The little oscillator that could

I am continuing on my 2n2/20 build. With some wailing and nashing of teeth I have finally gotten the product detector, crystal filter and RX oscillator done. Here's a picture.

The crystal filter and product detector are in the rear (where the toroid with colored wires lives, where the camera is actually focused) and the RX Local Oscillator is in the foreground.

A little history. I built the product detector a few weeks ago. The big issue there was getting the toroid wound and all the wires color coded. That took ol' shakey (me) several hours. I put everything away for the weekend and came back to work on it a week later. There was no toroid to be found.

What happened? Where did it go? Did I misplace it? Did I...oh yeah, this is probably the work of "clepto cat" (aka "Missy" - full name: "Misadventure"). Missy likes shiny things. She takes them and, apparently, saves them for her retirement or something. Anyway, I was sure I was a victim of clepto cat. I looked all over the shack, but no luck. However, that's not surprising because she usually takes things as far away from the scene of the crime as possible. She does this to confuse the people from CSI.

I finally gave up looking for the toroid and spent another few hours winding toroid version 2.0. That's the toroid with the colored wires that you see in the picture. Got it all wound up and installed all the parts for the product detector and crystal filter. Later that night I found toroid version 1.0 stuck behind the network switch that lives under my desk. Dang clepto cat.

I was getting pretty tired of digging cat hair out of my soldering iron. So my lovely female spousal unit (Sue) got me a special Valentine's day present: she made me a "clepto cat guard." Here's a picture of my workbench without the clepto guard:

Here it is with the clepto guard in place:

Pretty sexy Valentine's Day present, huh? It's made from a science fair presentation board that she fancied up. It seems to work, so far.

So I continued with my build. I built the RX local oscillator next. It was a pretty easy build, even though it was a little cramped. All went well until I fired it up. I was able to see the oscillator working on my scope, but the signal was not strong enough for my freqency meter to pick it up. What's wrong? My scope said that I was only getting about 100mv p-p. Using my advanced liberal arts major math skills, I think that translates to about a -30dbm. The schematic said I should be getting a+7dbm signal out of the oscillator. What did I do now?

Mike, WA5PSE, said I might be using the 10:1 scope lead. Nope. I did some quick and dirty scope calibration checks and it was reading correctly [i.e.: close enough]. So I started following voltages around the circiut. Everything seemed healthy until I worked my way up to the "output" at the L8-R55 junction. That's where everything seemed to shut down.

I looked to see if I had the proper value components at that spot. The resistor was OK. And the inductor was the proper 27uH value. Wait a minute, that seems a little high. So I squinted at the schematic under bright light. Sure enough...what I thought was supposed to be a 27uH inductor was actually supposed to be a 2.7uH inductor. Oh man.

I replaced the 27uH inductor with a 2.7 uH. Yeah, that makes a difference! The scope now says I'm getting out about 1.6v p-p; .8 v peak; .56 v rms = +7 dbm (about). Am I a techno stud, or what? Here's a picture of the oscillator running with my freq. meter attached. I knew you'd be interested:

TC7 seems to adjust out that extra ".12" - but I'll deal with that later, if need be.

See. You thought I couldn't do this, didn't you?

73

72

WA5PSA

2N2/20 Build

Mike and I have been building K8IQY's 2N2/20 transceiver for awhile. I got off to an early lead. But Mike shot on ahead. OK...I'm slow.

The 2n2/20 is a 20M transceiver. CW only. 5 watts. Built using the manhattan style of construction.

Here's where I am right now.

Pretty impressive, huh? Yeah, I don't think so either.

Obviously, most of my progress is along the west side of the circuit board. This is all of the receiver audio circuitry, including the receive mute switching circuit. In the upper right hand corner lives the transmit/receive switching. The empty pads are for the roofing filter and product detector.

Here's another shot of the product detector and audio pre-amp. This shot helps you understand why this is called "Manhattan" style construction. Because it looks like you could get mugged down there. No, actually, seen from the side like this, the components look like a city skyline. It also looks like I need to figure out how to take macro pictures with good lighting.

Here's an aerial view of the audio preamp. See the four diodes lined up over in the product detector section? I've wound a toroid that will snuggle in right next to those diodes. Let's see if I can take a better picture of the board.

Not too much better. Oh well.

I just got through winding the toroid that will live just to the right of the four diodes that are standing up near the center of the photo. That installs next.

73

WA5PSA