Hi Astro1, here at SDRplay we are planning to add antenna information to our website. As Gary says, an active mag loop can be very effective from LF all the way through HF – some cover VHF as well. There are some good Facebook groups if you search for “Magnetic loop antennas” We recommend Bonita antennas and the Cross Country Wireless active loop antennas – see http://www.crosscountrywireless.net/ which are optimised to work with SDRplay RSPs. Right now due to Covid, they are just shipping the amplifiers and DIY materials to make your own loop. For VHF and above then a simple whip antenna will be omnidirectional and pick up quite a lot (aircraft etc) – here a good quality coax becomes more important since losses tend to be greater as you go up in frequency.
Best regards, Jon G4ABQ