Perhaps the easiest antenna for emergency communications on Shortwave is a simple wire connected straight to the radio.
This works adequately for reception, but for transmitting requires a matching unit and choice of a correct length of wire to match the transmitted frequency.
All important is the matching unit ( it will make reception better too). These are now readily available on the usual trading websites.
I use this one, which has a handy reminder of wire length needed and doubles up as an spool for the antenna wire itself.
These can be had for as little as £10.00.
See
https://www.ebay.co.uk/itm/Portable-No-T...Sws3RfkVNH