Radiotelegraphy Basics: Learn How it Works

[mummyboy11]

Hi fellas,

I wonder if anyone could just gimme a glimpse of how Radiotelegraphy works (not the Encyclopedia version:zzz: ) but more like: "does it need cables?", "in what frequency are the radio signals emitted?"...cause i can't find that anywhere in the Web!

Aprecciate the help!

 

[mummyboy11]

...

 

[GENIERE]

Hi fellas,

I wonder if anyone could just gimme a glimpse of how Radiotelegraphy works (not the Encyclopedia version:zzz: ) but more like: "does it need cables?", "in what frequency are the radio signals emitted?"...cause i can't find that anywhere in the Web!

Aprecciate the help!

Jeeez! Radiotelegraphy seems to me to be an antique term, like 100+ years ago. Transmitting Morse code requires very little bandwidth so it could be done at very low or very high frequencies. I can't imagine who would be using it except possibly the ghosts of the Titanic radio operators.

 

[jtbell]

Does classic radiotelegraphy (as practiced by Marconi et al.) even use a carrier wave? I thought the "dits" and "dashes" were just broad-spectrum pulses.

[added] Aha! here's a page that discusses some of the technical aspects of early radio technology:

http://www.ieee.ca/millennium/radio/radio_differences.html

 

[rcgldr]

In order to get one of the higher ham radio licenses, you have to learn Morse code at 5 words per minute. There are several bandwidths dedicated for morse code. The lower frequences, like 10meters to 160 meters (requires huge antenna) can cover long distances since they bounce off the upper atmoshpere. As mentioned, morse code is sent as pulses (no carrier wave), but to reduce bandwidth usage, there's a ramp up and ramp down rate around 5 milli-seconds or so in the transmitters. Rather than tap out the signals manually, some use a key switch that transmits dots when pushed to one side, and dashes when pushed to the other, while programmed to a specific rate. Computers can be used to transmit and receive morse code, but a computer oriented code called RTTY is used for this purpose.

I still have an archaic "novice" license, which no longer is being issued (I just renew the old one). You needed to be able to receive morse code at 5words per minute (it was assumed you could transmit if you could receive). Technician was the next step, but still was at 5 wpm. The next two steps (general and advanced) were 13 wpm and the highest step, extra was 20 wpm. You could get casette tapes to learn morse code, but I programmed an old Atari 800 (like an Apple II, it was a 6502 based "computer") to send audio morse code with a random selection of alphanumerics. There was a group of programmers that did this at an old company I worked for. Other than the challenge of learning morse code, I didn't see the point, so I never bought a ham radio, or cb.

This is all changed now, since 2000. The morse code tests only require 5 words per minute for all classes. Obviously morse code isn't considered that important these days. There are only 3 licences, technician, general, and extra, however the old licences are grandfathered, still valid and renewable. The technician license doesn't require any morse code at all (a "no-code" license), but you get a couple more bands to use if you pass the 5wpm test, but they doen't call it a tech plus license anymore.

I'm not sure if there is any current pratical purpose for morse code, as the electronics have improved quite a bit since the 1940's. Morse code is a very slow means of communication. Most of the Ham radio morse code conversations consisted of describing their rig, and their location. They would exchange post cards to keep track of all the areas they could communicate with. One goal was to get a card from each of the 48 states, using a relatively low powered transmitter (low frequency of course).

The only other common low frequency transmissions are AM radio stations. XERB from Mexico, and KOMA from Oklahoma could be received across many states. I remember being able to receive KOMA on several car trips I made between California to Texas and back. As long as I was east of the continental divide, I could pick up KOMA. This was back in the 1970's.

 

[rcgldr]

I wonder if anyone could just gimme a glimpse of how Radiotelegraphy works (not the Encyclopedia version:zzz: ) but more like: "does it need cables?", "in what frequency are the radio signals emitted?"...cause i can't find that anywhere in the Web!

Do a web search for "ham radio morse code" and you'll find a lot of hits.

Here's a link to the official band usage in the USA (CW is morse code):

http://www.arrl.org/FandES/field/regulations/Hambands_color.pdf

and the previous page which offers a text version if you don't have adobe reader:

http://www.arrl.org/FandES/field/regulations/bands.html