[HN Gopher] Tapping Morse Code on a Wall
___________________________________________________________________
Tapping Morse Code on a Wall
Author : lightlyused
Score : 25 points
Date : 2023-06-25 12:58 UTC (10 hours ago)
(HTM) web link (mra-raycom.com)
(TXT) w3m dump (mra-raycom.com)
| crb3 wrote:
| Disagree.
|
| I'm a ham; my kids aren't... but they grew up with me using Morse
| (my computers talk to me when they boot up, and when a
| 'kitchentimer' goes off, and...) so they were naturally exposed
| to the paradigm. Maybe that's a limiting factor, but...
|
| With CW you're limited to two states: key and unkey. Knocking on
| a wall, you're not: you can go loud and soft as well. A dah has
| the same pacing as it always does (3 dits in length), but if its
| knock is perceptibly louder, at least twice as hard as a dit, in
| practice that seems to make it hold together as readable Morse,
| at least for us. Certainly our family signal, questionmark
| (..__..), is usable that way, so is each son's "call-letter".
| tnecniv wrote:
| This is off topic but I've always wanted to know what hams talk
| about on their radios (when not using it for emergency
| purposes)
| brians wrote:
| Ham radios. The weather. Space weather, because that affects
| ham radios. Growing old sucks; it's a hobby dominated by the
| aged. Antennas. Kids these days. We avoid religion and
| politics, _mostly_ , though there's an increasing segment of
| MAGA wing nuts who no longer think of their hateful rejection
| of the majority of their fellow humans as politics.
| Fortunately, one can spin the dial.
|
| It's the ARRL field day for a few more hours; check out
| http://websdr.ewi.utwente.nl:8901 near 14100 kHz, looking for
| 2.7 kHz wide voice transmissions (USB), or near 7200 kHz LSB.
| teeray wrote:
| Some communications between hams are no more than call signs,
| signal reports, and 73s ("best regards", ending the QSO
| (conversation)). This is useful for things like satellite
| communications, which are very time-limited opportunities for
| making contacts.
| lb1lf wrote:
| Anything but politics and religion, mostly.
|
| Casual small talk, antennas and other ham gear, perhaps
| trying to speak a foreign language (ham radio worked wonders
| for both my Russian and my Portuguese!), family, other
| interests...
| thrashh wrote:
| I don't know if I agree with the author's conclusion that you
| can't differentiate Morse dit and dahs tapped on a pipe.
|
| That's assuming that your listener has no brain and can't figure
| out what the longer pauses between your taps mean.
| Pinus wrote:
| I am fairly sure that I have read (probably in a 1950:s edition
| of the Swedish navy soldier's handbook "Orlogsboken"), that "tap
| morse", for example for communication with persons trapped inside
| a damaged ship, is done by tapping once for a dit, and twice in
| rapid succession for a "dah".
| Pinus wrote:
| (Page 106 in the 2003 edition, which can be found in various
| ad-infested document-showing web sites.)
| NikkiA wrote:
| It's 'inverted morse', the space length becomes the dot and dash.
| With a double/triple length space for a word break
| larelli wrote:
| The only Morse code message I know is SOS which is ...---... and
| I imagine it's reasonably easy to understand when being tapped in
| an emergency situation. It would tell rescuers that someone is
| still alive and to continue their search.
| dctoedt wrote:
| During (what we Americans call) the Vietnam War, American
| prisoners of war, often held in solitary confinement in adjacent
| cells in the Hanoi Hilton, would use the tap code extensively to
| talk to each other, sometimes carrying on long conversations, for
| example about ways to resist their captors. The article alludes
| to that but doesn't go into a lot of detail about that bit of
| history.
|
| (This is discussed in https://en.wikipedia.org/wiki/Tap_code
| cited downthread by 'dmckeon.)
| WalterBright wrote:
| If they're in adjacent cells, using a tap for dit and a scrape
| for dah should work.
| qingcharles wrote:
| I was introduced to this tap code just after being incarcerated
| and used it often. A friend and I also modified it to be able
| to communicate in/out of solitary confinement as they had
| kiosks in each cell block allowing you to order commissary
| food. The kiosks had many bugs I found in the code, but they
| especially lacked any sane range checking, so you could enter
| orders for up to 9999 noodles for instance.
|
| We broke the knock code into two "byte" pairs. So HELL would be
| an order of 2315 Beef noodles and 3131 Chicken noodles.
|
| To access the orders between cellblocks it was necessary for
| the person in solitary to write their PIN (their username was
| their jail ID#) on a piece of toilet paper and pass it to
| someone outside solitary on a day they were in court. Then both
| sender and recipient could log into the same account from
| different cellblocks and read the order. Once read the order
| would be deleted and another order placed to reply to the
| message.
