"Jim" wrote in message
...
Most power MosFets have a large Gate to Source capacitance which makes
it
difficult to use them at radio frequencies.

It can be done, but the higher the desired operating frequency the
greater effect the parasitic capacitance has, so most designs I have seen
were up to 7 MHz and that was about the upper limit.

A German ham radio magazine just published a project for a 400W MOSFET PA
covering the 80...20m bands:
http://www.vth.de/FUNK/funk/09_05/28.asp

Markus HB9BRJ

On Wed, 14 Sep 2005 09:14:26 +0200, "Markus L"
wrote:

"Jim" wrote in message
...
Most power MosFets have a large Gate to Source capacitance which makes
it
difficult to use them at radio frequencies.

It can be done, but the higher the desired operating frequency the
greater effect the parasitic capacitance has, so most designs I have seen
were up to 7 MHz and that was about the upper limit.

A German ham radio magazine just published a project for a 400W MOSFET PA
covering the 80...20m bands:
http://www.vth.de/FUNK/funk/09_05/28.asp

Markus HB9BRJ


Yes but were they class E or linear? There are a number of AM ops on
160/75/40m running 1kw AM phone using class E FET. However class E
for 6M I havent seen yet. The german design would not run at 6m and
thats what the initial posting asked for.

Those power fets at lower frequencies are a very useful devices but at
VHF their characteristics are difficult to accomodate.

Allison

On Tue, 13 Sep 2005 20:33:11 -0700, "Jim"
wrote:

Most power MosFets have a large Gate to Source capacitance which makes it
difficult to use them at radio frequencies.

It can be done, but the higher the desired operating frequency the
greater effect the parasitic capacitance has, so most designs I have seen
were up to 7 MHz and that was about the upper limit.



Jim Pennell
N6BIU

7mhz was not the upper limit but around 20m the Gate Xc does makes
them harder to drive.

There are a number of designs that run them as linear amps to 10m but
the drive networks take that into account. A pair of IRF510s will do
35-40W in the FARA design published in QST.

Allison