My experience with the construction of the OK2XDX weather receiver

One of my friends asked me to write my experience with the receiver kit for meteorological satellites from OK2XDX. Surely you all already know her from the magazine Amatérske Rádio, because it has already been published twice. So I won't tell you about it from the functional side.
The whole receiver is:

• double mixing superheterodyne and pll

 

• frequency range 137 -141 MHz

 

• the debugging step is 10 kHz

 

• sensitivity 0,6 uV

 

• powered 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 that way, that I ordered it for my friend in the Czech Republic, to whom I sent money. And he sent us the kit. Although the manufacturer offered me the option, to send him the money in an envelope and he will send us the kit, but I did not trust this method.

The kit had painted and tinned circuit boards, so the PCB work itself was very clean and good.

I proceeded in the usual way when installing the DPS, from the lowest part to the highest. You had to be careful here, because some parts were not installed due to later tuning. I threw everything there! The metal cases of coils and crystals must not lie on the board, so that there are no unwanted connections with a double-sided PCB.

The revival began by connecting the establishment to the source, in my case I shorted the source. It also had a current fuse 🙂 I found the error immediately, it was a protective diode, which I connected in reverse. I already had my suspicions during installation, that, on the contrary, it will be installed. Next, with the help of a friend and his wobbler, I tuned the input filters, that 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 exam 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 was therefore clear, that the PLL synthesis has gone, specifically the SAA circuit 1057. I could not find this circuit in Bratislava, and so I finally bought it during a temporary job 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 after 145,0 MHz. But at a frequency of approx 141,0 MHz behind the PLL hinge. This state can only be reached by manual tuning. Through the scan function, the receiver is tuned only from 137,0 – 141,0 MHz. The author was probably counting on the use of the device either for weather satellites or 2 meter.

It is interesting, that the frequency can be easily controlled from the computer, which makes it possible to create a separate device for receiving images, which does not require maintenance. 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 distributor Miroslav Gola OK2UGS www.emgola.cz.

Martin (dolphin)