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.) $\endgroup$ 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) $\endgroup$ 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 $\endgroup$ 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
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    $\begingroup$ 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

Land line telegraph keys are fitted with a circuit closer switch. Radio telegraph keys were not but many radio operators used land line keys because they were so readily available. This includes the rather ubiquitous J-38 about which more will be found below. The arcing that occurred at the key contacts of the early spark radios caused radio stations to switch to purpose made keys which had more robust contacts and in some cases arc shields. In North American practice the idle condition of a land telegraph line was with a current of ~60 - 90 Milliamperes flowing continuously and the ferrous metal armatures of all Relays, Main Line Sounders, and Registers, were used, pulled to their energized position by the magnetic flux of the Electromagnet which is part of all Land Line telegraph receiving apparatus. As others have indicated the receiving apparatus were in series in the lines which passed through each station. When the line was idle the continuous current flowing through the line had to pass through each set of Relay or Main Line Sounder electromagnet coils in series.

The earliest batteries used in land line telegraphy were Gravity Cells, so called because the only thing separating the two liquids that made up the batteries electrolyte were the difference in their specific gravity. In order for those Gravity Cells to remain functional they had to be making current continuously. If the circuit was opened for any long period of time the specific gravity of the 2 liquids would become too similar and they would then mix rendering the battery useless until the output was reestablished and the two liquids would separate after the passage of sufficient time. That was the largest factor in telegraph lines in the North America being normally closed constant current systems because they started out that way.

If any telegrapher left their circuit closer open while they were not transmitting it would cripple the line. Without all other circuit closers being closed no operator could take control of the current flow to transmit a message. By opening the circuit closer switch the telegrapher took control of the line and caused all of the other sounders on the line to de-energize. The absence of current flow through the electromagnets of all of the Relays and Main Line Sounders, connected in series in the line, would result in the loss of the magnetic flux generated by each set of coils thus releasing the armature of the Relays and Main Line Sounders to be pushed, in the case of sounders, or pulled in the case of ralays, to their relaxed condition by their return springs. The single click made by the Sounders when the return spring pushed the hammer bar up against the limit stop of their frame alerted the other stations' operators to listen for their station's call to see if the message was for them. If they heard their stations call they would open their keys circuit closer and the operator who was sending their call would know that because the sending operators sounder would go silent in the up posotion. The telegrapher who called the station would then close their circuit closer to allow the other operator to respond. Occasionally the operator who opened the line would be someone other than the station called. This might be done by a telegrapher with urgent traffic such as a railway dispatcher controlling the movement of trains or, especially during World War Two, an operator who needed to send an Army Flash message.

The J-38 Telegraph Key is a US Army Signal Corps LAND LINE key that was already in use when the United States entered World War Two. Every permanent Army post had a telegraph office to send and receive messages which could not wait for the US Mail. The fact that it was a line key can be deduced from the presence of a shunt bar for the other side of the line and the markings on the base plate that indicate that the LINE is to be connected to one shunt terminal and one key terminal and the Relay or Main Line Sounder was to be connected to the shunt terminal and key terminal on the other side of the base plate labeled TEL for telegraph equipment.

Since the J-38 was already designed, prototyped, tested, tooled, and in production at the outbreak of WW2 it was quicker to use the J-38 for many applications than it would have been to wait for purpose made telegraph keys for individual uses to become available. As a consequence many thousands of J-38 keys were made during the early years of the war until the keys which were made for those other uses became available. When those other keys, such as the J-43 et al, became available their were already thousands of J-38 keys in the supply chain which became surplus after the war. That is why the J-38 is by far the most commonly available military surplus key.

  • $\begingroup$ Great historical perspective! $\endgroup$
    – rclocher3
    Nov 11 '19 at 14:10

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
  • $\begingroup$ In land line telegraphy a repeater is signal operated switch and a sounder is an instrument that makes clicks which are loud enough to copy the message by ear. A relay controls other receiving apparatus while a sounder is only used to copy by ear. The reason that stations had local sounders controlled by a relay was that the local sounder would take it's current from a local battery which could provide ~4-5 times the current available in the outside telegraph line. Local sounders could be louder while the relay which controlled them could be far more sensitive than a Main Line Sounder. $\endgroup$ Nov 11 '19 at 4:18

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