What HF frequency is best?

Typically this can be 3.5 – 3.8 MHz , although in North America, frequencies up to 4.0 MHz can be used, although there is a broadcast band allocation above 3.8 MHz. This ham radio band can be quite noisy, especially at night as it is shared with other services and this can make it very busy.

HF users have found that using a frequency that is the MUF times 0.85 gives the best chance for good results. This is called the frequency of optimum transmission (FOT).

High-frequency (HF) radio is in the 100- to 10-metre wavelength band, extending from 3 megahertz to 30 megahertz . Much of the HF band is allocated to mobile and fixed voice communication services requiring transmission bandwidths of less than 12 kilohertz.