2N2/40 Project


Intro Well, Jim Kortge, K8IQY designed this great radio and lots of QRP-L-ers are working on it. Bob Hightower, KI7MN, came up with a board kit. Jim used a construction technique called "Manhattan" construction to build the rig, so the board kit is a little odd. Basically, it's a piece of copperclad with the parts locations screened on it - no holes, no etching. Bob also included some strips of copperclad to make the little pads (officially to be made with an Adel nibbler, but as usual, I had to cheat.)

In addition, Chuck Adams, K5FO, matched some sets of crystals and donated them to be sold with the board kits. This project was to support the Arizona sQRPions. The KI7MN kit is shown at right.

The Board

 

At the left is a picture of the board. The rig involves 22 transistors, all 2N2222's. The radio is constructed by wiring between pads glued to the copperclad with cyanoacrylate glue.

Pads

 

Below is a closeup of the pads glued to the board. I didn't make the pads the 'official' way. For most of the pads, the strips Bob sent were just the right size I could hack off a pad with a tin snips. OK, ok, they're all not exactly as uniform and pretty as Jim's, but hey, this is supposed to be homebrew.

Completed Glue Job

 

The first step is to glue all the pads to the board. Since I don't have all the parts yet, I can go ahead and do this without being tempted to rush.

Well, even so I got a little sloppy around the PA area. 'est la vie.

Frills

 

I got a little concerned about peeling the glue when trying to solder to those pads, and also wondered whether I had gotten cyanoacrylate on top of the pads - it's clear so you wouldn't see it.

Seemed logical to tin the pads - this let me discover how sloppy I had gotten with the glue, and satisfied me that the pads would be solderable when I was trying to attach a toroid.

Next steps

 

Well, now a little wait for parts. As I progress, I'll try to record what I do and report the results here.

Fitting the case

 

One of the first parts to arrive was the case. This was a good thing since it made me realize I probably wanted to fit the board to the case, drill mounting holes, etc. before I had the board filled with parts.

As you can see, it's a fairly tight fit.

Rx/Tx Driver

 

The first part Jim recommends you construct is the Rx/Tx driver circuit. This is pretty simple, as you can see, and fairly easy to test. It's a simple switch, when you ground the key line, the transmit line goes high.

VFO

 

Now on to the VFO. This was a little more challenging, complicated by the fact that I didn't yet have the T7 toroid, which had to be ordered separate from everything else. I recalculated the toroid for a -2 core.

Apparently my calculations were wrong, because when I applied power, I couldn't find an oscillation. Eventually I discovered it way low in frequency, but after a few cycles of desoldering, remove turns, resolder, test I finally got it to oscillate in the right place.

And here's another view of the VFO which gives you a little better idea of just how tight it can get in there.

 

Oh yes, here's a picture of the cute ten-turn pot I found at the Midland Swap.

Front end

 

Next is the receiver front end. Pretty straightforward, although I took a break in the middle and skipped some parts. Took me a while to figure out what was going on.

Crystal Filter

 

The crystal filter proved to be a little more of a challenge than it looked. Perhaps I was getting a bit cocky and didn't plan things out as well as I should, but it seemed awfully tight for as few parts as were there. I was also right up against the edge of the board, and fighting with the front panel controls for air.

IF Amp, Mixer and Audio Amp

I was sort of surprised when I went through all my pictures that I didn't have entire views of these pieces. There were a couple of interesting details, however.

 

You really need to plan out just how you are going to lay out the parts for each section before you start. Bob's boards outline the major parts, and Jim's page has placement diagrams for all the parts, but they are 2 dimensional. They don't tell you that once the crystal is soldered in you won't be able to get at that transistor, or that the resistor has to go over the diodes.

 


I also found in a few places, this one in the audio amp, that there were jumpers short enough that it was hard to strip the ends off the wire and leave insulation between. Here I opted for thick bare wire and relied on the height of the pads to keep it away from ground. Well, I got squeamish when I saw it so I painted the copperclad underneath with clear nail polish just in case.

 

Transmit LO, Mixer, Amp

Well, things get a tad tight in around the transmit local oscillator and mixer.
It got especailly bad when I discovered I was lacking a jumper. At this point, I wasn't being quite so careful about checking the parts diagram aganst the schematic. Several times I thought Jim was wrong but after some emails, I discovered he was right after all. So this time I didn't catch a jumper that, in fact, was missing from the diagram.

 

Of course, I discover this in one of the most crowded parts of the radio and it borders on impossible to thread the jumper through the parts and reach way down in there with the soldering iron! The rascal is the fine red wire toward the left of the picture. You can also see the cermet trimmer on the right that caused me so much grief.

 

Transmit mixer All I could find at first in 100 ohm was s 20 turn cermet - sort of overkill for the purpose. Worse, it's hard to mount, and my mounting job let go while I was tweaking up the PA. Without a ground the PA took off and toasted the finals. Took me a while to figure out what was going on. Oh, I knew immediately that the finals were history, what took me a while was figuring out why. I didn't catch the air under the ground end of the cermet.

 

On to the final

Transmitter driver The transmit driver was a piece of cake - wide open, lots of space. The PA was a whole 'nuther animal, however. All I could find for the tank caps were ancient micas that were absolutely huge. Sandwiched inbetween the toroids there was no room to work.

 

Transmit driver and finals But, eventually it came together, and surprisingly enough, actually worked!

Panel

Front panel Making a decent looking panel is always a bit of a challenge. I cheated here - I cut a piece of Plexiglas and backed it with some glossy card stock on which I had printed the legends. Although it's a bit of a pain to assemble and disassemble, it's pretty servicable.

 

The Completed Board Complete board

 

Hokay, at this point, I'm on the air. The board may be pretty usgly, but boy does this radio work nice. There is so little noise, I was convinced I didn't have enough gain, but the stations pop right out. It's smooth and really feels good. I did add the RIT board (but no pictures of it yet) which I built on regular perfboard. That turned out to be a bad move, so as soon as I get some time it's getting rebuilt Manhattan style.

 

Log

I thought it might be nice to list the first few Q's. There's not a lot here because I seem to have a million things to do, and of course, I keep having to make one more tweak!

Date Time Call Name His Mine QTH 20-Jul 01:37 W8LSS Bob 419 449 Midland, MI 20-Jul 22:50 W3BBO Bob 549 559 Erie, PA 22-Jul 00:03 WA8RXI Rick 589 579 Taylor, MI 22-Jul 02:35 K4SGQ Gil 459 329 near King George, VA

 

Complete with RS phones and Whiterook paddle


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27 Dec 2004


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