During Field Day 1971 held at the WCHA AM radio site and then Field Day 1972 held at Andy’s mountain farm in Maryland with the Hagerstown radio club, Joe Lochbaum and I operated CW using a straight key and wore our arms out. So, after 1972, I decided to try to build an electronic keyer. Many keyer designs were available by then, but one issue was the need for a set of mechanical paddles which came at a significant cost. A company called Data Engineering Inc sold a device called “The Electronic Feather Touch Key” which I saw at the Gaithersburg Hamfest in 1972. I had started to play around with op amps and transistors and discovered that the input impedance of an op-amp could be 10 MOhm or higher and that very small currents through the skin from a 9 to 15 Volt power supply could toggle the inputs. So, I developed a resistive touch keyer which used a large metal plate where the operator placed their hand and touched DOT and DASH aluminum small fixed plates with the thumb and forefinger to generate CW. Initially it used 6 op amps in dual op-amp packages and a open frame relay to key the rig. The relay was very noisy, but worked with either cathode or grid block keying (positive and negative voltages respectively). I used it first for Field Day 1973 and published the design in the club’s newsletter, QRN, that fall in October, 1973. I think it was the first thing I ever published at age 16. I later changed the output to a quieter reed-relay and made other changes. After I swapped out my Multi-Elmac AF-67 transmitter with cathode keying and bought my SB-101 with grid block keying from Elmer Longenecker, I made some other changes. Eventually I found the LM339 quad op-amp IC that could operate on a single-sided power supply and designed a keyer around it using 3 op amps. It ran off of a single 9 Volt battery and had a solid state output for negative grid block keying systems. I removed the sidetone generator that the earlier designs included to simplify it since the SB-101 and most rigs by that time included internal sidetone for CW.
This is a reconstruction of the keyer built 50 years later in 2025 with a new separate resistive touch paddle. The controls are an OFF-ON-TUNE rotary switch and a speed potentiometer. Inside the keyer box are trim pots to set dot-space and dash-space ratios. It used an original single-sided PCB from almost 50 years earlier and most of the parts were still in my collection of parts from that time, but I did need a new box, parts for the touch paddle, a new LM339 IC and output driver high voltage PNP transistor. It was great fun to rebuild my old keyer design using an original PCB and see that it worked quite well!
CW Keyer in Operation. Operation is fairly smooth.
This is the interior of the reconstructed keyer in 2025. The LM339 14-pin DIP IC quad op-amp is in the center of the PCB. Trim pots for dot-space and dash-space ratios are near the top edge of the PCB. The circuit uses a number of fixed resistors, fixed capacitors and small signal diodes in addition.
The sensitivity of the keyer to touch was a bit weak as designed in 1975 and to keep it very simple there were no sensitivity adjustments. In 2025, I added two 500k trim pots going from ground to the -9 Volt supply with a 5.6 MOhm resistor from each pot center tap to the DOT and DASH inputs (not shown in the photo). This allowed the bias on each input to be adjusted to very close to the trigger point and the touch sensitivity can then be made quite high. With this addition, keying is more comfortable and reliable, but I used the original design for several years in the 1970’s. The aluminum plates can oxidize a bit over time, so periodic cleaning is helpful to avoid operation becoming a bit unreliable. Capacitive touch paddles can also experience this issue and require cleaning. Touch keying devices were never as popular as mechanical paddles, although Heathkit sold a touch keyer model SA-5010 uMatic. I purchased, assembled and used for several years an SA-5010 in the 1990’s. Today, there appear to only be a few kits available from several smaller suppliers for touch keyers.
This document contains the original pages of a short assembly manual that I shipped with a few kits that I sold in 1979. The kits included the PCB and the components for the PCB, including the speed pot. Anyone using the kit needed to get a box for the keyer, a battery, a switch, and a 1/4″ plug, and make a resistive touch paddle.
The PCB from about 1976 is shown below. It was one-sided. I drilled the almost 120 holes per board myself. There was no plating in the holes.
The 1975 touch keyer was used as a prototype for the PCB and final design. I used it for a number of years and still have it in 2025, but it sits on the shelf. I typically use good mechanical paddles with an MFJ memory keyer or internal rig keyers as of 2025.
The interior of the 1975 keyer. It was a pre-PCB implementation using a proto-board, but the design was the same as the PCB design.
The resistive touch keyer design was published in 73-Magazine in January of 1979.