|
| At first I was out of solitary, but then I got sent for
| extortion (charge dropped after 10 days, story of my life) and
| while I was in solitary the staff went through my stuff and
| found some pieces of paper where I had sat encoding and
| decoding messages. The staff didn't have the table though and
| through the FOIA I managed to get access to their working out,
| but they never successfully decoded any of the undecoded
| messages they obtained from the kiosk. After that we rotated
| the encoding table 90 degrees in our heads to act as a very
| simple form of encryption in case they tried again. It took the
| authorities another 6 months to persuade the kiosk developers
| to add a piece of code which checked the jail ID# that was
| logging in against the cellblock they were in to make sure you
| couldn't log into an account if you weren't in the right
| cellblock.
| js2 wrote:
| The argument is pedantic. It may not be Morse, but it's
| definitely possible to communicate by tapping on the wall.
| Imagine tapping out all of _Anna Karenina_ to save a fellow
| inmate 's life.
|
| https://www.npr.org/2017/09/11/550058353/rough-translation-h...
|
| https://www.bbc.co.uk/programmes/p03ttfks
|
| One of my college classes was network communications and for a
| group project, we had to devise how to transmit a binary message
| visually standing across from each other by 100 yards or so. Four
| people to a group, split two and two.
|
| The idea was to get us to strike a balance between speed of
| encoding/decoding, ability to distinguish symbols, and how many
| bits to encode in each symbol.
|
| I think my group came up with a system to transmit 3 bits at a
| time which failed spectacularly on the windy day we had for
| showing it off. My recollection is we had a big box with neon
| colored flaps that we could fold in/out.
|
| I wish we'd researched prior works of art. To this day, I have no
| idea why we didn't just learn flag semaphores. Maybe there was a
| rule against using existing systems though?
| WalterBright wrote:
| I'm confused. Semaphore is not a binary system.
| throwbadubadu wrote:
| But you could use it to encode 4 (or with the full list of
| signs and something additional) even 5 bits at once (as he
| said, they had a system of 3 already).
| js2 wrote:
| The message we had to transmit was given to us as 1's and
| 0's. But we could transmit as many bits per symbol as we
| wanted. I think we were scored based on speed and error rate,
| so it did you no good to finish first if the message was
| garbled.
|
| This was almost three decades ago and I'm working from memory
| so I may very well have some bits wrong.
| WalterBright wrote:
| Ah, that makes sense. Semaphore would have been ideal,
| then.
|
| https://en.wikipedia.org/wiki/Semaphore#/media/File:Semapho
| r...
| nickysielicki wrote:
| Anecdotally, I clicked the article, read nothing, and immediately
| listened to the first sound clip where I was able to make-out
| that it represented "CQ", but to be fair I'm a ham and "CQ" is
| by-far the most common morse code message.
|
| All you need is a ternary system where there is dit, dah, and
| silence. Even just tapping on different parts of the "wall" can
| serve this purpose, so long as it is able to be differentiated.
| Vaslo wrote:
| I have seen Shawshank probably more than 100 times and I cannot
| for the life of me remember a Morse code scene that is mentioned
| in this article.
| dmckeon wrote:
| Compare to: https://en.wikipedia.org/wiki/Tap_code
| WalterBright wrote:
| Morse SOS:
|
| bang-bang-bang---bang---bang---bang---bang-bang-bang
|
| While Morse in general has problems with just banging, with SOS
| it is not a problem.
| russianGuy83829 wrote:
| Is Morse code encoded in the lengths of the beeps or the pauses
| between the beeps?
| swalberg wrote:
| Both :) the standard unit Of time is a dit. A dah is 3 dits
| long. 1 dit between each element (so s is ... But 5 dits long
| because its on, space, on, space, on). 3 dits between letters.
| 7 dits between words.
|
| When people make the dits too long or the dahs too short (c vs
| y), or run characters together (ee or i?), it gets hard to copy
| correctly.
| myoldohiohome wrote:
| From what I remember reading, when they sent code over
| telegraph wires, dit and dah were distinguished by the time
| between clicks. Each one required two clicks to send, but the
| clicks were closer together for a dit.
|
| You could probably Google it to be sure.
| pizzafeelsright wrote:
| No, just by context. Short is shorter than long.
|
| Some cars have airbags signal the horn to SOS upon deployment.
| alexhornbake wrote:
| This is article is a pedantic waste of time.
|
| Tapping out SOS is a thing...
| https://www.smithsonianmag.com/history/the-civilian-worker-w...
___________________________________________________________________
(page generated 2023-06-25 23:02 UTC)