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AE5ME > ARES 29.03.16 03:56l 9 Lines 3577 Bytes #999 (0) @ WW
BID : 144DNZU2T4KE
Read: GUEST
Subj: Digital Emergency Communications Series by AD5XJ (SAT
Path: IZ3LSV<F1OYP<F4DUR<F3KT<F1OYP<7M3TJZ<HG8LXL<N0KFQ<AE5ME
Sent: 160329/0209Z 34476@AE5ME.#NEOK.OK.USA.NOAM BPQ1.4.64
This mode can be transmitted using several modulation methods including SSB, AM, and FM. This makes it suitable for just about any band for hams where digital signals are allowed. Just as with CW, signals can be stacked very closely together without causing interference to adjacent signals. The caveat to this mode is that the rig used must have very good stability and audio quality in order to transmit and receive the phase shifted information properly. This is not usually possible with most older tube based equipment on a practical level.
PSK31 uses a Varicode 8-bit character encoding to reduce the overall amount of data that has to be sent. But no error-correction is employed so when noise or interference causes data loss. This is a severe downside to the PSK protocol in that it is not very noise tolerant and is not error-correcting as an integral part of the mode. You will notice this when conditions are noisy on the band and the computer begins to show mistakes in the text.. One possibility to slightly improve the capability of PSK31 is to use the FLMSG text format/encapsulation. In this way the text, when received will be checked with a Cyclic Redundancy Check (CRC) within FLMSG. The drawback to this method is that the entire message must be re-sent until it is received and decoded error-free. Often text only non-essential messages may be read even if the CRC fails. This mode is not generally used for image transmission such as FAX or any graphical image as a file.
Computer software programs are available now that will decode multiple PSK transmissions simultaneously in what is known as a panoramic view. The first time you see this in action it may be confusing but it is quite impressive.
Because PSK31 and the other PSK modes work well with very low power, it has gained a good reputation as being an ideal DX mode and is very popular. PSK signals can be heard in the data/CW segment of almost all amateur bands. The trend lately is to use the xx.070 region of each band. For instance on 20 meters, 14.070 is well populated. On 40 meters 7.070 is also used, and so on. The CW/data portion of all bands will find some use of PSK31. When open, 10 meters has about 100 Khz in use mostly for PSK DX contacts and CW. Often other digital modes are present and in great variety.
A very close relative of PSK is Quadrature Phase Shift Keying (QPSK). This mode also uses the phase shift scheme but only shifts 90 degrees instead of 180. This mode has gained some popularity lately due to the improvement in decoding software that includes automatic frequency control (AFC). QPSK software is now available in error correcting versions. PSKMail is also available as QPSK. This is quite a reliable and easy text mail delivery method when automated and signal strength is very good. It enjoys the same low power – high capture rate of PSK but includes the security feature of error correction at some rates.
Improvements in software have also been made that allow SOME non-text data to be transmitted in PSK. This is limited to only certain types of non-text data and the transmission time is extremely slow in comparison to other more capable modes.
The downside of QPSK is that more precise tuning and higher stability are necessary for it to be reliable in addition to the low noise and minimal QSB needs of PSK in general.
All in all, PSK is a fun and easy way to get into digital communications if you know how to type. It can be a pain if you cannot type. But have no fear there are other digital modes that do not require you to type that much.
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