Last time, we took a look at cables and connections required to hook-up a computer, a TNC, and a transceiver in order to "go digital". It is now time to look at switching arrangements that allow using the same transceiver for both digital and voice. While we’re at it, let’s look at other switching that may come in handy.

I must point out that, with some transceivers, YOU MAY NOT NEED VOICE / DIGITAL SWITCHING AT ALL. Be sure to check-out the equipment you have, or plan to get, to determine what type of switching you need, if any. Obviously, there is no need to build an elaborate switching arrangement if your equipment already does it for you. One of the rigs I am currently using, for example, has a "data" mode (in addition to USB, LSB, CW, and AM) and a jack on the back panel to accept a cable from the TNC. Most modern rigs have similar arrangements.

The switching you will need depends on, among other things, your personal operating habits and the type of equipment you use. For example, if you never use CW, you obviously need not bother with switching between manual and computer keying. If, on the other hand, you are a CW fan and do lots of contesting, you will want to be able to switch between casual and contest keying. If you use a contest logging/keyer program (as I do), you will want to be able to take advantage of the automatic keying it provides. Even if you need no external switch-box with your equipment, the switching must (somehow) take place, and you may find it interesting to "sing along" while we explore the process. 

As shown last time, your TNC will require at least the following lines: audio in, audio out, push to talk (PTT) and ground. Ground, of course, is never switched, it is (or should be) solidly connected at all times to every box in your station. It is amazing how many problems, both intermittent and solid, can be traced to inadequate or improper grounding, but that is a subject for another day. 

Your switching arrangement may look something like Figure 1.

If you do not use CW at all, or if you are a casual CW operator and plan to use only the keyboard keying provided by your TNC, you can eliminate the "A - Computer CW Key Line" and the "Key or Paddle".

Assuming you need a full-blown switching arrangement, let’s take it one-step-at-a-time, starting with voice/digital switching, shown in Figure 2. The switches can be any type you like, rotary, lever, toggle, or relays. I use (mostly) salvaged switches from TV sets and audio equipment. If you are buying new switches, I recommend rotary switches because they are relatively cheap and easy to find.

For the hard-core CW enthusiasts, additional switching will be required. Worst case (or best case, depending on how you look at it) you will need switching for the following lines:
 

• Paddle Dit line in/out
• Paddle Dah line in/out
• CW Key line to transceiver 
• T/R control and/or Push to Talk (PTT)

An example of CW switching is shown in Figure 3. The example shown assumes your transceiver has a built-in keyer, and that you are using a computer logger/keyer program. This means you would NOT be using the TNC and Keyboard for keying. Additional switching is required if you use an external keyer, but the fundamental idea is the same. A simple DPDT toggle switch can be used for this switching.
 

If you have never used a full-function logger/keyer program, the "Dit to ‘Puter" and "Dah to ‘Puter" lines are probably new to you. Basically, what happens is that your computer becomes your keyer (with TONS of memory for messages, etc.) so you must connect the paddle to the computer. With the logger/keyer program I am currently using, the paddle lines go to the parallel port, Dit line to Pin 12 and Dah line to Pin 13. The CW Key line comes out of Pin 17. Logger/keyer programs are really neat, and a whole article could easily be devoted to explaining all the things they do, bit I'll save that for another time. 

This switching may look complex at first glance, but if you take it one line at a time it is quite simple. Then, you combine all the switches in your switch box, and you’re done.

Next time, we’ll take a look at peanut butter jars, and their many uses in electronics, from the mundane to the exotic. Peanut butter jars?? Yes! Stay tuned …

73, Dick, W6BKY