Bandwidth Comparison
Because it has 64 tones, the MT63 transmission is quite wide (usually 1 kHz), and it has a harsh rushing sound. It has sharply defined edges, so it is possible to fit two MT63 transmissions in the width of an SSB transmission. Yes, MT63 is still less than half the bandwidth of an SSB transmission.
Bandwidth Comparison
MT63 may seem rather wide for a digital transmission, but bear in mind that it offers 100 WPM performance, and is no wider than a 75 baud 850 shift RTTY signal, or twice as wide as a 45 baud 170 shift RTTY signal (yes, OK, or 20 PSK31 signals). While wider than HF packet (300 baud, 500 Hz), it offers better throughput under most conditions. Packet and most other ARQ modes only give their maximum throughput under ideal conditions.
Bandwidth ComparisonNote - PACTOR 2™ and PACTOR 3™ are considered non-Amateur modes and are not compared.
The throughput of ARQ modes deteriorates markedly under less than perfect conditions, whereas FEC modes "hang in" and drop out suddenly.There is invariably some dispute about how well ARQ modes perform under poor conditions. The following table attempts to compare throughput under good and poor conditions found from practical experience. Voice SSB is shown as a reference.Throughput Comparisons
Mode Bandwidth Hz WPM (Good) WPM (Poor) MT63 1K 1000 100 100 MT63 2K 2000 200 200 PSK31 60 50 50 HF Packet 500 200 0 Amtor ARQ 300 50 0 - 1 Pactor 300 200 0 - 10 Clover 500 200 0 - 10 75/850 RTTY 1200 100 0 45/170 RTTY 300 60 0 Voice SSB 2400 250 5-10
Latency is a measure of the time taken for transmitted data to pass through the transmission and reception equipment. As a simple example, it takes 165ms to transmit a 45 baud RTTY character via a UART, and the same to receive it - a total Latency of 330ms. Compared with this, the propagation delay half-way around the world (65 ms) and the delay through the transmitter and receiver filters (perhaps 10ms) are small.In a way, Latency is a measure of the "slick-ness" of a radio mode, since it strongly affects the turn-around time, which is the time from the last transmitted character being sent from the keyboard, to the time the first character in the return direction appears on the screen. The turn-around time is at least twice the Latency, since the return process cannot start until the last character has been received. Other factors such as propagation delays, key-up time and any preamble that is to be transmitted must be added as well.
The following table gives Latency estimates for MT63 andsome common HF (non-ARQ) modes.
Latency Comparisons
Mode Version Latency (sec) MT63 500Hz short 12.8 MT63 500Hz long 25.6 MT63 1K short 6.4 MT63 1K long 12.8 MT63 2K short 3.2 MT63 2K long 6.4 PSK31 - <1 MFSK16 - 6 Amtor FEC - <1 45 baud RTTY - <1 It is obvious that MT63 is not very "slick". The "turn-around time" in MT63 1K with short interleave is at least 12.8 seconds! In addition, if conditions are especially poor, it can take the MT63 receiver a significant time to acquire lock, so the figures in the table are optimistic.
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