You may well have problems meeting FCC harmonic requirements with just a pi.
You certainly will not meet European requirements, or the ITU Recommendation
SM.329-7 on spurious emissions with just a pi. In fact, even a pi-L is a bit
marginal. (50dB down on harmonics below 30MHz)
As far as the transformer goes, winding it with 93 ohm coax and using it as
transmission line transformer puts minimal flux density in the core, thus
minimising problems there. 100 ohm coax would be theoretically better, but
93 ohms is available, and some of it is fairly hefty. Even RG58 is rated for
1 kW up to 10MHz, and the 93 ohm silver plated conductor, Teflon insulated
stuff is rated a bit higher - the resistive loss is less, because the
current is lower.
73
Peter G3RZP
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