Consult your owner's manual for more information on how to do this. If you ever hear a station at two or more frequencies at the same time, the cause is almost always overdriving. None of this applies to FSK, of course.
With FSK, you can run full power and not worry about overdrive. RTTY uses the Baudot code, invented before radio even existed, and still widely used throughout the world. The Baudot code uses data bits to represent letters, numbers and punctuation, much like your computer does. Unlike your computer, which uses eight bits for each character, the Baudot code uses only five, plus a start bit and stop bit. Using fewer bits is good because it speeds up transmission and reduces the chance of errors, but there is a complication.
Five data bits can only represent 32 different characters. Since there are 26 letters in the English alphabet plus ten numbers, plus some punctuation, 32 different characters is not enough, even if you only use capital letters, which Baudot does.
Baudot could have chosen to use six data bits or even more, but he found a better solution. He reasoned that most of what would be sent would be letters rather than numbers or punctuation, so he assigned all the letters to the basic He then had six characters left over and he did a very clever thing with two of them.
The way it works is this: When sending one of the basic 32 characters, nothing special happens. Whatever follows will still be one of the basic 32 characters, but the receiver will interpret it differently. It's all automatic and you will scarcely notice it happening. In fact, the only reason to mention it at all is because we are using radio instead of wires, and radio is susceptible to interference from various sources such as lightning static, man-made noise, etc.
Instead of printing , the other fellow's computer will print TOO. We all got used to interpolating "shift" transmitted reports and serial numbers in the early days! With the right mouse button, just click on the word and it is instantly changed to the opposite shift. Right-click again, and it's shifted back. Easy as can be. When the bands are nearly empty, you can use practically any receiver bandwidth with good success. Your SSB filters are probably between 2.
For optimum performance however, less bandwidth is better, in fact MUCH better. If you don't have a Hz filter, Hz will do pretty well, but anything wider than that will not be satisfactory in the long run.
Further discussion on this subject can be found elsewhere. For amateurs, the ARRL handbook is a good source. Depending on your transceiver, you may or may not be able to use a narrow filter for RTTY. Some of the less expensive transceivers do not have an FSK mode, and also are unable to select a narrow filter while in the LSB mode. Using an outboard audio filter between the speaker output and the soundcard input can make some improvement, but unfortunately, that will not prevent a strong adjacent signal from causing the receiver's AGC circuit to reduce gain, often to the point where the desired signal disappears.
The best solution is to upgrade to a transceiver that has an FSK mode built in, AND which allows you to select a narrow filter while in that mode. It's easy to remember the band plans for RTTY. Most activity will be found between 80 and kHz up from the bottom edge of the band, except for 80 meters, which goes an additional 40 or 50 kHz higher, and meters.
Avoid the CW DX window between - At present, there is not much activity on the WARC bands, although 30 meters can be active at times. Here is where you will find most of the RTTY activity: 80 meters: - - in Japan 40 meters: - in the US see note below 30 meters: to top of band 20 meters: - avoid the beacons at 15 meters: - 10 meters: - RTTY allocations for 40 meters vary greatly all over the world.
DX activity is often found between and About time we had another kHz of allocation on this band. Check your BR68 for the UK allocations. Just like with CW or phone, if the DX is calling CQ and getting no answers, you can feel safe in calling him right on his frequency. If things are busy however, he will often work split, which means you should call him on a different frequency, usually kHz higher.
He will say "up " or something similar at the end of his transmission, and that's your clue. Either way is acceptable. Most modern transceivers today have an FSK input. I am biased in my opinion of AFSK vs. There are advantages and disadvantages to both. If the audio is too high it will overdrive your transmitter and more than likely result in a distorted RF signal or cause your radio to put out "image" signals across the band.
This will also cause problems on your RF signal. The only real advantages to running AFSK are that you can get started rather quickly using this method because it's simple audio-to-a-soundcard input for receive and audio-from-a-soundcard output to your transceiver for transmit and you can also make use of the NET features of sound card programs.
But personally, I think NET is a nice feature, but it can cause problems when not used correctly. Check your manual to see if this is the case for your radio. I don't have to worry about the audio level or whether I forgot to turn the speech processor off. I can then use the FSK mode on my radio along with the narrow and hz filters.
There is a little more work involved when using FSK. That would not be good. One of the drawbacks of RTTY is the limited set of characters that can be sent - only text and numbers, and very few other characters. When using RTTY, the data is sent relatively slowly because the mechanical teleprinters could not cope with data any faster and the standard has remained in place to retain compatibility with existing equipment despite improvements in current technology.
The RTTY frequency shift between the two tones used to be standardised on Hz but this is often increased to Hz as a result of the many of the new digital modes. As the difference between the two standards is relatively small there is no incompatibility between them. Typically the Hz difference is generated using audio frequencies of Hz to represent a mark condition and Hz to give a space.
One of the advantages of RTTY having a low data rate is that it means the bandwidth required for the transmission is relatively low. It is easy to gain a rough estimate of the bandwidth required by doubling the baud rate and adding the frequency shift. For example, a 50 baud transmission using a Hz frequency shift would require a bandwidth of Hz, so a Hz filter would be quite acceptable. By using a narrow filter, the effects of interference can be minimised. In view of the relatively narrow bandwidths and the need to be able to tune in the tones to approximately the required frequency, a receiver or transceiver with a reasonably slow tuning rate is needed.
Typically it should be possible to tune to within about 50Hz. One of the major problems with RTTY is that any interference causes the received data to be corrupted.
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