ding software, some free, others not. there are new modes being invented all the time and keeping track of these is turning into a full time job! one of the main problems encountered by the newcomer to digital modes (or digimodes as they are known) is how to identify what they are seeing/hearing. most of the decoding software uses a visual ‘waterfall’ display to facilitate easy tuning.
with that in mind i went on the bands and captured images of the most common digital modes in use at the moment. below you will see images of each mode together with some brief notes on the mode. the images show the most common variant(s) of the mode, although some have many different ‘flavours’! i will add to this list as and when i hear/identify a new mode that is being used on a regular basis (last popular ‘new’ one is olivia which wasn’t around when i did this page on my original site)
click on the name of the mode (where the name is underlined) to hear an mp3 of how the mode sounds on air.
psk31
because psk31 has a bandwidth of only 31hz, many signals can fit into the same bandwidth that would be occupied by an ssb signal (2.4khz approx.). it is quite common to see 15 or more signals on a 2.5khz waterfall display.
a ‘clean’ bpsk31 signal. this is how your signal should look!
a bpsk31 signal that is badly distorted. this is probably due to overdriving. reducing the input to the soundcard or reducing the output level would improve the quality of this signal. note that although some way from the adjacent signal on the left, the distorted signal is sufficiently wide to cause interference to the other signal.
here we see a station that has an unstable signal and is drifting badly. a stable and ‘clean’ transmitter is vital when using narrow modes such as psk31 and it’s variants so as not to cause qrm to nearby stations
psk63
psk63 is gaining popularity, with many programs now supporting this mode. the pro’s for this mode are the fact that data is sent and received at twice the rate of normal psk31, so is great for chatting and contest exchanges. the con’s to this mode are the increased bandwidth required over psk31, the increase in power required to maintain the same level of copy as psk31 and that not all software decoders support psk63. psk63 can be identified quite easily as it looks like a ’fat’ psk31 signal!
other variations of psk31 are psk16 (half bandwidth/speed of psk31); psk125 (4 times bandwidth/speed) and other experimental variations. the other common variant of bpsk31 is qpsk31, which is sideband dependant (i.e. both transmitter and receiver must be using the same sideband) but is not in common use despite it’s superior decoding ability during poor conditions.
sstv (slow scan tv)
slow scan tv has been popular for many years, although the vast majority these days is computer generated. the most common modes are martin and scottie. robot still has a following. most sstv programs handle these modes and others too. the received pictures are built up line by line over the course of nearly a minute so you need to be patient! quality can be very good, even over long distance paths. here are two pictures received by me — the left one is from hawaii (kh6at) and the right one is from sweden (sm7uzb).
rtty (radio teletype)
the ‘original’ data mode. rtty (pronounced ‘ritty’) has been around for many, many years and is still just as popular. years ago the only way to get on rtty was to use a mechanical terminal unit such as the creed 7 series, which were big, noisy and messy. these days, virtually all rtty is done by the computer/soundcard combination. amateurs (hams) use 45 baud (the speed) with 170hz shift (between mark and space). commercial stations use 50 or 100 baud with shifts of 425 or even 850hz. most software caters for differing speeds and shifts. unlike most digital modes, rtty is transmitted on lsb.
mfsk
mfsk is similar to the commercial piccolo system. mfsk is very good under poor propagation conditions. the usual variant of mfsk is mfsk 16, but other types such as mfsk 8 are in development, along with other similar modes to mfsk (such as domino). mfsk is sideband dependant, so you must have your receiver set to the correct sideband in order to decode it properly. also tuning is quite critical, although afc helps somewhat.
mt63
mt63 is very robust and offers 100% copy when other modes fail. the tradeoffs however are bandwidth and speed. mt63 is quite slow and occupies anything from 500hz to a full 2khz (which is still less than a single voice channel). because of the wide bandwidth, mt63 is usually confined to 14mhz and above, where there is sufficient space to accommodate it.
