One of the things you will get to learn through Amateur Radio is the calculation for making antennas.
Speed (in metres) divided by Frequency (in Megahertz) divided by the part of antenna length of interest.
So, 300 / 978 / 4 (for 1/4 wave at 978 MHz for UAT) = 0.07668 (which is 76.68 millimetres) so cutting at 76mm will be just fine.
All the Amateur bands are often known by their (approximate full wave) metric antenna length i.e. 80 metres, 40 metres, 20 metres … 2 metres, 70 centimetres…
Buy another dongle plus an HF upconverter (Noolelec ‘ham-it-up’ or similar) hook up some random longish length of wire to the centre pin of the coax connector, throw the wire out of the window, install SDR# (SDR Sharp) and tune around 7.05MHz and 14.1MHz and 21.2MHz etc and listen to what you can hear from around the world.
You will find that morse code is still very much alive and was perhaps the first mode of digital communication and the first ‘social media’ !
I have been a ‘ham’ (in the UK) for over 30 years and still enjoy every facet of the varied hobby and wish you well on your ham journey.