Tuesday 23 April 2024



I’ve been looking for a nice little QRP WATT METER for ages and it seems like no one makes one any more. MFJ’s 813 has been discontinued and any retailer who has one left on their shelf is asking stupid money - and it’s not that good anyway!

So when I spotted this rare Lake Electronics PM-20 at last weekend’s radio rally, I quickly pounced on it and forked out a tenner to make it mine. It has two measurement ranges : 0-1000mW and 0-20W. 

It seemed to be in mint condition and I couldn’t wait to get home to try it out. Sadly, things didn’t turn out too well, because it wasn’t working - at all 😓

I opened up the case to see if there was anything obviously wrong, but the inside looked even better than the outside, so I closed it back up and emailed one of Bolton Wireless Club’s members to seek help. Ross (G6GVI) very kindly offered to have a look at it during the next Club Meet.

At the Club, Ross explained where I should take some DVM readings and provided me with some additional guidance in the form of circuit diagrams. He also gave me a diode in case that was part of the problem.

Tonight, I reopened the case and briefly put a continuity meter across the PM-20 meter terminals to see if the coil was actually functioning and sure enough, the needle went full scale. Great! Before doing anything else, I decided to swap out the diode with the one Ross had supplied. I’m happy to report that the meter is now working!! 👌

I then spent some time adjusting the pots to get a readout which matched the indicated output of three QRP transceivers.

I’m really pleased to have this meter up and running and I thank Ross for his valuable help.

73 de Tom, M7MCQ.

1 comment:

PE4BAS, Bas said...

Very nice Tom, I love these kind of meters. In the past I made my own mW QRP meter which also measured I believe in the range of 1000mW. This one is big enough and very good readable. 73, Bas