![]() The recorded message being sent to the transceiver’s mic input can also be heard through the keyer’s speaker.Ĭ1 is used to isolate the Record/Playback DC voltage from the transceiver. I start with R1 at zero and increase microphone input until the transceiver RF output is equal to the output with the microphone. R1 is a 10K ohm potentiometer used to set the audio input to the transceiver to around 40-50 mV. The recorded message is sent to the transceiver’s microphone input. Relay (K1) simultaneously keys the transceiver’s PTT circuit and “turns on” the playback module. ![]() The Repeat Cycle Timer’s normally-open output contacts are used to energize K1: a two-pole double-throw relay during the On cycles. These cycles continue to repeat as long as the timer is energized. At the end of the off-delay, the On-Delay cycle starts over again. contacts open and remain open for the length of time set by the timer’s Off-Delay potentiometer. When the pushbutton switch turns the keyer on, the Repeat Cycle Timer is energized and its normally-open output contacts close for a length of time set by the On-Delay potentiometer. A DC-DC “buck” voltage regulator supplies power to them whenever the keyer is on. ![]() The Record/Playback Module and the Repeat Cycle Timer are both 5 VDC devices. The 3PDT switch also controls 12 VDC power to the circuit. In the Keyer On position, the switch connects the output of the Record/Playback Module to the transceiver. In the Keyer Off position, the switch connects the original PTT microphone to the transceiver’s microphone input jack. A three-conductor cord connects the two ungrounded contacts of a stereo phone plug to the center pins of a manually operated three-pole double-throw (3PDT) pushbutton switch. Although I designed it for use with a Microbitx (♛ITX) high-frequency transceiver, it can easily be adapted to any transceiver utilizing a push-to-talk (PTT) microphone. The circuit is simple and straightforward. With all the major components available from eBay, I drew up the sketch in Figure 1 to put them together. The receiver would automatically listen for any replies between messages. I could use it to “turn on” the playback message, then turn it “off” for a predetermined period of time before turning it on again.Ī relay could be added to key the transmitter’s PTT circuit every time my CQ message was played. I also found a repeat-cycle timer (variable on and variable off delays) on eBay for $2.38. I found a 20 second record-playback module on eBay for $2.59. For field operation, I could live with a single CQ. Could I get by with fewer amenities and shrink the size, weight, and power requirements to something more backpack friendly? It was worth an investigation. The MFJ-434 has 11 buttons to push, three potentiometers to turn, and two LEDs to show me the keyer is doing what I told it to do. The enormous number of contacts warranted a closer look at a keyer for shorter field trips. What a difference that keyer made! In less than three months, I worked stations in 31 countries and five continents running a 10 watt transmitter and a dipole antenna! Since that stay was planned to last longer than my normal field trips, I decided to take my MFJ keyer for its first outing. Last winter, I was packing a QRP “Go Box” for a trip to Florida. I always run out of voice before I run out of battery. On the other hand, I’m absolutely positive the lack of a keyer has resulted in fewer radio contacts. ![]() An “accessory” measuring 6-1/2 x 7 x 2-1/2 inches fills up a lot of backpack. I have never taken the MFJ keyer, primarily due to its size. Most of the time, it’s important to pack only the bare essentials for these mini-DXpeditions. One of my new favorite pastimes has been operating QRP radios from remote off-the-grid locations. It has been a big asset during ham radio contests and when I’ve been calling CQs with reduced power (QRP) transceivers. I have an MFJ-434 voice keyer that has saved a lot of wear and tear on my vocal cords over the years.
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