Posted on 02/23/2007 6:45:07 PM PST by vintage patriot
Morse code is in need of some serious SOS.
The language of dots and dashes, first used during the infancy of electronic communication in the mid-1800s, is going the way of Latin.
Beginning today, amateur or "ham" radio operators in the United States won't be tested in Morse code – also known as Continuous Wave – in order to be licensed by the federal government.
In an effort to advance the hobby, the Federal Communications Commission in December agreed to eliminate the five-words-per-minute Morse code requirement for people seeking their upper-level class licenses.
(Excerpt) Read more at ocregister.com ...
You don't have to speak more slowly. The bandwidth issue concerns how much RF spectrum is occupied by your transmitted signal. The standard narrowband SSB signal passes voice band energy in the range of 400 Hz to 2400 Hz at the -6 dB points. That's 2 KHz wide from modulation, then it is mixed to the desired carrier frequency. The only discernable effect is a "tinny" sounding voice because the high and low frequencies in a "normal" voice are filtered out.
You can read some more detail about emissions types, bandwidths and intelligibility here.
I am in agreement with you.
AS for EMP ,it affects the devices,not the operating mode.Tubes and their associated larger resistors, transformers.etc are EMP resistant because the routinely use voltages an order or two of magnitude higher than solid state units.The Russians and Communist Chineses worried a few people by continuing to use tubes in military comms years longer than the West.
Voice certainly has a higher information rate but requires the signal to be stronger. Not that it is best way to communicate,but the old timers used simple one and two tube transmitters of modest power and receivers used two or three tubes to communicate worldwide. Regenerative receivers can allow one to recieve Morse Code,AM and even SSB if carefully adjusted.
Much of the improvments of today's radios are in the ability to ignore unwanted signals and precise ,repeatable selection of the frequency(channel).Sensitivity was adequate in the HF range in the tube sets of the 1950s.Background noises of spark plugs,electric motors,non-incadescent lights,cracked powerline insulators,and thunderstorms set a lower limit on how weak a signal may be heard.
On a good quality medium, it's possible to understand speech at 300+ WPM (though many people have trouble speaking that fast intelligibly, it's possible to electronically synthesize rapid speech or speed up naturally-spoken speech). Would such rapid speech be understandable on a narrow SSB channel?
People's ability to understand speech is a function of the fidelity of reproduction, the level of ambient noise, and the rate at which it is uttered. Improving the fidelity of reproduction will increase the speed at which speech may be uttered and yet still understood by the listener.
I'm not really familiar with how SSB signals are demodulated, but my understanding is that demodulation requires that the receiver have a reference oscillator which is an extremely accurate match for the transmitter's. If the receiver's oscillator is off by 50Hz, this will cause all audio frequencies to be shifted by 50Hz. If the fundamental frequency of someone's speech is 500Hz, it will have generally have strong overtones at 1000Hz, 1500Hz, 2000Hz, and 2500Hz. A 50Hz shift would nudge things to 550Hz, 1050Hz, 1550Hz, 2050Hz, and 2550Hz. The overtones would no longer be harmonically related to the fundamental, but would instead be noticeably off.
AM reception does not have these problems. A receiver that's tuned for a frequency 50Hz above the correct one won't receive the signal as well as one that's tuned accurately, but the frequencies going into the transmitter will be accurately reproduced by the receiver.
How are CW speeds measured? If a dot is a one-unit mark followed by a one-unit space, a dash is a three-unit mark followed by a one-unit space, a letter space is an extra two units of space, and a word space is an extra four units of space, how many units per second would 60wpm be?
Certainly I would not expect a 60wpm keyer to be able to send the word "supercalifragilisticexpailidocious" once per second, but nor would I expect a 5wpm keyer to spend twelve seconds keying the word "I". For purposes of key-speed measurement, what's an average "word"? Longer than "trite" or shorter than "vox"?
That's a very high rate of speech for normal radio conversation. The extended SSB in the link I posted previously would preserve more of the high frequencies desired for better fidelity.
If the receiver's oscillator is off by 50Hz, this will cause all audio frequencies to be shifted by 50Hz. If the fundamental frequency of someone's speech is 500Hz, it will have generally have strong overtones at 1000Hz, 1500Hz, 2000Hz, and 2500Hz. A 50Hz shift would nudge things to 550Hz, 1050Hz, 1550Hz, 2050Hz, and 2550Hz. The overtones would no longer be harmonically related to the fundamental, but would instead be noticeably off.
