Last night I was fooling around with the Colpitts Oscillator found in the Pixie II transceiver.   I realize this is nothing NASA would be interested in but it is winter and this is a perfect opportunity for me to learn something useful in my radio hobby.

Here is the oscillator (Common-Collector Colpitts) , click it for a bigger picture:

This is the nice waveform I was getting on my rusty, yet trusty, Tek 465 scope.  Notice the bumpy parts in the top of the wave form. After some discussion about this with Mike WB8ICN and Jason NT7S, I have been instructed to play with the biasing on the transistor.  It is currently biased with a 47K resistor.  It is my intent to remove that resistor and replace it with a trimmer pot in the 100K neighborhood.  This will allow me to "futz" with the biasing by turning the pot left and right and observing the waveform on the scope.  One other little anomaly I found was although this 7040 Khz wave looks pretty OK, there is a weird 1400 Khz wave mixed in there with it.  You have to look real close.  I don't know if that is a weirdity from my scope or perhaps I have something strange and inexplicable going on here.  A brief flurry of midnight twittering to Jason NT7S (lucky for me I'm on EST and he's on PST)  we decided that I ought to plug in a decoupling cap of 100 nF from the collector of the venerable 2N2222 and ground...just to see what happens.  I have not done that yet, I was working on something else today.

Speaking of weird waves...I was thinking maybe my old power supply was doing something weird. So I measured the output and I am getting just a little over 15 vdc...which is a LOT more than the 9v the Pixie II oscillator likes to see.  So, I decided to dig into the junk box and come up with a neat little voltage regulator.  I had a LM317 in there and this is an adjustable supply from 1.25v to 37v and all you need are a couple of caps and a couple of resistors and you can just regulate voltage until the cows come home.  Here is the schematic of what I am building:

I got this idea from a website I found today.

http://diyaudioprojects.com/Technical/Voltage-Regulator/

It took me FAR longer to find all the parts in my junk pile than it took me to build it.  In the construction of this device I used a good deal of hot glue, square pads, and old telephone cross connect wire.  I think stuff like that adds Mojo.  Here's what happened when I power it up.  The LM317 gets VERY warm to the touch.  I have 15v going in from my old power supply but when I measure between the ground plane and the output pin, I don't see any voltage.  In my design I do not have a  pot installed for R2...instead I am using a SPDT switch to pop in a 2.2K Ohm resistor or a 1.5K ohm resistor.  According to the calculator found on the above website, the 2.2 K resistor would provide me with 13.2v and the 1.5 K resistor would give me 9.4v.

NOTE:  As you can see, I have soldered the tab of the voltage regulator to the board.  This is a NO NO.  It will not work.  The tab of this voltage regulator is Voltage OUT, I have created a dead short here.  I am learning by burning.  UGH.

Project Update - Today I decided to leave the transistor biasing alone, as I wanted to mount the voltage regulator circuit and the oscillator together, and then build out the Pixie II RF Amp.  Here is what my board looks like so far:

This is what the waveform looks like coming out of the oscillator.  I measure it to be about 17 mV peak to peak.

This is what the waveform looks like on the collector of the RF Amp with the circuit keyed and it looks to be about 120 mV P-P.

73 de KB9BVN