www.qrp4fun.de Modifications for the WM-2

Some of the modifications for the WM-1 by Larry East, W1HUE, are already solved in the newer WM-2s. Now you can switch between a external power supply and the internal battery.
Peak power display
Because I don't interested in the on-off LED suggested by Larry I realized only the peak power modification. Additional I don't uses the switch (for switching between the modificated and unmodificated circuit). You can see the circuit in the right picture.
The WM-2 has a little bit different PCB against the older WM-1. But you will also find the right points on the new PCB. In the next pictures you can see
left the virginal PCB, right the two cuts on the PCB,
left the places for all parts and right the reality. Oops, it looks like I installed the capacitor backwards. The marked side is the positive pole, which not be connected to ground.
The round cut on pin 5 I solved before I installed the IC with a drill. For all parts you will find enough place on the bottom side of the PCB.
Revers polarity protection
In the original circuit D3 is placed between the external power supply jack and ground. But what should I do if the diode is burning up after an incorret connected supply. The whole WM-2 is better protected with D3 on a different place. I soldered the diode between the power jack (J3) and the power source switcher (S3). You can see it in the right picture.
By the way, I have replaced the existing barrel connector panel jack with 5,5 mm diameter and 2,5 mm center pin against one with 2,1 mm center pin (Reichelt Elektronik, order no. HEBL21).
BNC flange The sockets of the WM-2 are in original PL-sockets. But nearly all devices in my shack use however BNC-sockets and BNC-plugs, I have replaced the PL-sockets. After something searches I could bought suitable sockets with large flange as second-hand (however new ones). They fit accurately on the drillings and break-throughs of the PL-sockets. Simply looking for sockets of Huber/Suhner, which are labeled "23 BNC-50-0-2/133 NE".