I ended up with an old straight key that has a curious feature: below the main arm that you would tap on, there's an extra metal flange that can sort of loosely pinch an extra sliding lever underneath, basically like a knife switch tipped over:

Extra slide switch on an old straight key

When moved into contact, it simply shorts the two terminals of the key. So I guess I could use it when trying to heat up an SWR meter or something, but otherwise it seems sort of useless, something you'd accidentally bump on at an inconvenient time.

Is my key wired up right? Seems more reasonable that this would be handy to disable a key that wasn't in use, but it sure doesn't seem like the electrical layout supports that. It seems intentionally designed to do the opposite, i.e. locking the key "down" instead of "up".

Would a telegraph or radio operator ever really need the ability to leave a "daaaaaaaaaaaaaaaaaaah" signal going indefinitely? Did this have a more useful purpose historically, like in some sort of common multiple-key configuration?


My understanding is that in at least some telegraph systems, the principle of operation was as in this circuit (where the coils depicted are actually telegraph sounders):


simulate this circuit – Schematic created using CircuitLab

Thus, your key's shorting switch is, in radio terms, your transmit/receive switch: you close it in order to listen, and the other side actually completes the circuit with their key as they are sending code. (Note that the other side can detect the state of your key while idle — by checking for voltage across their open key.)

For radio CW transmissions, this part of a key is not useful for normal operation, but you could use it e.g. while adjusting a manual antenna tuner, if your radio does not have a better function for providing a tuning signal.

I haven't heard of anyone specifically wanting this feature in a key, though, except for its historical value.

  • $\begingroup$ Thanks! This confirms what some telegraphy sites seemed to be hinting at, but your diagram is simpler than others I'd found, making the setup much clearer. (Before I started looking into this, I had assumed that somehow any operator could "add" a signal onto the wire, rather than literally completing the circuit on each dit.) $\endgroup$ – natevw - AF7TB Jan 6 '17 at 1:36
  • $\begingroup$ Interesting thinking through the implications of this: in each telegraph office, the buzzer would sound continuously when there was no traffic! Then I imagine when a station was about to send, you'd hear them open the circuit for a bit and then start ticking. (Or if the wire had broken, everyone's buzzer would go silent…in that case, there's actually some interesting "troubleshooting" techniques described within morsetelegraphclub.org/wirechief/#closed) $\endgroup$ – natevw - AF7TB Jan 6 '17 at 1:47
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    $\begingroup$ Hmm, apparently each "sounder" was more of a "clicker" than a "buzzer": youtube.com/watch?v=ID6r4-2_0bc (includes circuit closer!) as well as youtube.com/watch?v=Lki3jxNLVCI. Just how distinct the sounds from these apparatus were vs. the tones later heard with wireless equipment is acknowleged towards the end of youtube.com/watch?v=rriTe-HGrVw $\endgroup$ – natevw - AF7TB Jan 6 '17 at 2:04
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    $\begingroup$ I read somewhere that the shorting switch was the ultimate way of attracting the attention of an operator who was in the middle of sending a long message. The sending operator had a sounder in the same circuit along with the receiving operators, so when a receiver broke the circuit by opening the shorting switch, then the sender's sounder would stop clicking, letting him or her know that someone was trying to attract his or her attention. $\endgroup$ – rclocher3 Jan 6 '17 at 5:20
  • $\begingroup$ Excellent answer, @Kevin. I use a J-38 telegraph key as my main straight key. And you are correct about the circuit. Your diagram shows two stations, and on the railroads there would be multiple stations, so if a station was unmanned they would use the shorting bar to preserve the continuity of the system. $\endgroup$ – SDsolar Aug 18 '17 at 18:32

The switch on the side of the key is or rather was used when tuning up a transmitter. In the old days you had to increase drive and dip the grid of the final amplifier. So this is simply a switch so that the operator can key his transmitter and use both hands for the operation. Today you don't tune like that UNLESS you have a high power amplifier. But this type of tuning will usually draw the criticism from others on the band and is frowned on, and the person operating in this manner is considered a LID (poor operator) and a discourteous person.

Hope this helps


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    $\begingroup$ I use a manual antenna tuner that requires manual knob twiddling, and I don't believe that doing so makes me a lid ;) Of course I know from experience where to put the inductor switch for each band, and I can adjust the other two knobs in two or three seconds tops, and I don't tune up on top of the DX station. $\endgroup$ – rclocher3 Jan 6 '17 at 5:26
  • $\begingroup$ That sounds like you do it smart. I would only call you a lid if you DID tune on-air right on top of heavy traffic. I definitely still hear people do that and wonder why their mama's didn't train them better. ;-) And need I mention that all transmissions are supposed to be ID'd at the beginning and end, and every 10 minutes throughout? Technically, when tuning up the amps it is supposed to be done into a dummy load. Obviously that can't work with the antenna tuner, though. But nobody will complain about 2-3 seconds. $\endgroup$ – SDsolar Aug 19 '17 at 22:40

I still use an antique J-38 telegraph key with my newish solid-state rigs, but I still remember my Hot Water 60 and HW-100 where it was handy for tuning.

enter image description here

When tuning up tube rigs there was sometimes a two-handed job of finding the dip in the final.

So the keys could hold it on in N0 format - true CW.

The origination of the shorting bar was from the old railroad telegraph stations - when they were unoccupied it would allow the signal to go through, preserving continuity of the circuit.

btw, long ago when I used the venerable Heathkit HD-1410 squeeze keyer, you would pull out the speed control to switch it on continuously to peak your finals.

And now, using MFJ-9420 and MFJ-9475 QRP rigs, they have a Tune button on the front panel, for setting up the MFJ-971 antenna tuner, as @Kevin mentioned. I know the basic settings that work with my antennas on each band, peak them for max QRN (or signals) then just briefly use the shorting bar to tune for min SWR.


The shorting arm/bar serves the purpose exemplified by the schematic: It closes one of the two sets of parallelled switches (each of which sets consists of the key-lever-closable contacts in parallel with the shorting-arm contacts) that are connected in series with the system's sounders, thus allowing the distant station to send. (Sounders were not buzzers, BTW; they were, in effect, very sensitive relays that made metallic clicks on MAKE and BREAK.) Use of the shorting arm for radio-transmitter tuning may be more user-friendly that leaning a book or other heavy object on a straight key, but presence of the shorting bar on keys predates the existence of radiocommunication in any form.

  • $\begingroup$ Welcome to Amateur Radio Stack Exchange. Please take the tour at ham.stackexchange.com/Tour to get the most out of this site. $\endgroup$ – SDsolar Aug 19 '17 at 22:31

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