Saturday, August 31, 2013

The Digital Leap

I've been slowly noticing more and more my limitations of being able to get those rare DX stations attention, and noticing RFI issues. I was convinced to give digital amateur radio a shot recently, and had a good collection of notes from my efforts to go digital.

The first big question when attempting to go digital is how are you going to connect your radio to your computer. Virtually all digital communication goes through a computer of some sort, although there are two digital modes which commonly don't, CW (Morse Code), and RTTY, which often goes through dedicated machines. But all digital modes can be performed by a computer, and it doesn't take much of a computer to make it work. Historically, modems have also been used to translate from a computer to sound, but these are rarely used today.

The most common way to get the sound from your computer to your radio is via some sort of a sound card interface. These typically either work as a USB sound card of some sort. Alternatively, you can build a cable to go directly from the radio to the sound card, but then you have to either use VOX or some other method of hitting the push to talk.

Personally, I plan on using the Signalink Cable. It's inexpensive ($100), comes with ready made cables, and isolates the computer from the RF more directly than a homemade cable. Plus it takes care of the PTT issue, and my IC-735 VOX still doesn't work.

The next thing is to determine what mode you want to transmit in. There's a plethera of digital modes, I'm going to talk about the most common 3 modes, and leave the rest to your research. Typically, changing modes isn't difficult, it's just tweaking which band you hang out in, and maybe which program you run.

RTTY- This was the key digital mode, along with CW, that was used for some time. NASA used this to support it's first missions, just to give you an idea of how it could be used. It is the most common by far digital contest mode, and a good capability to have.

PSK- This is kind of like RTTY, but uses less bandwidth, and a slower transmission speed. The original variant is PSK31, where the 31 stands for the number of Hz the transmission uses.

JT65- This mode was originally intended for doing EME, it has become quite popular on digital bands. It features a 47 second receive cycle, followed by "13 seconds of terror" where your computer decodes the transmission and you select a reply, followed by your transmission, etc.

Bottom line, these all use less power and bandwidth than SSB, and have more capabilities to read in the noise. JT65 is known for working at 40 dB below the noise floor! These can be a great way to make new countries, and it sounds like a lot of fun! Can't wait to try it out!

No comments:

Post a Comment