[hpsdr] PennyWhistle MOSFET's

[Helmut Oeller]

Hi Riho,

sorry, I can't redesign your amp by email remotely :). May be the
following remarks are helpful for you yet:

1. Acc. to the datasheet the 1 dB compression point of a RD70HVF1 is
approx. at 45W, i.e. a push-pull  configuration should be able to
deliver up to 90W linear power.

2. the load for each Mosfet can be calculated with R = (Ub^2)/2P. You'll
get approx. something around 5.4 ohms for the two Mosfets together @ Ub
= 15V.

3. A well-performing 1:9 transmission line transformer should substitute
that simple conventional trafo for matching the 5.4 ohms to 50 ohms.
Moreover the DC feed for the Mosfets should be done with a bifilar
choke. This improves  IMD too.

4. These Mosfets are specified for a quiescent current of 2 A, i.e. 30W
(!) dissipation for each Mosfet. A well-designed  bias stabilisation is
strongly recommended to avoid thermal runaway effects and migration,
which causes additional nonlinear distortion.

73, Helmut, DC6NY