Friday, August 2, 2013

The Elecraft K3 is a Joy on RTTY

K3 - Right in the operating position
I built the K3 just after Christmas. Since then, it has been a joy to operate in many ways. Having just completed my third RTTY contest this year, I'm especially pleased with how it operates on RTTY.

Although I operated packet radio back in the 1980s, I never got a make a RTTY contact until 2005 - using my Elecraft K2. I built an audio interface using a couple of audio transformers and some resistors.

In many ways, the K2 is a great radio. Gary Breed K9AY told me that the K2 was, "a simple radio, superbly executed." While I do enjoy the K2, it is not at it's best running RTTY or any other digital mode. It suffers several limitations:
  • Duty Cycle - The K2 is designed for a 50% or less duty cycle - CW or SSB. Without supplemental cooling, you can't run the K2/100 much more than about 25-30 watts. I added a small fan on top of my K2, and could safely run 50-75 watts of RTTY without overheating. The K3, of course, is a 100% duty cycle rig - no problem running 100 watts for hours. The case doesn't even get warm.
  • Tuning Rate - Because of it's design, the K2 tunes in roughly 9 Hz steps. While the display shows the nearest 10 Hz at all times, the firmware selects the closest tuning point. As you turn the dial, it's not entirely smooth, sometimes jumping twice as far. With the finicky tuning of RTTY signals, you'll notice this.
  • Frequency Readout - I put this one in my K2 Wish List. The K2 frequency doesn't account for the mark frequency, and thus reads 1-2 kHz high, depending on what audio tones you are using. While some contest software can compensate for this, the K3 works correctly by showing the mark frequency on the display.
  • Variable Transmitter Gain per Band - this is the most annoying thing about using the K2 on RTTY. Because of the way the K2 transmitter gain control system works, you have to adjust your audio levels on each band -- very high levels on the higher frequencies, and extremely low levels on the lower bands. Every time you change bands, you must adjust the transmit audio level. Every time. The K3, on the other hand, calibrates itself so that it has the same gain on every band. 
But the best part isn't that the K3 can run flat out 100 watts, tune smoothly, display the right frequency, or make it so you don't have to mess with the transmit audio level in the middle of the contest. These other features of the K3 really enhance RTTY operation:
  • Variable-Bandwidth IF - My K2 is programmed with a variety of bandwidths for RTTY: 1000 Hz, 500 Hz, and 300 Hz. But this isn't nearly as convenient as being able to select any bandwidth from 100-4000 Hz. On a quiet band, a bandwidth from 600-800 Hz works well. When the QRM gets tough, pulling down to 300 Hz puts it in its place. The K3 allows you to pick exactly the right bandwidth for the situation.
  • Dual Passband - RTTY contests can get downright ugly. Sometimes strong stations are interlaced on top of one another, so the mark or space frequency of one station is right between the tones of another station. This situation does no good for anyone, as it makes it nearly impossible to copy either station. I'm convinced that this is largely due to the over-use of  dual passband filtering. This type of filter puts a huge notch between the mark and space tones. It's not useful for S & P work, because if you are slightly off frequency, you won't hear stations. And, it's not terribly useful for calling CQ, either, since someone can easily move in between your tones and you won't hear them. However, every once in a while, this filter makes the difference between completing a QSO and losing one to the QRM. Just don't use it all the time, OK?
  • Fine Tuning - While the K3 tunes in perfect 10 Hz steps, you can select fine tuning mode with 1 Hz steps. I used this all the time as default for CW and RTTY and move it. It makes tuning across the band take longer, but it's easy enough to switch to 10 Hz steps when you need to.
So, every time I changed bands, tweaked out QRM with the filter or passband tuning, marveling at how cool the rig is running pumping out 100 watts hour after hour or just simply tuned stations in -- I'm consumed with joy over this fine radio. Definitely worth it.

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