Pete Meier WK8S
We’ve had computers built into many of our radios for some time that control various features. However, with the adventurous release of Ten-Tec’s Rebel you now can control and change what and how that computer performs it’s duties.
The Rebel 506 is CW transceiver incorporating an Arduino-based microprocessor. It’s Open Source for both hardware and software – meaning that nothing inside is proprietary and the owner/user is encouraged to experiment and innovate. Hams have always enjoyed “hacking” and sometimes improving their radios. The Rebel invites you to truly make it your own right down to the software that runs it.
The Rebel is a inexpensive,and interesting Qrp CW transceiver right out of the box with DDS VFO coverage of the 20 and 40 Meter bands, 4-5 watt output, CW, RIT, and sidetone through headphones or external speaker. Also included are push button choices of 3 bandwidth filters and three tuning rate adjustments from the provided firmware program.
Shown here is the stock, front and rear panels. The Select and Function buttons work in tandem. Each of the three functions allows three choices via the Select button. The BW (bandwidth) function allows choice of Wide, Medium or Narrow. The Step function provides tuning rates of 100 Hz, 1Khz or 10Khz. The User function is left undefined for the user to modify for his/her needs. Note there is a LED set between T’s of the Ten-Tec logo. That LED is pre-programmed to flash once at each step- change of frequency providing you feedback to where you are on the dial.
Plug in 10-15 VDC power, headphones or speaker, antenna and key and you’re ready to go.
Although its ready to use out of the box, the really fun part starts when you decide you want to modify the Rebel. Programming is done through a mini USB connector attached to the Arduino compatible ChipKit board inside the Rebel. Its accessible behind a removable plate as shown above.
Both Windows and Macintosh can be used to program the Chipkit. It’s understandable that many Hams don’t have the time, skill or interest in learning to “write code” for the Rebel. However, that needn’t stop you from upgrading its software. There are many talented Hams who do program and many support the Open Source spirit and share their code on Yahoo. This has led to some very nice features being added to the Rebel. If you can type on a computer it’s not hard to enjoy these program upgrades without ever writing a line code.
I took a middle path here and started teaching myself the variant of “C” programming used by Arduino and similar micros. There are a number of books and course available for the beginner.3 With a rudimentary grasp of C, I’ve been able to “mix and match” bits of code from various versions of the Rebel’s code and occasionally added some of my own invention. The most popular code version in use is labeled Rebel Alliance written by a group or early users who collaborated via a Yahoo group. It can found on the Ten-Tec Rebel Model 506 Yahoo Group.
My first mod was to incorporate a small band change relay board designed by Jeff Fletcher AF5PI to eliminate the need to open the case and move jumpers to change bands. The Rebel Alliance software had already incorporated a choice to use the board. The code watches for a button push then powers the relays.
3 Beginning C for Arduino by Ph.D. Jack Purdum, Programming Arduino by Simon Monk, Arduino Course for Absolute Beginners by Michael James of the Open Hardware Design Group
Next I added a zero beat indicator found in my junk box from a pervious project. I used the Ten Tec Logo LED, repurposing it to indicate when a station was at zero beat of around 700Hz.
Then my goal was to add a display. Ten-Tec did not make this easy leaving no space in their case design. One Ham tried an OLED display because it was tiny enough to squeeze onto the front panel and bright enough and easy to read. I really liked this idea.
However, as promising as this display seemed, it was difficult to
program and caused problems with the existing code. After months of research and testing I was successful in adding an OLED display.
Adding the display, however, seemed to introduce a problem with cw keying. After much head scratching I determined the existing software keyer was really the culprit due to execution timing issues it’s coding created. My solution was to remove that segment of code and incorporate an internal hardware keyer to replace it’s function. It took a little searching to find one small enough for this situation. I chose a SMT version of the PK4 keyer. Literally the size of a postage stamp, it easily fit inside the Rebel and added a number of nice keying functions too.
These modifications make the Rebel much easier to use but my particular installation required another mod, a PTT line out. I use the Elecraft KPA100 to match my antennas. To efficiently use it’s tuner, with or without the amplifier, requires a PTT signal to ground. This is an easy mod which I’ve added to other radios. It uses a 2N7000 FET as a switch to provide a low-going signal on transmit.
To add this to the Rebel I programmed one of the available microprocessor input/output lines to go logically HIGH on transmit which then provides 5 Volts to the 2N7000 Gate pin causing the FET’s Drain to go low effectively bringing the PTT line to ground.
Next, just for the fun factor of it, I replaced the Ten Tec Logo LED with a Red/Green Bi-Color LED (two LEDs in one). This allowed me to restore the frequency-step flash using the red element. The green portion of the LED illuminates when I achieve zero beat.
To facilitate connecting all these mods I installed a prototyping shield which is a PCB made to plug into an Arduino’s connectors.
The result of all this fun is a small 5 watt cw transceiver that now boasts a built-in memory keyer, zero beat indicator, PTT line out and an attractive display that I’ve programmed to not only show TX/RX frequency, RIT indicator, Power Input, Graphic S-Meter but also proudly displays my callsign.
During all this fun “hacking” of hardware and software, I’ve enjoyed actually making lots of QRP QSOs. The receiver is sensitive and the filtering is adequate under most conditions and my signal reports are excellent. Considering the low cost (around $200), this radio is a lot of fun and one that continues to evolve.
Thanks to Ten-Tec’s choice of an open source, Arduino-based micro controller I can continue to change, improve and truly make this my personal radio.