First time in Japan

This morning on 12 m I got my first reply from JA. OM JF2IWW was 539 with deep QSB, but he copied my 5 W and gave me a 439. Then fading took him away and I missed most of his message, but I heard his final greetings.

I would like to know more about his power and antenna, but there is nothing online.

How cellphones vibrates

Vibration alert in mobile phones is accomplished with a small but powerful electric motor that spins a small asymmetrical weight. In the picture below the motor is the "horizontal cylinder", while a 50 €cent coin gives an idea of actual size. The third object is a 1F 5V supercapacitor.

Small motor, 1F 5V supercap and a 50 €cent coin.

What do these have to do in my blog? Well, I bought two rubber band powered airplanes as a gift, and as soon as I saw them flying I immediately wanted to "improve" them with a longer flight time. How? My idea is to use the small motor and the supercap. The total weight is about 5 grams and the motor runs longer than 10 seconds off the supercapacitor. I need to figure out a way to easily power the motor after launch: a normally closed tactile switch could be handy.

Nevertheless, a bigger challenge is how to connect the motor to the propeller...

Not much gong on (on 10 metres)

As usual, Spring decreases my will to build circuits (that's why there were no updates for a while). But I feel the urge to radiate some RF too. So I threw out of the balcony a 1/4 wave radiator for 24/28 MHz and last Monday I could work W1AW/1 in PA with 5 W SSB. After that ... just two continental QSOs in PSK31 throughout the week. A WSPR session brought in some North America reports, one night.

Sadly, the culprit is not a deaf or noisy antenna, but closed (and empty) bands. Will keep monitoring 10/12 m, then maybe I will lengthen the radiator wire to 15 m.

AD9850 board and temperature

My AD9850 DDS chip and the 125 MHz canned oscillator run pretty warm to the touch. No info were found online, so here you are my values in room temperature (23°C): both stabilise between 45 and 48 °C.

I let it run for few hours and it didn't break nor catch fire.

Chip temperature is not output-frequency dependant, but output-frequency depends on the oscillator temperature. Touch the canned oscillator and it will change of few Hz. I am wondering if I should add a small heatsink to the oscillator. Is it worth?!

Arduino controlled AD9850 DDS signal generator

Been blog-silent for a while, but my AD9850 DDS is now complete. The Arduino (Nano) code evolved day-by-day while assembling the circuit. I re-assigned some pins to simplify wire routing and implemented an easily extensible menu. My code is based on AD7C work and it is available on request.

I have added a scan function with user settable lower/upper frequency limits.

I have added a menu driven with a resistive potentiometer, which requires only one button for confirming the action and theoretically can host dozens of functions. While it is not an innovative idea, it is very comfortable to use as long as there are 5-to-10 total choices.

I am now using a TWI/I2C interface to the display, which uses 4 instead of 8 total wires.

DC is provided with a step-down regulator. I will add DC filtering capacitors near the Arduino and DDS boards.


That's two knobs and one display that now require a suitable housing.

Playing with AD9850 board

While trying to understand all the pins of the AD9850 board (marked "SR-HC08"), I could not find the square wave output. A good sign was that QOUT2 was at +5 V and QOUT1 at 0 V. A simple adjustment of the onboard trimmer (duty-cycle control) activated the AD9850 internal comparator and there appeared the square wave.

Therefore output pins in my board are:

• ZOUT2: sine wave through an LPF
• ZOUT1: direct sine wave
• QOUT2: square wave
• QOUT1: square wave (180° shifted)

 If you don't need the square wave output disable it with a fully (C)CW rotation of the trimmer.

Musings about going Bluetooth

I occasionally receive a question about transporting bidirectional audio over Bluetooth and not only CAT controls. The answer is "technically possible", but there are two possible scenarios.

Voice

This is the case for handsfree operation, be it in on the move or just around the house. Using the VOX this is possible, but on the RTX side we need a Bluetooth "master" device. In order to establish a Bluetooth link there must be a master initiating the connection towards a slave. Since all in-ear handsfree earphones are "slaves", there is need for a master device connected to the transceiver: I have not found yet a master bidirectional audio Bluetooth module (maybe the one mentioned in an earlier post?!).
The discontinued Jabra A210 seems to be the only device with such characteristics, and it must be modified in order to work with a transceiver.

Digimodes

Since digimodes are generated in the computer/tablet/smartphone, we already have a master Bluetooth device. So theoretically any handsfree BT earphone would work. Besides difficulties in modifying such tiny electronics, I have been told that the audio encoding and compression operated by BT audio devices introduces unacceptable noise and phase distortion. The former affects the ability to copy weak signals at our antenna, the latter makes it impossible to work phase-based digital modes (PSK31, for example, while RTTY would probably work).

So DDS I

The discussion and web-xcitement around the MINIMA transceiver designed by the BITX author added yet another project to my to-do list. Before buying an Si570 for MINIMA, I still had to play with an AD9850 DDS board I recently bought.

Wiring it up to an Arduino Nano clone was a matter of half-an-hour. A working Arduino sketch was easy to find thanks to the work done by AD7C: in an hour my DDS signal generator was up and running.

The code is simple and gets the job done. I did a few easy changes:

• corrected the "MHz" label (was "Mhz")
• delayed the store timing of the latest tuned frequency (2s, now 20s, not to stress the uC EEPROM)
• added a visual feedback whether the latest frequency has been stored or not

Even to my non-calibrated frequency counter, the DDS frequency was off by ~ +50 Hz. This was corrected with a simple math that I will describe in the future.

To my surprise the whole circuit draws about 165 mA: that's a lot of current! That's 0.8 W or power consumption. Even if the AD9850 DDS offers a huge frequency agility in an HF RX/TX, that's at the expense of current consumption. I will not give away my QRP frequency XTALs just yet!