10 MILLIWATT QRSS BEACON TRANSMITTER FOR
30 METER KEYED BY A WEBBROWSER
(2010)

KLIK HIER VOOR DE NEDERLANDSE VERSIE


The beacon transmitter of 10 milliwatt with Light Dependend Resistor (LDR).
The beacon transmitter is keyed by the LDR.

Experiments with very low power QRSS beacon transmitters
There is a group enthusiastic radio amateurs that is doing experiments with very low powers. That is possible by using a low CW speed (QRSS speed). Most of the activities can be found in a band of only 100 Hz, namely 10140.0 to 10140.1 kHz in the 30 meters amateur band. Signals are decoded with a special software program. My beacon transmitter could only be frequency modulated with a square wave with a frequency shift of 4 to 5 Hz. But for the serious work, in morsecode the call, QTH locator or transmit power had to be transmitted. But how can that keying with morsecode be realized?


The LDR is placed in front of the monitor screen. The white square
on the screen blinks on/off in the rhythm of the morsecode.
This is done by a HTML program running in a webbrowser.

Keying with a webbrowser
It was not easy to find a simple solution for keying the beacon transmitter with morsecode. Mostly, a micro controller circuit is used. But how can you key the transmitter with a PC? A printerport and RS232 port are history. It can be done with a special interface for the USB port. But which software do you have to use for that? And that works of course only with Windows-XP, but not with Vista...
Then I had the idea to use software that you can find on every PC, namely a webbrowser! We make a simple HTML program that does blink a square on the monitor screen white/black in the rhythm of the morsecode. In front of that square, we place a light dependent resistor that keys the beacon transmitter. That works for all operating systems, Windows 95 to Windows 7 and newer, Linux, MAC-OS, the webbrowser controls everything! And we do not have to buy or hack and install software. And everyone can modify the program with a simple ASCII text editor (Notepad) to his own demands. It does not have to be a fast program and the timing is not critical. A dot lasts 3 second and a dash 9 seconds. Is that dot or dash a little longer or shorter, nobody will notice that.


The HTML program running in a webbrowser, here Google Chrome.
The white square blinks on/off in the rhythm of the morsecode.

The program
The program is using Javascript, that has to be enabled in the webbrowser. But normally that is already the case, most HTML applications on internet do use Javascript.

Click here to see the HTML program running, that will make clear to you how it works.

Click here to download the zipped version of the HTML program.

Click here to download a zipped version that transmits in time synchronized 10 minute intervals.

You can modify the program by means of an ASCII text editor like Notepad. In one of the first lines after "Data", you have to fill in the desired morsecode. And after dottime the keying speed in milliseconds (normally 3000 ms for a dot). By means of style sheets, two squares are defined, a white square and a black square. And by means of a timer interrupt routine named "function NewTime()" and the function "innerHTML" for modification of a part of the screen, everything is controlled. After that the morsecode is transmitted, the HTML program is loaded again and run by the webbrowser. During a transmission, it is possible to modify the HTML program. I can do that from any location, as together with the webbrowser, a FTP program is also running on the PC. But there are other possibilities for that. And on the PC, also the program ARGO with simple receiver is running, so that I can see from a remote location if everything is going well.


Circuit diagram
big diagram

Description of the circuit diagram of the transmitter
A crystal oscillator with a BC547 transistor is buffered by NAND1 and NAND2 and amplified by NAND5 to 8. The circuit with NAND3 and NAND4 is a square wave oscillator. When the switch is opened, the transmitter is frequency modulated by this square wave. But also in amplitude. During the positive half of the square wave, NAND5 to 8 are all switched on and the transmit power is 10 mW. During the negative half of the square wave, only NAND8 is active and the transmit power is only 1 mW (or 0.1 mW, depending on the used resistor values). When the switch is closed the transmitter is keyed by the LDR. The capacitors of 1 uF and 10 uF do suppress the flickering of the screen and other interferences.
During the transmission of a dot or dash, the transmit power is 10 milliwatt. During spaces, the transmit power is 1 milliwatt (or 0.1 mW, depending on the used resistor values) and the transmit frequency is lowered with 4 to 5 Hz.

Temperature stabilization
The frequency has to be very stable. It is quite difficult to adjust the beacon transmitter on a frequency of 10140.0 tot 10140.1 kHz and to avoid drift due to temperature changes. A temperature correction circuit was made with a NTC resistor and a varicap. The drift could be reduced considerably. For a positive frequency drift correction, you have to connect the NTC in accordance with the diagram. For a negative correction, the NTC resistor and 68k resistor have to be exchanged. Of course you can also take a NTC resistor with a different value. Exchange the 68k resistor then for one with the same value as the NTC. Increasing of Cs and reducing Cp increases the correction, reduction of Cs and and increasing of Cp does reduce the correction. Finding the correct value is done by of trying out various values of Cs and Cp while cooling down and warming up the transmitter.

The Light Dependent Resistor (LDR)
It is important to keep a distance of at least 0.5 cm between the screen and the LDR. Otherwise, the high voltage of the screen can disturb the LDR. The flickering of the screen has also to be filtered out. And you have to avoid interference from daylight by screening the LDR and screen with a piece of cardboard or so. By using a LDR we have a full galvanic isolation between the PC and the 10 milliwatt beacon transmitter! Of course you can modify the program so that you have a second square with second LDR to switch other things like power or switching between transmission and reception.


The circuit mounted in a plastic housing on an unetched piece of PCB.
An extra coil in series with the crystal was necessary to tune to the correct frequency.

Construction
The circuit is mounted in a plastic housing on an unetched piece of PCB. That is simple, quick and it is easy to change the circuit. That last advantage is very important, the final design was modified considerably. The transmitter is supplied by an AC/DC adapter.

Results
It is a strange experiment. The 10 milliwatt transmitter is switched on and... The needle of the power meter does not move! And it is even a QRP power meter! But how do you get reception reports? Quite soon I received an e-mail with screenshot from Dusan, YT1DL. Dusan many thanks, with this report the experiment was already 100% successfull! Not only the high shift with dots and dashes with 10 milliwatt was visible, also the lower shift with pauses between the dots and dashes of 1 milliwatt was visible! Dusan does not use the program ARGO but Spectran.


Reception report from Dusan YT1DL, received by e-mail.
Not only the 10 mW, but also the 1 mW shift (pauses, 4-5 Hz lower) is visible.

But there are other possibilities to collect reception reports. There are amateurs who have their receivers coupled to internet. The reception results are continuously refreshed. You can see these results on internet (Search via Google for "QRSS grabbers"). The results here below are obtained via these QRSS grabbers. Totally, the beacon transmitter has transmitted during 3 days.


Reception report of the QRSS grabber of G4CWX in Bristol.
Also here the 1 mW shift (pauses, 4-5 Hz lower) is visible.


Reception report of the QRSS grabber of I2NDT in Bergamo.
Also here the 1 mW shift (pauses, 4-5 Hz lower) is visible.

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