Saturday, July 3, 2010

I want to put together a computer for my station, but it is a frustrating process ...

Q Jim, KM4GU, asks, “I want to put together a computer for my station, but it is a frustrating process. Many of the computer retailers sell ‘custom’ PCs that they will assemble to your specifications, but when I talk to them about my ham requirements, they are utterly clueless. This is particularly true when it comes to the number of COM ports that I need. Can you give me some advice?”

A The problem with buying a computer for other than traditional applications is that there are usually only 16 IRQs, 2 COM (serial) ports, one printer (parallel) port and a finite number of card slots on the motherboard. There is nothing that can be easily done about the IRQs or the number of slots.

The IRQs (Interrupt ReQuest) are channels that exist for devices to tell the microprocessor that it needs some processing time to perform a task—to recognize that you have pressed the keyboard, printed a document, put something on the screen, used the telephone, updated the clock, and on, and on, and on. About half of the IRQs are used for the bare bones computer to run itself. The rest are for you to do with as you wish…almost.

The company that is putting your computer together for you also has some favorite IRQ robbing devices that they believe you can’t live without. The average “we can build one for you” computer has two IRQs still available when you get it. Believe it or not, the first Dell 500 MHz, Pentium III, multimedia, CD-ROM burning, DVD, mouth-watering, machine on the market had zero IRQs left for other applications!

Another confusion factor is that IRQs can be shared if the sharing devices are “friendly.” Divining which IRQs can be shared is voodoo magic. Windows 98 gives it the old college try, but it’s not perfect. Sharing is also possible for COM and printer ports.

COM ports are somewhat easier to deal with. Most computers today come with a PS2 mouse so COM 1 is left free. This often leaves COMs 1 and 2 for you to use. There are also cards available that will supply you with four COM ports, provided you have a motherboard card slot free. Are you starting to get the picture? So, before you visit the dealer, you need to determine the number of COM ports, IRQs and card slots you are going to need for your ham applications in the foreseeable future. When you show up at the store be sure to ask, “After all the components and software are installed, how many IRQs, COM ports and card slots do I have left for myself?” Let their answers to that question, and your budget, guide your choice.

If you feel up to the challenge, consider assembling your own shack PC from components you purchase yourself, either on line or from a local outlet. You can throw together a bare-bones PC that will leave you with five or more IRQs, three or four card slots, and both COM ports free. A capable ham computer with a 333-MHz Pentium II microprocessor, a 1 Gbyte hard drive, a CD-ROM, basic modem, sound and video cards and a mouse can be slapped together for about $500. Perfectly serviceable used monitors can be had for about $100; new, just a little more. Take a look at the Pricewatch site on the Web at http://www and you’ll find a huge collection of component and system bargains.

Keep in mind that for most Amateur Radio applications, processor speed, hard drive speed/capacity and whiz-bang technologies are not necessary. Even something as “primitive” as a 486- DX66 machine will be fine. You can pick up one of those PCs for as little as $100 used.

From QST August 1999