[No run since Wednesday, two days of tower climbing work Friday and Saturday]
I’ve been working on my DDS thing, and I’ve done this before. I got to a certain spot and set it aside because I didn’t know where to go next. But now I’m back and I have an end goal: adding RIT to my SS-40 QRP radio so that I can use it for the 40 Meter fox hunt. And I am doing that by replacing the analog VFO with a DDS.
I’m spending some time thinking about radio user interfaces.
Let’s imagine a situation where someone hands you a “control” and tells you to “move the zingle to 12 by snoggling this gizmo-whitz.” So you take the thing in your hand and you see it has a little indicator showing a 3 digit number now saying “73.2” and four buttons labelled with arrows. What do you do?
Now imagine the indicator is a horizontal ruler dial with labels on marks incremented in 5’s from 0 on the left to 100 on the right. There is a red colored vertical needle sitting slightly above 35. And again there are four arrow buttons. What do you do?
How about when the display is a digital number but the control is a knob? Do you turn the knob left, or right? What does “left” or “right” even mean when you are twisting a round thing??
I was in the shower and thinking about these things. I came up with a couple of pragmas:
Pragma #1: The expected effect of a wheel control is by the relative motion of the “top” of the wheel.
Driving a car, you turn the wheel “right” to go rightward. The top of the wheel actually does go rightward. [On a zero-turn mower (or a tank) you push the stick forward on the side you want to go faster. On a motorcycle you lean toward the direction want to go (pushing harder on the handlebar in an exact option motion as the zero-turn/tank thing). You actually kind of fall and the motorcycle catches you and you turn… it’s a lot of fun! Back to radios]
The little radio I’m working on was originally equipped with a knob and no indicator at all. The knob does not make one full revolution; speaking in clock-face, it goes from approximately 8 to 4 in an imaginary arch with stops at each end. The rightward end (“4”) is minimum frequency and the leftward end (“8”) is maximum frequency. [Can you tell I am already lost in the weeds trying to explain this to you? With sensory feedback it really isn’t difficult.]
I have another radio, the Drake 2B receiver, with a big rule-dial and a vertical red-line indicator. 
It has two controls for determining frequency: band switch and big knob. The band switch selects what band and the big knob moves the red line left and right. [The movement of the top of the knob corresponds to the left-right of the red line!] One tricky thing is the dial shows frequency increasing left-to-right on some bands and right-to-left on other bands. All of the bands going one way are above the ruled line and the all of the bands going the other way are below the line.
The band switch is a “jump” control. You can imagine a very long dial from 3.5 to 28.5 and a big knob and you turn the knob round and round and round and round moving the red line all the way, yards and feet and inches.. .to get from one end to the other. The radio doesn’t actually work in the intervening frequencies, only in these little “windows” into the whole range of possibilities. So the band switch jumps you to a section of the whole spectrum.
Definition 1: Moving a knob to get from one frequency to another is driving.
You start at the current spot and you go “up” or “down” from there in a relative sense until you get to where you want to be. You may be looking for a specific number, or listening for a signal or otherwise getting feedback that lets you know when you get there.
Definition 2: The band switch is more like flying: you plop into another range of operation, like flying into the airport from which you then have to do driving to make localized changes.
When digital displays enter the picture you have a third form of interaction arise: direct number entry. With a calculator, keyboard or phone keypad you just “punch in” the numbers.
Direct entry doesn’t work so well in physical systems. Imagine if the speed control of your car was direct entry. You want to go 45 MPH so you punch in a 4 and you lurch out at 4 MPH. Then you hit the 5 and suddenly you are going 45! Then you want to increase to 51 so you hit the “5” again and… do you go 5 MPH or 455 MPH? Wait! you say, We need an “enter” key. Good idea: punch in 45, hit enter. Punch in 51, hit enter. School zone, punch in 25<enter>… wait, there’s a red ball rolling into the street… slow down! 20<enter>10<enter>5<enter>…. [or 0<enter> screeeetch!]
Direct entry is more like flying than driving: you punch in 20<enter> and it instantly transports you from where you are to where you want to be – <zip!>
So, we have controls for driving or flying and we have feedback. The feedback in a radio is visual and aural. If someone says, “meet me at 7030 kHz” I punch it in or turn the knob or do whatever is necessary to get to the indicated position (either digital or analog dial). But usually my indicator isn’t exactly the same as yours so I need to fudge it a bit: when we start communicating I can hear you but your signal sounds funny or weak so I want to drive around just a little as a local adjustment. In the old-television days we called that “fine tuning.”
Sometimes it is all aural like my little QRP radio which has no visual indicator at all. I just turn the knob and listen for signals. I hear one, I adjust to make it sound good and that is all. I am happy with that until I go to record our frequency in my log book and all I know is that we were somewhere between min and max. Or if you tell me to “meet me at X” and I spend a lot of time searching up and down, up and down, not knowing where X is, not so happy.
For the fox hunt, I want some of each. I have a range of frequencies between which the fox is operating, and I can hear fainter signals by tuning across them. This is morse code, so each signal is a little eeeeee. As you tune the note of the beep goes up or down. The change in note makes a faint signal stand out from the shush of the noise that is always in background. Radio guys say that a faint signal is “in the weeds”. There is always a lot of signal but most of it is continuous shushshshshshshsh. You tune through and you hear shshshshshshsheeeeeooooohohohsshshshshshshshsh And you had yourself a signal there. So I want mostly driving but a little bit of feedback about where I’m driving.
That’s enough for now: Next part – Driving Speed