These words are often used interchangeably. Without getting into the semantics of the differences, the point here is… everybody wants a broadband view of the RF spectrum. Let’s call this a “panadapter display.”
What is conceptually hard for most folks to understand is this – no software can create a panadapter display from a radio that isn’t capable of producing one.
Let’s go back in time. It wouldn’t surprise any of us that our old Heathkit, Drake, Collins, and Hallicrafters gear couldn’t produce a panadapter display. We all know that none of these had any method for computer control.
When soundcard-based digital modes became popular, most of these programs displayed signals in a “waterfall.” These waterfalls – still used today – are limited by two factors.
Soundcards have a bandwidth of about 20 kHz. This is roughly the bandwidth that the human ear can hear. That’s almost enough room for 6 SSB signals. That falls well short of the full bandwidth of a ham band. But the bandwidth of the soundcard isn’t the limiting factor. By comparison, commercial FM radio stations are given 16 kHz of bandwidth. That’s one station.
The limiting factor is the AF bandwidth of ham radio receivers. Using the new Yaesu FTdx101D/MP as an example, the audio frequency bandwidth is 2.4 kHz on SSB.
To net this out – if you connect a soundcard with 20 kHz bandwidth to the audio output of a typical ham transceiver that has 2.4 kHz of bandwidth, your “waterfall” is limited to 2.4 kHz. The 20m band is 450 kHz wide. So it’s not possible to create a panadapter display from the audio output of a typical ham transceiver.
Some transceivers have a display that looks like a panadapter display. Some of these transceivers have the ability to display it on an external screen. Software can only produce a panadapter display if the transceiver can produce data via its CAT commands or via IQ data. This is a very short list of radios made in the last 5 years or so - iCOM IC-705, IC-7300, IC-7850/51, IC-7610, IC-9700, Kenwood TS-890S, and any Flex Radio. As of the time this is being written (20 Feb 2022), no other radios have the ability to generate the required data to create a panadapter display.
So what can you do if you have a radio that isn’t capable of producing the data that software needs to create a panadapter display? You get an external panadapter like the SDRplay. You can connect it either to the IF output of the radio, or use an antenna splitter (like the MFJ 1708B-SDR). This provides the RF signal that the external SDR radio needs to produce the panadapter display in software. The SDRplay comes with software called SDRuno.
There are lots of videos on YouTube that demonstrate how to connect the SDRplay to radios with - or without - the antenna splitter. You would choose the method that fits your circumstances.