Jeden môj kamarát ma poprosil aby som napísal moje skúsenosti so stavebnicou prijímača na meteorologické satelity From OK2XDX. Iste ju už všetci poznáte z časopisu Amatérske Rádio, lebo bola už dvakrát publikovaná. Tak po funkčnej stránke Vám ju približovať nebudem.
The entire receiver is:
- double mixing superheterodyne and pll
- frequency range 137-141 MHz
- the tuning step is 10 kHz
- sensitivity 0.6 uV
- powered by 9-12V, 90mA
The problem was how to import the kit at all, because Czech products cannot be delivered to Slovakia by cash on delivery. I solved it by ordering it for my friend in the Czech Republic, to whom I sent the money. And he sent us the kit. The manufacturer offered me the option to send him money in an envelope and he would send us the kit, but I did not trust this method.
The kit had printed circuit boards painted and tinned, so the PCB work itself was very clean and good.
When installing the PCB, I proceeded in the usual way, from the lowest component to the highest. Care had to be taken here, because some parts were not installed due to later tuning. I threw everything in there! The metal housings of the coils and crystals must not lie on the board to avoid unwanted connections with the double-sided PCB.
The revival started by connecting the device to the source, in my case I shorted the source. It also had a current fuse 🙂 I found the error right away, it was a protective diode, which I connected the other way around. I already had a suspicion during installation that it would be installed on the contrary. Next, with the help of a friend and his wobbler, I tuned the input filters, it was quite interesting work with coils.
The penultimate thing was to set the tuning voltage on the PLL synthesis, this task was followed by the test itself, but nothing could be tuned on the receiver.
Therefore, my first suspicion fell on the receiver circuit itself, but considering that the sound went, I checked the tuning voltage, which did not change with the change in frequency, and therefore it was clear that the PLL synthesis had gone, specifically the SAA 1057 circuit. I could not find this circuit in Bratislava, so I ended up buying it during my internship in Austria. I replaced the circuit and the receiver works perfectly and I am happy with it.
It is worth noting that a program for tuning from 137.0 MHz to 145.0 MHz is burned into the microprocessor. But at a frequency of about 141.0 MHz, the PLL hangs behind. This state can only be reached by manual tuning. Through the scan function, the receiver is only tuned from 137.0-141.0 MHz. The author probably calculated using the device either for weather satellites or 2 meters.
The interesting thing is that the frequency can be easily controlled from a computer, which makes it possible to create a separate device for receiving images, which does not require an operator. I haven't tested this option yet, but I will definitely try it.
If you are interested in a kit or information about weather satellites, you can find them on the website of author Radek Václavík OK2XDX www.QSL.net/ok2dx , or at the distributor Miroslav Gola OK2UGS www.emgola.cz.
Martin (dolphin)