Hi!

I am planning to increase my RF output considerably beyond the QRP
levels I have been using thus far. The idea is to construct a 100 W
PA-module with IRF510-fets
as many others have done before... At this stage I will concentrate in
the 160, 80 and maybe 40 m because the switching fets may not work too
well at higher frequencies and also I feel that this extra power is most
urgently needed in the lowest bands.

For this power level two pairs of IRF510 are needed in push-pull
configuration and with Vdd = 30 V. The question that has bothered me is
the type of output matching.In order to reach the 100W level an
impedance step-up 1:4 is necessary. After studying ARRL HB:s from the
past decades, RSGB material and Solid State Desing for Radio Amateurs I
have noticed that a conventional broadband transformer with two rows of
ferrite toroids is used almost invariably. In some cases like the 300W
design by the late H. Granberg (from Motorola) a transmission line
transformer wound on two separate toroids is used. What is missing
totally (in this power level, at least) is the application of large
single toroids as transformers (why ???).

Another possibility which might be feasible is a narrowband (T-)
matching section for each band (max 3) followed by the standard low pass
filter.

Any comments/suggestions from more experienced homebrewers ? Also, if a
better but still low cost alternative for IFR510 has appeared in the
market, this info also taken into consideration when finalizing the
design...

73 de Heikki (OH2LZI)