If you want a portable antenna that you can use without adjusting an antenna coupler when changing bands then this convenient end-fed antenna may be the answer. It operates as a full sized half wavelength vertical on 14 MHz and a loaded vertical on 7 MHz. Plus it works on 10 metres as well.
The antenna is 12 metres of wire with a loading coil 10 metres from the feedpoint. At the feedpoint is a small transformer unit to step the 50 ohm transceiver impedance up to the few thousand the antenna needs. The short counterpoise can be a few metres of wire.
You can buy them commercially but it's also fairly easy to build your own. The only other item you need is an 8 or 9 metre telescopic pole to act as a mast. Watch this video to learn how to build one and the results achieved.
PS: Want to learn about other portable antennas? You'll find many ideas and projects in the top-selling Hand-carried QRP antennas.