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Re: [Amps] Pi-L Network

Subject: Re: [Amps] Pi-L Network
From: Peter Chadwick <>
Date: Wed, 28 Mar 2007 20:38:11 +0200 (CEST)
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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!!!
Peter G3RZP
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