DC40B update

January 9, 2011 | Amateur Radio | By: Mark VandeWettering

Previously, I noted that the oscillator on my DC40B kit (supplied by Doug Hendrick’s qrpkits.com was rather sluggish to start. Reading the messages on the Yahoo! groups, it seems that adding additional capacitance to the Colpitts oscillator was the correct fix, so today, I dug some 47pfs out of my junk box and soldered them in parallel to the existing caps on the backside of the board. Now, the oscillator starts right up! I still haven’t the transmitter calibrated, but it seems to work thus far. I just need to put the final transistor in place, and then I can mount everything in the case.


Once the sun went down, I started getting large amounts of short wave broadcast interference (some kind of Christian radio). It appears that this kind of interference isn’t unknown. It appears that I need some kind of bandpass for the input. I remembered that the GQRP had a technical page listing some easy input filters: a few minutes Googling yielded this link which has a bunch of designs which use TOKO inductors. I might even have some of those in my junk box.

Share Button
Be Sociable, Share!

Write a comment






eight + 3 =