What is the difference between Iambic Keyer mode A and mode B? Are there any other popular keyer modes? Why would one choose one mode over the other?

If only one Iambic keyer mode is to be implemented, which mode should a keyer that supports only one mode support (in the U.S.)?

  • $\begingroup$ There certainly is no rule on this, so asking which you "should" use is really opinion-based. I can use any kind of keyer so to me it wouldn't matter. In the end they can sound the same on the receiving end. The main difference is that you can hear the "fist" of someone on on a semi-automatic keyer - I remember one guy who used to draw out his dahs quite a lot longer than the fully-auto keyers would do, so we could recognize it was him before he even gave his callsign as he sent out CQs. Is that what you mean? $\endgroup$
    – SDsolar
    Sep 18, 2017 at 7:49

1 Answer 1


An iambic keyer is used with two paddles. The concept is that you can hold down one paddle, say the dah paddle, to send out a string of dahs. While doing this, if you tap the dit paddle, it will insert a dit between the dahs.

If you hold both paddles at the same time, the iambic keyer will send alternate dits and dahs. The difference between mode A and mode B iambic keying is what happens when you release both paddles. In mode A, the keyer will finish with the last dit or dah that it was sending at the time of release. In mode B, if it was sending a dah when you release the paddles, it will add one more dit. If it was sending a dit, it will add one more dah.

It is widely held (no pun intended) that mode B came about because of a logic error on an early iambic keyer. Operators got used to the effect and then found it difficult to use a corrected (mode A) keyer. As a result, most keyers offer the option to switch between mode A and mode B.

The first keyer I used was a Heathkit unit that was mode A. When I try a mode B keyer, I am often making sending errors. There is no right or wrong mode - both are well established. The receiving station cannot tell the difference. It is down to a matter of operator training and preference.

  • $\begingroup$ Glenn, I am not familiar with calling them Mode A and Mode B, but did start out my keyer days with a Heathkit HD-1410 which was full iambic- both dits and dahs were self-completing, as opposed to the mechanical bugs which we called semi-auto. The difference was that the semi-auto (mechanical) bugs had self-completing dits but you had to time the dahs manually. And yes, the Heathkit had two pieces, one for each finger, but the bugs were one-piece that you moved horizontally. Is that what you are referring to? $\endgroup$
    – SDsolar
    Sep 18, 2017 at 7:45
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    $\begingroup$ @SDsolar Your Heathkit sounds like the one I had. I later added external paddles to get more adjustability. I believe it was a mode A only keyer. $\endgroup$
    – Glenn W9IQ
    Sep 18, 2017 at 20:29
  • $\begingroup$ Just for fun, check out this project that uses finger capacitance to make an iambic keyer. (I prefer the Heathkit or Bencher paddles where you can feel them) - but this is a cool project nonetheless, and just takes a few minutes to build: jel.gr/cw-mode/iambic-keyer-with-arduino-in-5-minutes $\endgroup$
    – SDsolar
    Nov 3, 2017 at 20:32
  • $\begingroup$ Found a good article about Modes A and B: ag6qr.net/index.php/2017/01/06/iambic-a-or-b-or-does-it-matter and now I see that with the Heathkit I never actually released both paddles at the same time, so I could guarantee which final element got sent with the Heathkit. It is pretty natural and by operating it this way the mode difference makes no difference. If I was to release both simultaneously then it would be pretty important to me that it be Mode A - simply complete the element being keyed. Your answer is excellent in explaining the difference.. $\endgroup$
    – SDsolar
    Feb 27, 2018 at 23:03

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