[Amps] CB Amps or full spectrum???

[Steve Katz]

>I wondering about your comment about filtering.  If you look at the tank
circuit of these amps, you see a pi network that is usually no different
than any other amp, except the coil is small turns wise because it is for 11
meters (and close to 10 meters as well).   So what kind of "filtering" are
you talking about?
If the pi network is not different than, say, a 30L-1 or an SB 200 or any
other amp with a pi network, why would harmonics be any more of a problem
than with other amps?
Ray  wa7itz<

::Lots of reasons.  30L-1s and SB200s were designed to operate in a linear
mode, Class AB2, and accommodate medium power exciters in the 100W PEP range
to produce their rated output power.  They use tubes, power supplies and
other components rated for the intended service and power.  The "CB" amps
referenced don't.  The solid state ones contain a "driver" stage intended
for about 4W PEP drive power and maybe somewhat linear up to about 20W PEP
output; then that output is used to typically *over*drive the final power
amplifying stage, resulting in lots of harmonic distortion, much more than a
30L-1 with negative feedback could ever create even if it were overdriven.
Classic tuned circuitry won't be enough to suppress those harmonics down to
lawful levels.  An even bigger problem is that the overdriven stages, not
properly biased and using cheaper components (like 12V bipolars instead of
50V FETs as used in the "amateur" higher powered amplifiers) create tons of
IMD products which are very close to carrier frequency and cannot be
"filtered out" by any kind of filter -- they're harmonics of the modulating
frequency, not the carrier frequency, so they're within just several kHz of
carrier.  -WB2WIK/6