?

Hans

I've just uploaded a file showing my mods to the U2 kit to drive an
external class E PA. My main interest is using the U2 on 472kHz but the
same idea would work for other bands. At present my PA produces about 35
watts of RF which is hardly QRP but when the radiating efficiency of
antennas at 472kHz is taken into account (virtually zero!) then the rig
really is QRP.

The mods to the U2 are as follows:

Remove Q2 and R2.
Replace the toroid L1 with a 12v miniature relay (e.g. 60-1992 from
Rapid). This has a single changeover contact and is easily driven by Q1.
The gate of Q1 is driven as before by the control line PB5 (pin 19) on
the ATmega168. This goes 'low' during a non-transmitting period and
'high' during a transmission.
My class E PA uses a IRF510 MOSFET running at 24v and requires a square
wave driver signal at 472kHz; this is provided from the QOUT1 pin 7 on
the DDS. This is then routed through the NO contacts on the relay during
the transmit period. During the no-transmit period, the relay NC
contacts short the PA driver signal line to 0v.

Hope this might be of interest to other members of the group.

Having butchered my U2, I guess that I'll now have to buy another one
for its proper use!

--

73

Barry, G8AGN