Your understanding of the demodulation process is correct. The good news is that modern digital receivers have very stable, accurate oscillators. When I worked in the tuna seiner fleet, the standard for ship's SSB was +/- 50 Hz on over controlled crystals. Base stations are required to be correct within +/- 5 Hz. That level of accuracy produces a perfectly adequate level of understanding for common types of voice traffic between ships at sea and base stations.
You certainly can mistune an AM receiver. The front end of a superheterodyne radio must mix the off air RF down to the IF frequency. An incorrect mixing frequency doesn't shove the signal into the IF with proper alignment. The demodulation takes place after mixing down to IF. Stripping the carrier and rectifying the envelope results in passing just the upper sideband envelope to the audio amplifier after routing the carrier and lower sideband to ground. You are throwing away 2/3s of the bandwidth sent over the air. Full carrier, DSB AM is also hard on the transmitter. It must send the carrier and both sidebands. The carrier keeps the transmitter on at nearly 100% duty cycle. An SSB transmitter only puts out RF when modulation of the balanced modulator creates an output.
For testing purposes, the FCC treats 5 characters and the space that follows as a "word". Traditional amateur exams had 5 minutes of transmission at the designated speed. 5 character code groups were selected from the set that you are required to recognize. One minute of "perfect" copy was required to pass the test. People sitting for the extra class exam at 20 WPM were permitted to use a typewriter to copy. In later years, the FCC went to a "conversation" that played for 5 minutes. The "test" was a multiple choice selected from key information in the "conversation". The call signs of the parties, types of radio mentioned, location, quality of signal and type of antenna are common elements found in the test. The focus moved from perfect copy to comprehension of the important elements of the conversation.
It is a high rate of speech, but it's about what some radio ads do for their "small print". Such ads, despite their speed, are still clearly understandable.
Full carrier, DSB AM is also hard on the transmitter. It must send the carrier and both sidebands. The carrier keeps the transmitter on at nearly 100% duty cycle. An SSB transmitter only puts out RF when modulation of the balanced modulator creates an output.
I can certainly see plenty of advantages of SSB, though if all of the non-tube equipment goes kaput I'm not sure how readily stable transmitters and receivers can be built.
BTW, how do hams decide on what speed to transmit? Even if someone's capable of transmitting 60WPM it would be pointless to do so if the intended recipient of the communication couldn't decode that fast.
Though I was also wondering: I know that in the early days of telegraphy, the machines used a paper tape powered by clockwork and a electromechanically-operated pencil that would make dots and dashes. I doubt that CW would be as amenable to reliable on-off detection as electrical signalling, but I was wondering whether anyone produced strip recorders for use with radio telegraphy? Such devices, if suitably designed, might help slower coders make sense of fast transmissions (especially in cases where the transmission needed to be logged, but not acted upon instantly).
What is the balance of characters? The word "YOYO" is only four letters, but with two dots and twelve dashes would take about twice as long to transmit as "TEENS" (six dots and two dashes). Is the usage of characters in the FCC test biased in terms of letter frequency, or do all letters appear about equally?
Does this mean things like squelch controls are ineffective with SSB? If not, how would they work?
Yeah, I'm familiar with the principal of radiobeacons and radio direction finders (my job was navigation), and I have seen them on charts and in the Light Lists. I'm just saying we didn't use them in the Navy, or at least we weren't by 1982 when I came in.
FB, those are fun, stayed quite busy on SKN night and day. Used three different kind of keys for the first time. SK, Bug, Sideswiper. THe november sweepstakes is a kick, but if the condx are bad its tough to get all that info through the first time! :^)
"The November Sweepstakes (CW) and Straight Key Night are the
two I try to get in on.
Mike'
Thats great to know, I didn't realize that. I read FR frequently, nut never posted an article before.
Maybe we should post some ham articles occasionally, what do you think? That would help keep us in touch.
Also, anyone in the Orange County area Southern Cal check out our club on QRZ. KG6YSX. I actually learned CW on the air from the club.
"Many hams on FR. I wish someone would start up a ham ping list again."
"Amatuer = Amateur"
Amatuer may equal Amatuer as you say. I'm a Amatuer radio operator and there is something you evidently don't understand. There is a world out there on the radio waves that you wouldn't even know is there if you aren't a operator or a listener. Turn your TV off and turn on a radio that is capable of recieving Medium Wave, AM with upper and lower side bands. You will find a world that you don't even know exists.
kb2zlz
I know.
I hope get a chance to wave a hand at you soon kb2zlz, 73 from kd8adm.
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