Moving Forward with A 40M Transmitter

The Idea

In a desire to build something to get me on the air, I've taken a step back from the 80 MMM and have decided to move forward with a 40M transmitter. Bill Maera recommended aiming at the 10 Minute Transmitter.  Quite sure this was on Bill's mind when posting Ciprian's version.

I decided to not build a low pass filter for my 80M MMM. My thinking: I'm a parts cheapskate and I really won't be using the 80M MMM to get on the air. Yeah, I wanted to see an improvement of the carrier wave on the oscilloscope, but I'll be doing this for 40M, right?

I collected some parts, ordered a few too. Bill recommended trying any NPN transistor that I had in inventory, so I'll thought I'd mock up the transmitter using a 2N2222 or 2N3094. What's the worst that can happen? I mean, there is the word "smoke" in the Solder Smoke podcast name. 

Here's the design(s) that I used:

Original 10 Minute Transmitter by Steve (G4RAW)


 

Walter (KA4KXX)'s version as seen in the Solder Smoke blog..

And here's my parts:

• 100uH coil.*
• .1uF capacitors (2)
• 240 pF capacitor**
• 7.123 MHz crystal
• 22K resistor
• 2N3053 transistor***

* Using 37-43 toroid, that's about 16-17 turns as indicated in winding data found on Kits & Parts.

**Walter (KA4KXX) has adjustment instructions on the Solder Smoke blog: please be advised that the way to tune the "240" pf series output capacitor is to first connect a 50 ohm dummy load to the transmitter and peak the RF Output Voltage. If there is no defined peak then temporarily use a variable capacitor with a wide range because your value may be much different than mine since you are using another transistor, circuit board layout, etc. Also, note that in my version I connected the transmitter to a multi-stage antenna tuner before attaching that to my end-fed antenna so my signal out of the antenna was probably very clean. . 

***Other NPN transistors such as a 2n2222 or 2n3904 should also work.

The Trouble

I breadboarded the circuit and... Nothing. Like absolutely nothing. 

Now, those who grew up in 70's and 80's remember the teen biopic The Breakfast Club. In that movie, the nerdy teen who found himself in Saturday detention reveals his biggest failure: he couldn't make a lamp in shop class. You know where this is going: I felt like that kid. The 10 Minute Transmitter That Took Two Days to Build. 

No worries. I now like to think that I'm grown up and laugh at myself, my abilities (or lack thereof), and some of life's little foibles. Be that as it may, Bill relayed some troubleshooting hints:

On this project you might need an antenna or an antenna substitute.  Just put a 50 ohm resistor from the variable cap antenna connection to ground.    Then try getting it going while fiddling with the variable cap setting. 

It should work with 9V.   But maybe try a fresh battery.  

To check the voltages -- keeping the key up, the voltage on the collector of the transistor should equal the voltage of your power source.  

If you've let the transistor get too hot, try with a new transistor. 

Make sure you have the leads right on the transistor,  It is usually E B C facing the flat part of the transistor,  It is easy to get them backwards. 

I think Walter was talking about peak output voltage.  Don't worry about that for now -- you just want to get it oscillating.   

Make sure your receiver is on LSB or SSB or CW (not on AM)  Tune around a bit as you fiddle with it. 

Peter Parker did a video on this: https://www.youtube.com/watch?v=cPPi7uLGtgY

Perhaps more useful is this: https://makerf.com/posts/ten-minute-transmitter

Hang in there.  Let me know how it is going. 

Of course, I didn't stick to one set of variables. I did several things--all or some of which may have made the difference:

1. I moved to 12v power. Actually, I used 13.8v and powered through a plug so that I could use my normal rig power supply or LiPo battery from portable operation. Pinout reminder:

 

2. Most importantly, perhaps, I ditched the breadboard. Chances are some small connection is broken or I failed to visualize a vertical connection. "Time to melt some solder," said Bill.

3. Added a variable capacitor so that I could adjust peak output at some point.

Here's what my project looks like:

And We're In Business

We're oscillating, folks:

Project Description

Successful Oscillation