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Tuesday, 7 October 2008


Every QRP OP needs an accurate qrp meter that will work at 5W and less. Many commercial meters seem to need 5W or more to even move the needle. I had to modify my original meter to be able to show 10W as it was a 100W VSWR....

Back in May 2008 I spent a week with Ken Evans and Ted Bruce (and a few other amateurs) at FDIM/Dayton 2008 and they mentioned the NoGaWatt meter so I thought I'd have to try it.

This is a fine example from N5FC and shows how small and neat these really are:

The project docs are here:

At the 2007 GQRP rally Henning Mikklesen OZ4XF gave me a pair of dual meters which are high quality dual channel VU meters surplus from some B&O project that never happened. The scale is 250uA FSD and a little more that the NoGaWatt project so I will adjust things a little.

I used a couple of Ge diodes bought from Harrisons (Local repeater group rally at Bottisham, wx was cold and wet that day and did the round trip 20+ miles by bicycle with xyl!) and two 47 ohm (matched from a big batch) 10W resistors that measured 49.2(ish) ohms. I also have a load of 51 ohm resistors and I have another version using a load in series/parallel combinations to obtain 50 ohm. I switched the trim pots for minature rotary pots after proving the construction worked as I wanted to be able to adjust the scales.

In HB style I have used Double sided PCB to fabricate a sloping front box, I was going to try and use the humble backed bean tin ( but didn't have enough as the green bins were just collected and xyl threw out my stash of tins. The meter being almost 4 1/2" across meant this was never going to be an Altoid project.

I initially wound the FT50-43 with 24SWG wire but will replace the single turn with a length of RG174.

I have a load of 50 ohm 100W chip resistors so adding on as a dummy load. Put 4 out just to see if would fit as also available in smaller 10W variety also TO220 so would put them on back with a switch of the VSWR meter and have a dummy load too.

Pics of my construction follow:

I am also playing (right word?) with PIC variations and I have some 2x40 (yes 40) character displays from Diz W8DIZ and I have an initial PIC VSWR working that shows the fwd/rev and VSWR as figures on the left and moving bar graphs. When complete and stable I'll add the details. I am using a 16F874A (same as 16F877A but 1/2 memory).

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