Hi Hideho san,

>> I use a low pass filter which ensures that the harmonics are -50 dBc or
>> lower. I think the tuned antenna also helps with not radiating too much
> My quick calculation resulted in -120dBc necessary, to reduce QRM to adjacent 
> houses,
>  (I may be wrong)., and I am thinking how to make it.

In Australia, for frequencies below 30 MHz we need to reduce our
harmonics by the lesser of:
1) 43 db + 10*log(PEP)
2) 50 dB

where PEP is peak power to the antenna. When I was allocated an
experimental license for 500 kHz, I was asked to demonstrate that my
harmonics are reduced by 60 dB (from memory).

73, Dimitris Vk1SV