The WSJT-X program is very robust and reliable. It decodes multiple signals at once, and is very good even for overlapping signals. WSJT-X includes multiple high performance digital modes for LF, MF, HF, VHF through microwave, each tuned for challenging propagation conditions.
2600 Hz is a typical frequency boundary between JT65 (below 2600 Hz) and JT9 (above 2600 Hz). Some people use +/- 100 Hz from this.
Control transmitter RF output power with the sound card output level, NOT with radio RF power control. Optimize transmitter cleanliness by:
- set the RF power control to well above the intended transmit power level (say 6 dB to 10 dB higher)
- set microphone gain to about midrange
- set computer audio volume to precisely set output RF transmit power
If the radio transmitter is driven into ALC by using RF power control to limit transmitter level, the radio will splatter, interfering with adjacent frequencies. This happens with any digital mode.. Most people use 1 to 5 Watts transmit power for WSJT-X supported modes. Some use a very minimal amount of RF power for a “kilometers per watt” challenge.
Older radios often have too-narrow receive filters to capture the whole JT* band of frequencies. These filters do not have infinitely steep skirts, but you will certainly take an SNR penalty outside the passband. Most stations operate at no less than 300-400 Hz above carrier frequency. If the radio has “IF shift” or “pass band tuning”, it might receiver from 400-2800 Hz, with ability to hear stronger 3000 Hz JT9 stations. It’s a tradeoff between missing stations on the edge of either band. JT65 DX sometimes squeezes as low as 300 Hz, typically accomplished by their radio using Split TX frequency. I have also see JT9 as high as 3500 Hz and beyond.
A radio that receives on multiple HF bands simultaneously greatly increases the data gathering capability for ionospheric studies. SDRs oriented toward “traditional” ham radio use typically receive one or two RF bands at once. Simultaneous multi-band reception can be accomplished with a bank of SDR receivers or a broadband SDR like Red Pitaya.