capable of reading sinals
that are less than -100 dBm, so they are REALLY sensitive instruments.
>Were these "signals to 350 MHZ" harmonically related? or were they
>intermod? or parasites? A look at their individual frequencies would help
>detemine which. Harmonics would be a different thing entirely, as far as
>treatment goes.
Yup...good point.
>
>Finally, keying or pulsing an RF signal creates a broadband spectrum of
>(sinx/x like?) sidebands around the fundamental and the harmonics. It is
>one of the problems with pulsed RF systems, trying to determine what a
>carrier looks like (stability, parasites) with a spectrum analyzer. We see
>it all the time with our RF plant. I don't know the rep rate or duty factor
>of your keyer, but something to keep in mind. Maybe others who use fast
>pulsers care to comment. The experience I am talking about is with 60-100
>Hz rep rates and millisecond pulses or less. What is the spectrum like from
>these electronic pulsers that hams use?
I must say, correct again...This poses an interesting question:
When you use a pulser to tune your amp, is it possible that you are
actually creating MORE splatter and hash due to the sinx/x (technical
name is the "sinc" function) sidebands?
73,
Jon
KE9NA
-------------------------------------
Jon Ogden
KE9NA
http://www.qsl.net/ke9na
"A life lived in fear is a life half lived."
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