Four on longwave

Most weekends, except in summer, I am transmitting my radio signal on longwave, ( 2190m / 137.7KHz ), and hoping someone will reply. Usually my signal goes unanswered as no one else is about; but last night Marek, a Polish radio amateur, callsign SP2OVY, from near Gdansk, called me. I had never received his signal before. So I assume that he has only recently begun to transmit on longwave. To my knowledge there are now 4 Polish stations, including myself, who have transmitters for the 2190m band; though I am aware of a few others who monitor on receive only. Two years ago I was the only one active on longwave in Poland. So the numbers are gradually increasing.
The distance between Marek and me is only 277kms; but I was happy my signal made it that far as snow on my antenna had significantly detuned it. We had a successful 2-way contact, ( report "O" bothways ), ending in the early hours of this morning.
The screen capture shows his slow morse ( QRSS ) signal to which I have added the letters; of course 'E' and 'N' were the following two letters on the next screen capture, ( not shown ).
I am still using the same home-made transmitter and antenna which I featured on the blog on 25th January and 19th February.

Adjustable voltage for the ex-PC PSU

The discarded computer power supplies which I modified, ( see January 26th and March 7th ), are very useful items of equiment to have on the bench in the workshop; 12V for my frequency synthesiser project and 5V for microcontrollers. They are, of course, fixed voltage supplies. There will be times when other voltages will be needed. I am thinking in particular about 9V and 3V. So I made an adjustable series voltage regulator to connect externally to the 12V power supply. The regulator uses a linear voltage regulator IC, RCA type CA723CE, or National Semiconductor type uA723CN; both have identical pin assignments, and are directly interchangeable, ( same package outline 14pin DIP ). Unfortunately two different, separate circuits are needed to provide 3V and 9V; the difference being the connections between the resistive potential divider and the error, ( "long-tailed pair" differential ), amplifier. For the time being at least, I decided to make just a 9V version for permanent use, ( the output voltage is adjustable between 8.43 - 9.81V ); but I also built a 3V version on experimenting board to check it, ( the output voltage range was 2.8 - 3.6V ).
The xA723Cx IC on its own can provide a maximum of 150mA output load current. This is insufficient for general purpose use on the work-bench; more current should be available. So the IC drives a 'pass' transistor rather than the load directly; but the output will be 0.6V less. Just about any power switching transistor capable of passing a few amps is suitable. From my stock I pressed into service an ancient and hitherto unused Motorola type BU326A, rated at maximum 8A, and fitted it to a small 2.9degC/W heatsink.

AF Marker Generator

I have four 2048KHz quartz crystals, probably originally in some old 32 channel PCM telecomms equipment, and was thinking how I might use them, or at least one of them. I also have the same number of CMOS logic binary divider ICs, types HCF4060BEY and CD4060BE. 2048 = 2e11; dividing it by 2e12 ( 4096 ) will produce a 0.5KHz square-wave from the divider chip.
In my circuit, the crystal is used in a 2048KHz oscillator to clock the divider chip and the 0.5KHz square-wave is taken from the /4096 output on pin 1. A resistive potential divider reduces the level of the square-wave to 1.05V on the output phono socket.
As a square-wave is the sum of harmonically related sine waves, in the frequency domain there will the fundamental 0.5KHz signal and its odd numbered harmonics; 3rd, 5th, 7th, 9th etc. For my purposes the most useful signals are the fundamental, 3rd and 5th harmonics; 0.5KHz, 1.5KHz and 2.5KHz respectively, as these lie within the AF band 300Hz-2.7KHz typically used in radio communication, and can be used as accurate frequency calibration markers.
I have connected the marker generator to the sound card in one of my PCs in order to display the audio spectrum. With the cursor arrow placed as accurately as I can manage on any one of the signals, e.g. the 3rd harmonic near the band centre, and reading off the frequency there is a frequency error of +7Hz due to the inaccuracy, compared with the nominal, of the sampling rate of the sound card input.
After that slight digression I had better get back to PIC programming, or maybe I'll make a start on putting together the pre-amplifier, ( see June 16th ).

On display

Seeing is believing ! I programmed the frequency synthesiser, which I am in the process of building, for an output signal on 137.700KHz. Both the display on the Thandar PFM200A frequency counter, ( connected to the output ), and the display on the synthesiser, ( connected to the microprocessor ), agree. What a relief.
The next task is to make it tuneable up and down, ( probably in 1 and 10Hz steps ), implement band changing and at the same time make sure the display updates correctly.

MyDev2 replaces MyDev1

PIC18F4550 version

PIC18F4685 version

Schematic - note Vcc connection depends on usb-powered or self-powered application

Development boards for microcontrollers are essential for debugging code and checking hardware peripherals before committing to the final build-configuration.My first microcontroller development board, which I called "MyDev1", has served me quite well; see 25th January. It is a typical, solderless, experimenting board; component leads are a push-fit into the holes. Its limitations, however, began to become apparent; noisy, intermittent connections, lack of flexibility and a real nightmare if I had ever attempted to use it with 40 or even 28 pin microcontrollers and interfacing with several hardware peripherals at once. Having unreliable connections is a really bad situation when the microcontroller is waiting, or looking, for changes.It was therefore time to upgrade to a better system; so I have produced "MyDev2". Now it is much easier to reconfigure for different peripherals, e.g. display, keypad, rotary encoder, comms ports, and to check their operation. Of course, I haven't omitted the LEDs, and "MyDev2" has many, ( different colours for different ports ), as it is always nice to see pretty lights as a visual indication of I/O port output state ! I could not avoid solderless connections entirely; but those are of a high reliability using good quality pin-headers.
"MyDev2" connects to the Microchip ICD2, ( In-Circuit Debugger No.2 ), for programming and debugging operations, thereby replacing my original home-made programmer, ( see 25th Jan, 8:06PM, purple box ).
Using a development board I was easily able to change between two mechanical rotary shaft encoders, ( control with knob ), from different manufacturers, choose the more appropriate one for my final application, and 'fine-tune' the PIC code to suit.
Incidentally, the microcontrollers featured in the pictures above are 40 pin Microchip parts, ( lower ) type PIC18F4685-E/P, and ( upper ) type PIC18F4550-I/P which incorporates a USB interface.