Salvaging old CB’s for QRP Parts: Part 1

Salvaging old CB’s for QRP Parts: Part 2

Finishing a QRP Guys Para40Set

A few weeks ago, David KA4ZUC posted on the QRP Amateur Radio Facebook group: He was unable to finish his Para40Set radio kit because of some physical limitations, and asked if he could pay somebody to wind the T1 toroid for him. Apparently, another ham had done so for a fee, but did it wrong. Back to square one.

Not being afraid of winding inductors, I offered to do it for the price of shipping. After some discussion, we agreed that he’d send the whole kit over and I’d finish it, tune it, and test it. Here is the radio:

Unfortunately, the only picture I took is the one above, in its mostly finished state. If you look carefully, I added a 7040 crystal to the radio. I learned after the fact that this was pointless, but I left it rather than desolder it. T1 had 29 windings follows by 5 and 5 windings, all separate. I wound them together just as you would on a QCX. I soldered the potentiometers to the board with short wires for jumpers, and then powered it up. Nothing.

No Power

I traced the circuit and found that a diode was missing. After placing the missing diode, it fired right up. Once I realized that it would only work with headphones, I was in business!

The Tune Up

Tuning the radio was simple, but only after I figured it out. The instructions say to listen to another radio at 7.0mhz and see if you can hear the oscillator in the Para40set. I could only hear it down in the 6.5mhz range, and could only adjust it for the top end range being just below 7mhz. Once I realized that the oscillator is just a basic LC circuit, I removed a turn or two from the 29 turns on T1, and it was instantly in the correct ranging, tuning the whole of 40 meters. Since David is a General, I tuned it for 7030 and up.

Another lesson learned with this little radio is to pay attention to detail. When testing its output, there was none! I got out my magnifier lamp and looked very closely at every component. Aha! There it was: I could see daylight through a solder joint. I filled in more solder, touched up some of the more questionable solders, and tested it. Paydirt! 4w output.

Conclusion

I’ve never built an all analog rig such as this, and I have to say that finishing it off was a lot of fun. I’m glad I took the opportunity to help another ham. I learned something, and gained a friend in the process. Isn’t that what ham radio being a decent human being is all about, anyway?

I hope you enjoyed this post. Please don’t forget to subscribe, or share this with a friend. Thanks and 73!

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