What bands can be used during contests?
That depends on the particular contest. Some contests are limited so a single band – for example, the ARRL 10m contest is (not surprisingly) for 10m only. Many contests allow operation on all the pre-WARC HF bands – that is: 160m, 80m, 40m, 20m, 15m and 10m. Other contests are for VHF bands only. However note that contesting is never permitted on the WARC bands: 30m, 17m and 12m. This is so that amateurs who do not enjoy contesting can take refuge on the WARC bands during contests.