Interesting comments on harmonic suppression. There are a lot of variables,
especially regarding the parasitic reactances, which as Tom says, substantially
modify the result. My experience for what it's worth, is that on the LF bands
where the parasitics at the harmonic frequencies are less unknown and variable,
the harmonic level follows the theory pretty well - even at 30kW. At that sort
of power, the physical size of components makes the parasitic reactances even
more of a problem. But on the higher bands, the pi-L, depending on
implementation.may give you no advantage, and a pi may meet the requirements,
despite it, through the use of over simplifications, theoretically failing to
do so.
A difficulty exists in that the Radio Regulations require, as far as
transmitters under 30MHz are concerned, a higher level of attenuation than
either the European EMC Standard for commercially available amateur radio
equipment, or the limits in FCC Part 97. The Radio Regs limits (and the
European ERC REC74-01) require harmonics for transmitters operating under 30MHz
to be 43 + 10 log P, with no requirement to exceed 50dB. Incidentally, the regs
are unclear whether the harmonic levels above 30MHz for a transmitter operating
below 30MHz are the HF levels or the more restrictive VHF rules (-43 +10 log
P, without a requirement to be more than 70dB). The reasons for these anomalies
are only a degree of bureaucratic ineptitude......somewhat sad, since both teh
guys concerned at the FCC were hams (although in different departments), and
they didn't communicate. But it means, at least as far as the UK is concerned,
that the licence requires the licencee to abide by the relevant In
ternational Telecommunication Conventions, but the equipment that he (or she)
can buy may not meet those, as does the official limit for the equipment in the
UK, and yet is totally legal to sell!!!
73
Peter G3RZP
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