Introduction
With the advent of codeless amateur radio operator licensing, the entry point for the Amateur Radio Service has shifted from Morse code operation on the Novice HF sub-bands, to full priviledge Technician operation on VHF. As a result, many operators wishing to upgrade to HF have not listened to Morse transmissions, as many prospective hams did in days gone by. Perfecting the communications art by listening to the W1AW code practice sessions emenating from Newington, CT on 147.555 mc is not possible with recievers here in the west.

While Morse code is used on the VHF bands, many "VHF only" operators restrict their operating to VHF/FM where the only Morse code heard is the ID on the local repeater, often at nearly 20wpm! Code practice participation on VHF is limited, to say the least.

It has been said that the best way to learn to communicate by Morse code is to "get on the air and DO it". Of course, this can be done by the VHFer earning the 5 wpm endorsement and becoming a "Tech Plus". Tech Plus operators have the same priviledges as the Novice operator in the HF section. The CW operator as a Tech Plus can use the HF rig and get on the air and begin communicating with the new mode. There are many on 40 meter CW doing just that.
Problem No. 1:
What if there is no HF rig? What is an ambitious ham to do? How about an MCW net where that ubiquitous VHF/FM rig is pressed into service as an MCW station? MCW can be received with the HT and scanner now seen in most new ham shacks. "MCW" is simply Morse code tones sent as a "Modulated Continuous Wave" the same way that one's voice is sent with an AM or FM transmitter. All that is required for transmitting, in addition to the afore mentioned FM (or AM) rig, is a good, "keyable" audio tone signal source. Many hams and other listeners on VHF might benefit from these MCW transmissions much as beginning hams did in those "days gone by".
Problem No. 2:
The budding ham operator no longer builds his first reciever for the HF bands to get started. It's just too easy to go to the local "electronics department store" and buy that little scanner or HT. This seems to be true for most other station accessories as well. One result of this easy availability of equipment is that there is less home brewed equipment on the air, and less practical knowledge of electronic circuits in our ham community.

As a possible solution to the above problems, I present here an audio oscillator for MCW transmitting.

Parts list for Oscillator Figure 1

Parts list for Amplifier Figure 2

Design Criteria
There are many ways to generate what could be called an MCW signal. In an emergency any method would result in communication, I suppose. But I think a responsible ham would strive for the best signal one can achieve. Using a code practice set that is designed to simply make a squeeking noise when the key is closed is not suitable for use on the air. The signal from the MCW generator should be a pure tone with a clean sine waveform. This generator should begin and end each character element cleanly with no click, pop or chirp. This is the kind of signal produced in a good receiver when tuned to actual CW.

The common squarewave practice set can have it's signal filtered and thus be made to produce a satisfactory MCW signal, but it might be better to start with a nice sine wave. Building a simple sine wave oscillator is an instructive process and could help eliminate the lack of "practical knowledge" mentioned above.

My search for a good oscillator circuit that does not click when keyed or unkeyed, has no chirp under those same conditions, and does not sound like an accordian with a broken reed, revealed the "Twin-T" circuit shown in Figure 1 .

Connections and Use
Connecting the oscillator to the mic input of the radio can be done through a simple DPDT toggle switch. This switch can be labled for "Transmit" and "Receive". One section of the switch turns off the power to the oscillator, and the other section connects the output of the MCW system to the radio.

Radios of different manufacture have different input and switching requirements. With most of the earlier designs, a simple switch closure will put the radio into transmit. That closure would , of course, be connected to the PTT ("push to talk") connections, just as the original mic is. The audio line can be left connected in most cases on these early radios. Check your actual mic. hookup. Some systems require that the audio line be disconnected also. A 3PDT or 4PDT switch may be required with some radios. Just duplicate the switching that is in the mic.

A few of the modern radios require a low impedance at the mic input to switch into the transmit mode. An open circuit there switches to the receive mode. Radios with "load sensing" mic jacks can be wired as shown in detail "A". The HTX-202 seems to work with 3900 ohms as the load resistor. The value doesn't seem to be critical, but it must be low enough to provide reliable switching, and high enough to allow enough signal voltage into the mic preamp circuit.

You could get fancy with the switching, and provide another switch to allow rapid change over from the MCW oscillator to the normal mic. A "Phone/CW" switch. All of this could be included in a small box along with the circuitry and power supply.

A good operator will want to hear his own sending. If your normal setup has you "duplexing", no sidetone amplifier is required. If not duplexing, a small power amplifier circuit is shown in Figure 2.

Adjustment
It is important that the audio signal level going into the mic jack be set correctly. Do not set it too high. It will sound awful and may cause adjacent channel interferance. If set too low, the signal will be under modulated and hard to copy. The level should be set to about the same level as your normal voice transmission levels, maybe just a bit below that. If a deviation monitor is available, a setting between 3.5 and 4 kc seems about right for the NBFM receivers that we use today.

If no deviation meter is available, a second receiver tuned to your transmit frequency could be used. The output of this receiver can be connected to an audio oscilloscope. Check your normal voice transmission on the scope and note the peak level shown there. Set the peak level of your CW tone to about 70% to 80% of the peak level noted above.

With this test equipment properly setup and adjusted you should see a nice clean sine-wave when the key is down. By setting the sweep slower, you can check for a good keyed waveform on both the rise and fall of each character element's waveform envelope. The components selected in the design should provide both of these characteristics.