# Designing a simple CW transmitter/receiver

I'm interested in building my own radios for use on the air. I'm still rather new to electronics so I'm looking for simpler projects that I can build to learn on the way, and I'm thinking that a CW transmitter and/or receiver would be appropriate (unless someone wants to tell me otherwise?). I've been reading the ARRL Handbook and "Experimental Methods in RF Design" trying to find the information needed to build one of my own but to no avail. While there are circuit diagrams available in those texts, even the simplest ones are too much for me to understand (I did read the accompanying text) and I feel like if I were to just build it and have it work, it wouldn't progress my understanding of it at all and I'm not confident in my ability to build something large without error if I don't have the possibility of testing the smaller subcircuits individually.

Looking at the block diagram below, I decided to look into the workings of an oscillator, since it doesn't need any other parts of the radio to function, so it'll be easier to test on its own. I understand how a simple RLC circuit behaves (mathematically), but when it's combined with other components to make a complete oscillator, that's when I get lost.

"Experimental Methods in RF Design" mentions the NE602 IC which has an oscillator and a mixer, making it easier to make a complete radio. Another way I could go is using this for the radio and work on the amplifier and antenna, then replacing the IC with discrete components, but I couldn't find any circuits using this IC that are simple enough that I can confidently build it error-free.

Any advice on the path I should take (be it one I've mentioned above or not) and useful resources to get me started or get past the barriers I'm facing?

Thanks.

• Wasn't there another answer to this earlier? I thought I remember seeing something possibly useful in one of the long answers when I skimmed it, but I didn't have time to actually read it until now, and it looks like it disappeared. – howardh Jul 4 '11 at 0:23

It's been so long since I used my ham license that I forgot my most recent callsign :-) I would start with the ARRL Radio Amateur's Handbook: it has lots of practical circuits from simple to very complex and you can build a CW transmitter from it in an evening. The first one I built, waaay back in high school was Doug DeMaw's Tuna Tin 2: a two transistor CW transmitter that fit on top of a tuna can. It's fun and you will learn a lot. If you're into CW, I'd recommend starting with a direct-conversion receiver since they are very easy to build and work pretty well for CW reception.

These days, a lot of what I used transistors for back in the mid 80's - my high school years, can be done much easier using opamps.

• I'm guessing that means that it won't get any simpler than the tuna tin circuits? It still looks pretty intimidating. Would it work if I just combine this with a buffer amplifier and connect that to an antenna? – howardh Jul 4 '11 at 0:32

To actually use a CW transmitter in the ham bands you would need a license. Further you need to insure that you do not cause harmful interference to other users which could happen because of a problem with the circuit.

You will learn skills like how to wind a coil, how to tinker with a debug a simple circuit to get it working etc. It will not require much time or money.

Once you get it working you can re-use the parts to make a more sophisticated one transistor set. More importantly you will be reusing the skills you acquired getting the first set to work.

• I've tried making a crystal set before, but that didn't really work out. My guess is that it's because of impedance mismatch with the antenna (I just connected it to a set of television rabbit ears antennas with an alligator clip) and the lack of a ground connection. Now that I think about it, it would probably be a good idea to get that working first. I am licensed to use all amateur bands, but not with homebrewed equipment. I know to keep power output to a minimum to avoid interference though. – howardh Jul 4 '11 at 0:20

I've been reading the ARRL Handbook and "Experimental Methods in RF Design"

These are the prime sources for building Ham Radio equipment. Let me assure you that there is plenty of info.

The issue is that building radio equipment, even "simple" rigs, is actually very complex. I have found out that it is not enough to just throw together some parts according to a schematic. You need to understand the underlying theory and have some practical experience. I recommend to read and reread those books, especially the first few chapters in each. And keep trying to build. With time comes experience.

Any advice on the path I should take...

You can order a Pixie II kit on eBay. These cost generally $2.75 or so post paid free shipping. Very cheap! If the first one that you build doesn't work (and this is possible) then order a few more and keep trying. There is a nice one that comes with a case/enclosure for$5.

Find some other hams who also like to build radio equipment, and make a friend! Actually, we would like to have someone to build with.

Your question is seven years old, but this advice still applies. Good luck.

• Answers here need to be factual and self contained; this is basically general advice for where to look, which illustrates why the question itself wouldn't be allowed on the site if asked today. – Chris Stratton Dec 20 '18 at 21:14
• Chris - maybe the "rules" need to be relaxed for this particular Stack Exchange site. Wait, I thought I was in Ham Radio. I am in Electrical Engineering. So I agree with you here. – Baruch Atta Dec 20 '18 at 21:39

Once all of the other aspects of the XMTR or RCVR are understood, an oscillator can be built by creating a feedback loop on an amplifier, then either using an LC tank circuit to tune it or a much more precise 3-pin quartz resonator (or just a 2-pin quartz crystal). Thank you for the question, as I have been looking into building an XCVR as well.