>If a high order 10M harmonic is only 30dB down (older design amps) at the
>analyzer then do some mental gymnastics and figure where the other KW or
>so is being absorbed. If you happen to say the tune cap/bandswitch/ tank
>coil, you may just have won a prize. By the time the "bad RF" gets to the
>loading cap it has already done its damage. Just look at the tank coil as
>similar to a plate choke with a mess of series and parallel resonances
>caused by the switch, coupled C and L and even the shape/size of the
>enclosure.
>
>With modern FCC spec amps tell me where that 50+ dB is going Rich?
>Wouldnt you begin to suspect that the better the harmonic attenuation in
>the tank circuit the more stress on the components? Would that not
>partially explain the propensity of some of our newer amps to have major
>pyrotechnics in the switch and tune cap?
Based on my knowledge of filter designs (I sell high power filters), the
filter does not "abosrb" energy outside of it's passband. Rather it
rejects it. If you do a network analyzer plot of a filter, the input SWR
outside of the passband will be very HIGH. Inside the passband, it's
very LOW. In an ideal filter, there are no resistive components (i.e. no
energy dissipation). So the concept that a filter absorbs the out of
band energy, just does not wash. In the real world, yes there are some
resistive components in the filter. But still if the reflection
coefficient of the filter is large a particular frequency, the majority
of that energy will mainly be reflected and won't even get into the
filter.
Why am I talking about filters? Because the pi-network in an amp IS a
filter as well as a matching network.
So where does the *bad* RF go? It is reflected by the pi-net and stays
effectively in that portion of the circuit between the anode of the tube
and the Tune C.
Filters do NOT absorb the out of band energy. They reflect it.
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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