I discussed a QRP(p) meter a couple of times by e-mail with Hans PE1BVQ. The main advantage with this kind of meter is that you can actually read QRPp power levels. When using a power attenuator it's just guessing and I'm afraid you loose some receive capability when not using a TRX switch. I prefer to adjust the power with my audio from the computer. Well, searching for a very simple QRPp power meter or indicator didn't bring me much. Too difficult, too complicated. I wanted a 10 minute job as I'm always running out of time. Now I had a book from G3BDQ called "practical antennas for novices". A very usefull book....for novices and most of the subjects are known already now. I sold it via the dutch internet marketplace, but just before I wrapped it before posting to the new owner my eye felt on a page with a very simple QRP power meter. Just what I searched and I made a copy for my own use. I took my old SWR/pwr meter and soldered some wires and components like advertised. To calibrate I first tried on 1W and adjusted the meter full scale, did check 0,5W and the meter was reasonable accurate. Then I lowered my power to 100mW and set the meter to full scale. I'm now able to read 10-100mW very reasonable. QRPp meter ready, my first homebrew project of 2014 ;-). I'm using a 100 microA meter instead of a 1 mA meter as that is what is in my old SWR meter, the diode is a germanium type that was in the meter already and not the 1N4148 diode. The 22K potmeter is a 50K potmeter in my meter as that is what was already in there.
Results so far with 10mW WSPR:
On 10m I used the HB9CV beaming 150 degrees. On 80m of course the horizontal loop.
|A bit foggy...notice the 2K2 resistor.|
|As before, only full scale is now 100mW instead of 10W|