Introduction

Here are a few odds and ends that don't easily fit in any of the other catagories.

Bug Key

This idea was included in a article by J. Worthington, GW3COI, in the August 1988 issue of Practical Wireless.

A keyer is really split into two sections. There is the Keyer Logic that connects to the key. This is usually the low level logic (TTL/CMOS) that takes care of generating the dots and dashes. Then there is the Keying Interface. That interface takes care of converting the logic level dots and dashes, to whatever is required by a transmitters keying input.

Normally, the keyer takes care of all the dots and dashes needed. But some people like the old method of using a Bug (Semi-Automatic Key). With a Bug, the dots are automatic, like a keyer, but the dashes are manual.

The diagram shows how you could implement a Bug Mode with almost any available keyer. That is, as long as you are working with a Common Cathode connection to your transmitter.

The Dasher

If I'm going to include a way of using a keyer in a Bug Mode, I should also include a way of using a Bug in a Keyer Mode.

This idea was included in a article by Joseph H. Fenn, KH6JF, in the March 1979 issue of Ham Radio Magazine. It's intent is to modify the Dash contact so that automatic Dashes are generated. The Speed and Weight of the Dashes is fully adjustable, so that it matches you usual style.

The only change needed on a Vibroplex Bug is to disconnect the lead under the base, from the Dash contact post. Then, Use a two-wire shielded mike cable to provide three connections from the Bug to the input of the Dasher.

The author used the Dasher with a 9 Volt Ni-Cad battery. External screw terminals were used so that the Dasher could be connected to a external charger.

Note: Do not ground any of the 9-volt points to a ground that is common to the relay output or the Bug common lead. RF can get in to the Dasher and cause erratic dash lengths. A couple of ferrite beads on the input and output leads should cure the problem.

Bug Dasher

I have had this schematic in my files for a long time, but have somehow lost the name of the originator. I would guess that this circuit was in QST or 73 Magazine, but I haven't located it yet. When I find the name of the originator, I will give appropriate credit.

With the previous item, The Dasher, you needed to disconnect the leads in the base, so that the Bug would have three wires. One wire for Dots, one wire for Dashs, and a common wire. This circuit doesn't require modifications to the Bug.

• ON time Formula, T1 = 0.69 * RA * C
• OFF time Formula, T2 = 0.69 * RB * C
• The total time period, T = T1 + T2 = TON + TOFF
• T = 0.69 * RA * C + 0.69 * RB * C
• T = 0.69 * (RA + RB) * C
• Here we get a Duty cycle, D = RA/(RA+RB)
• Duty cycle in %, D = RA/(RA+RB) * 100

Normally, without D4 in the circuit, the 555 Astable Mutivibrator circuit can only generate an output which has a duty cycle above 50%. Due to the charging resistance is R3+R4 and discharging resistance is R4, the T1 or the ON period will be always greater than the OFF period. Thus a duty cycle below 50% is not possible with the normal 555 Astable circuit.

So in order to charge and discharge the capacitor through different resistors, a bypass diode is added in the below circuit. Hence, during charging the Diode D4 bypass the resistance R4 and the charging current flows through R3 and D4. And the discharge as same as normal circuit through the R4.

The two wires from the Bug are connected to the Dot/Dash and Frame input (upper left of the schematic). When the Bug is idle, the input is open and R1 holds the input "High". This "High" level is inverted by U2-3 and is applied to the Reset input of U1 (Pin 4). In this Reset condition, the timer output, U1-3, is "Low".

You will note in the schematic, that R3 and R4 have no values listed. This is because their values depend on your intended operating speed, in WPM.

The 555 Timer is configured as a Astable Multivibrator.

Duty Cycle  =		Tm	=	R1 + R2
		Tm + Ts		R1 + 2R2

As shown in Figure 12, adding a second resistor, RB, to the circuit of Figure 9 and connecting the trigger input to the threshold input causes the timer to self-trigger and run as a multi-vibrator. The capacitor C charges through RA and RB and then discharges through RB only. Therefore, the duty cycle is controlled by the values of RA and RB.

This astable connection results in capacitor C charging and discharging between the threshold-voltage level (≅ 0.67 × VCC) and the trigger-voltage level (≅ 0.33 × VCC). As in the mono-stable circuit, charge and discharge times (and, therefore, the frequency and duty cycle) are independent of the supply voltage.

Possible changes might be to eliminate U2 and replace it with a small transistor and resistor.

A Debouncer for Semiautomatic Speed Key - Dave Cuthbert, WX7G, Hillsboro, Oregon

I've noticed that most bugs have "scratchy" sound. A quick look with an oscilloscope showed that "bug" dot contacts usually bounce two or three times at the start of each closure. My solution to this was to build a pulse stretcher that ignores any contact bounce that occurs within 10 milliseconds after the initial closure.

The circuit uses a 4011 CMOS NAND chip and an IRF511 60-volt, 3-ampere MOSFET. The four gates in the 4011 are connected as inverters. When the telegraph key is closed, the input of U1A goes low. The output of U1A goes high and charges C2 through D1. The discharge path of C2 is R3. The time constant of R3 and C2 causes U1B's output to stay low for 10 milliseconds after the key opens. U1C and U1D invert the signal to drive the gate of Q1. The 220 Ω gate resistor prevents oscillations and must be mounted near Q1. If you want to key a cathode-keyed rig, you'll need to use the 400-volt MOSFET, such as an IRF730. C1 attenuates RF energy entering the box and R2 protects the CMOS chip against static discharge. The circuit is powered by a 9-volt alkaline battery, and draws so little that the battery should last for years. All of the debouncer's components are available at Radio Shack if you use an IRF511 instead of the IRF530. - Dave Cuthbert, WX7G, Hillsboro, Oregon

The original article on this circuit can be found in QST Magazine, September 1992, p. 87.

AFC 1290k