G'Day Tony,
Depending on your distance from the TX/Rx site, and time of day, you might try a 6mhz -morning and 8mhz - afternoon for daytime use, and maybe a 3 or 4mhz for early morning & night time use.
6 and 8 seem to be good for 'most' day ranges whilst when the ionispheric 'layers' condense of a night time, the lower freqs will be best.
However, if you are oceanic, (long range) you will probably have to go to the higher freqs.
All freqs being subject to the afternoon 'Cb' interference of course....
Fairly 'general' I know, but hope this may be of use to you.
If you are able to contact your ATS provider, they may be able to provide you with an 'Ionispheric Prediction Service' for HF use for your area of operation.
These freqs are calculated from charts, and are provided for your time/area of operation. They are not 'foolproof', but are a good guide.
Cheers
