Friday, December 23, 2016

Computers with Legacy Com Ports, & RTTY Interface

I was stranded an d unable to use my RTTY interface on HF, after a near lightning strike blew the 9-pin serial port on my hamshack computer. Thanks to Matt Harris KD4PBS, he had a spare plug-in card for my computer's PCI slot, to add on outboard serial ports! This provided the 9-pin legacy serial port I needed to get my RTTY hardware back working. Once I found the drivers for it, my old box was back up on RTTY.

For those of you who work digital modes, this is something to think about when you build or buy a computer... While you can use soundcard software to work most digital modes (including RTTY), it typically doesn't allow for hard-keying the FSK port of your rig for true RTTY, and often doesn't allow for hard keying your rig for CW. This means you're unable to use your narrow RTTY or CW filters (since you're usually in USB mod for all digital modes). The receiver can easily get overloaded and the waterfall gets washed out by strong stations on nearby frequencies.

There are almost no USB-to serial port dongles that support the 5-bit stream or reprogramming to 45.5 baud for this, so a USB converter is almost out of the question.

Most HF rigs have a terminal in the aux port on the back of rig for FSK control. Even my old Yaesu FT-901's have dedicated FSK and sharp receive filters for this. The majority of the digital mode interfaces that provide an output for FSK keying require a legacy serial or parallel port on the computer for this, and the majority of computers (esp laptops) have only USB ports and such, no physical 9-pin or 25-pin legacy ports. By controlling my RTTY shift through the FSK port, instead of using RTTY TX audio on USB like in DM780, I can use dedicated programs like MMTTY (love it!!) and work RTTY even in crowed contest band conditions. You might want to buy a computer that at least has an expansion port to allow for a serial port card with legacy ports for this.

Anyway, thanks again to Matthew Harris KD4PBS for the card to get my RTTY station back on the air!

Here's a pic from inside the computer, below the new add-on legacy com port card. This gave me a new com 1 & com 2 port, and disabled the old on-board port that was blown.

Another pic of the board, from inside the PC...

A pic from outside of the PC, showing the new com ports just below the ethernet card. I'm using com 2 for my RTTY interface.