6 Band U3S Revisisted

Curt M.

Back in October of 2018 I built up a 6 Band U3S. It worked well but 20m was always disappointing because it only put out 100mW, maybe just a little less. I enjoy watching propagation on 20m but my WSPRLite always put out 200mW without any problems so I set the 6 band U3S aside.  

When I was building my 20m QCX there was a lot of talk going around about a bad batch of capacitors which were causing low power out on the QCX. I decided to order all new caps for the filter circuit on the QCX before I even started to build it. When I was finished it put out nearly 5w so I’ll never know if the ones supplied with the kit were bad but the ones that I ordered from Digikey were evidently fine. At that time I ordered 4 spare capacitors and thought maybe I would swap out the caps in the U3S 20m filter just to see if they made any difference  

So tonight nearly two years later I put the U3S on the bench and tested the output power on 20m. It was just about 100mW but not quite. I swapped the caps out and tested the output power and I’m happy to report that it now puts out 250mW.  I’d always thought that the chances of me getting bad caps with that kit were probably slim so I was never in a hurry to change them out. I can finally throw away those two bags away that I marked, “Save for U3S 20m filter”. I’ve moved those things all over the bench for the last couple of years and I’m glad that they solved the problem. It’s now like I have a new toy. 

None of that was Han’s fault and he quickly discovered the problem and it’s not a current problem, I just glad that my U3S 6 Band is now up to spec.

Curt M.


What is the part number?

Curt M.

I thought these came from Digikey but after the part numbers not bringing anything up on their site, I noticed on the bags that they came from Newark.  If I remember correctly the issue was only with one of these parts but I changed them both out.  You'll need two for each 20m filter if you haven't looked at that for a while.

The 180pf cap is: 

The 390pf cap is: