Analog Morse Keyers

Simple electronics fascinate me. You can buy complex commercial equipment and there is no way to

compete with them. But it is fun to see that something very simple can do the job as well.

I saw simple schematics of an electronic keyer from 1948 with tubes and relays in Internet. That inspired

me to experiment with "analog keyers", those without flip-flops and processors and

see, if it was really possible to make practical keyer with timing constants only.

There are three time constants we need to manage in a keyer: dot length, dash lengths and space length.

Dot and space are about equal in length and dash is three times dot length.

In digital keyers those relations are managed by counting.

I build two keyers having the same concept but different practical solution. The keyer has two monostable

multivibrators is cascade and forming a ring, which makes the thing oscillate. The first monostable defines

the mark and second the space between marks. The first monostable has two selectable time constants,

one for dots and one for dashes. Output from the first monostable is the keying data directly.

In the first version I used relays as monostable. The one making marks is driven with emitter follower transistor

but would work also without the transistor. In that case the capacitor values would be 100 times greater and

charging current as well. The second monostable relay is driven directly from relay contacts.

Speed control is made with switching. If both relays are transistor driven, also potentiometers could be used

The second version is made without relays by using CMOS NAND-gates with Schmitt-trigger inputs.

MOSFETS are used as switch. Speed control is with two potentiometers: One controls the length of mark

and the other length of space. So you have to turn two knobs in order to change speed. But the scales are

identical. The knobs shall be in the same position and that is easy. The two potentiometers could be

connected mechanically together as well.

Yes, it is possible to make keyers with analog circuits. In the early days, in 1950's keyers were

quite similar to my relay version but made with tubes. There is one advantage in analog keyers: You can adjust separately

all three time constants and make your own personal CW signature.

Pekka

27.9.2008

OH1TV

added

4.4.2011