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I just returned from this years International Packet Radio Conference (IPRT) which was held at Darmstadt University of Technology. The scope of the conference is digital data transmission in amateur radio in general and is not limited to packet radio using the AX.25 protocol as the name might suggest. Their were ten talks in two tracks, a bit less than last year.
In the first talk, Michael Zähringer, DB3MZ, spoke about Galileo, the global satellite navigation system build by the European Union. As amateur radio operators are operating as secondary users on a frequency range (23 cm) also used by Galileo, some interferences are expected. For transmitting the time signal to the receivers used for computing the position their position on the sphere, Galileo is using a 50 MHz wide pseudo noise carrier which is close to the noise limit and will thus not interfere narrow band amateur radio transmissions. However, amateur radio transmissions are likely to interfere Galileo navigation receivers as their Automatic Gain Control (AGC) will react to the strong amateur radio signal and makes Galileo signals undecodeable. This effect was demonstrated in a test area in Berchtesgaden where six Galileo transmitters are installed at the surrounding mountains. During experiments with prototypic Galileo receivers, their AGC reacted to the narrow band packet radio data transmissions of nearby packet radio digipeaters operating on the 23cm band. As the speaker mentioned, Infineon reacted to this problem by limiting the AGC to broadband signals only.
As this part of DB3MZ’s talk highlighted operational problems, the last part focused on applications of the Galileo time signal. As Galileo has a more accurate phase noise than GPS, it can be used for low power, low bandwidth transmissions. The amateur radio operator W6NEY, professor at Stanford University, with Coherent CW (CCW) using GPS which only requires 5 to 10 Hz bandwidth and thus enables efficient low power transmissions. These experiments can be continued using the Galileo signal.
A nice story in his talk was about the decryption of the code used by Galileo for encrypted signals. This code was decrypted by hackers of the German Chaos Computer Club (CCC) and was changed by Galileo. This reminds be a bit to the cat-and-mouse game played by a German pay TV provider, who frequently change his encrypted code whenever someone cracked it. As the latter told us, people are always able to crack the encryption. Thus the question rises up, how often they are going to change it …
Thomas Kleffel, DG5NGI, presented three boards used for transmitting DVB-T/S, gPSK, ATSC, gMSK, … signals in the scope of digital TV and broadband data communication. The MiniMod board he constructed and presented can be used for narrow band DVB-S (> 1.8 Mhz bandwidth) TV signals, as currently used in northern Germany, narrow band DVB-T (> 2 Mhz bandwidth) and gMSK. The latter is a interesting mode for amateur radio operators as the requirements of the power amplifier (PA) in terms of linearity are relaxed and a normal class C PA used for analog FM signals is enough. The second board presented in his talk can be used as an Ethernet over DVB bridge for broadband data communiction (e.g. for D-Start or Echolink access). It is more expensive than using cheap WLAN hardware, but more flexible, as arbitrary frequency ranges can be used as well as linear amplifiers.
Rein Couperus, PA0R, introduced PSKmail which he has developed in the past three years. This mode is used for accessing mail and the Web (”the slowest interface to Google”) via HF on long distance. PSKmail is using PSK for modulation and data transmission along with a ARQ for re-transmission of lost frames. Unlike PSK63 which reduces its bandwidth from 2,4 kHz to 500 Hz when the signal reception decreases, PSKmail reduces its frame size by using a constant bandwidth. PA0R demonstrated how electronic mail can be downloaded from servers and accessed locally by the mail user agent (MUA) Evolution in Linux, or to access the Web (including carrying out Google queries) by wget.
Jochen Berns, DL1YBL, discussed Icom’s Digital Voice system D-Start and the experiences obtained by operating D-Star repeaters in Germany. The subsequent discussion was controversial as the vocoder used by D-Star is closed source and needs to be licensed. This limits the experimentation with a new technology and may contradict the experimental nature of amateur radio.
All in all, it was a nice event and I’m looking forward for next years IPRT, where an anniversary can be celebrated–the 25th IPRT. See you next year!
