I got this article from the latest HRD Newsletter.
One of the most common requests I’m getting at hamfests lately is from prospective customers asking – “Can you show me your waterfall?” Initially, I quickly went to DM-780 and displayed its waterfall and this satisfied many inquiries.
A few months ago; however, I received a comment from a prospective customer who said, “When are you going to expand the waterfall in DM-780 to at least 25kHz?”
After that last inquiry, I started doing some research. Was it even possible to increase the waterfall in DM-780 to 25kHz?At this point, it’s important to clarify that DM-780 gets its signal from a soundcard interface that has – as its source – the AF signal from the radio. You know – that knob on the front of your radio that says something like “AF Gain.” Thinking about it – what’s happening when you turn up the AF gain? Well, you’re turning up the audio volume of the radio – just like turning up the volume on the sound system in your car. These “AF sources” are intended for the human ear. The human ear cannot hear up to 25kHz. When we’re young, we may hear up to 20kHz. As we age, the top-end range tends to decrease quite a bit.
Back when I was a telecom engineer, the bandwidth given to a voice channel was 4kHz. Why? Because that was enough for conversational speech. For AM broadcast stations (basically, double side-band), stations were allocated 10kHz (5 upper above the carrier frequency and 5 below it). Why? Because that was all that was needed for the human ear to carry on a conversation.
The point of this is – the AF range of your radio is designed for the human ear. It is “AUDIO frequency.”
For folks who want to see a display of the entire 20m band (for example), that’s 350kHz! That’s TEN times broader than the typical AF range. A soundcard is not capable of 350kHz in bandwidth. (Go read the specs for a soundcard and you’ll see what I mean.) Regardless, the AF is not giving you anything more than about 3.5kHz.
So, HOW do I get the bandwidth for this magical panadapter display? Where does the sufficiently broad signal come from? The answer is (generally) – from the radio’s IF.
Some radios bring this out to a connector on the back of the radio. Others do not. I saw a video the other day on YouTube where a guy modified an FT-857D to bring the IF to a connector on the back of the radio. He then connected it to an external SDR device and was able to display the information that comes from the SDR.
Alternatively, I’ve seen a couple inexpensive SDR radios that will give you a panadapter display. These might be worth considering. I really like the SDRplay. Another one is the RTL SDR. But do some homework. Go watch some YouTube videos about them and see if they’re for you. Also, remember that these are hardware. We’re a software company.
Let’s make a distinction. Digital modes software has held the rights to the term “waterfall” for years. It all began (in my opinion) with PSK31 and programs like Digipan. These programs displayed the contents of the AF signal in a display that everyone referred to as a “waterfall.”
The point here is – this is entirely different than displaying the contents of a panadapter. In my opinion, it’s not a waterfall. It’s a “panadapter display.” So…
When folks are looking at the waterfall in DM-780 and saying, “Oooh! You guys have a waterfall??”
Yes, DM-780 absolutely does have a waterfall. But we do not have a panadapter display. This requires hardware (generally) separate from the radio (with a caveat I’ll get to in a moment).
In the midst of writing this newsletter, I acquired an RSP1A from SDRplay. I haven’t yet connected it to the IF of a radio yet, but I did connect an antenna to it. WOW – what an impressive piece of equipment! As an SDR radio, the panadapter display with their SDRuno software is fantastic and it can display up to 10MHz of visible bandwidth! That’s impossible on the AF. If your radio doesn’t have an IF output, you have no options for a panadapter display other than modifications to the radio (like the FT-857D video). But this brought the whole topic in-focus for me. It’s about $100 for this hardware. But before you spend the money on it, go watch some YouTube videos on the topic. I hope that we will eventually have the ability to send rig control commands from software like SDRuno so that you can interact with its panadapter and change the frequency on your station rig by clicking in its waterfall. That’s an aspirational goal… but that’s what I’d like to do.
Now, back to that caveat to the “hardware required” topic…
The Icom IC-7300 is a very popular radio that has this hardware built-in. The IC-7610 also has this built-in capability. In the future, we’ll be adding software for these radios to display the data from the Icom’s radio as a panadapter display.
But as you consider your options for getting a panadapter display, I recommend the following. One – consider why you want one? What functionality do you need? And two – what hardware do you need in order to accomplish this? Is your radio already capable? What would you need to add?
73 de Mike, WA9PIE