The operation of automated Amateur Radio stations at the current location has long heritage, dating back to the first installation of a Packet Radio digipeater using the callsign DB0HDF in the 1990s.
Initial tests of Packet Radio digipeater hardware using the callsign DB0HDF were conducted from the home of Wolfgang, DG0OBR in Hermsdorf starting in 1994. A first viewing of a dedicated site for permanent installation of a digipeater was arranged in March of 1994. An agreement for use of the site was established with the local housing association and signed in April that year. Following a lengthy process involving changes to the official coordination documents with both the regulatory body (Federal Post and Telecommunications Agency) and the amateur radio club (Deutscher Amateur-Radio-Club e.V.), electrical connections as well as the first antennas were installed on the current site of DB0HDF in November 1995. Since then, a number of different technical experiments and modes of operation have been supported from the site over the years.
Commercial interest in the site’s rooftop sprung up around 1997, when Vodafone (formerly Mannesmann) started establishing cellular network coverage in the area. Since then, both cellular (2G/3G/4G) services and the amateur radio services continue to co-exist at this location. The following sections summarize the history of the individual developments on the amateur radio side.
A key upgrade made to the site was the installation of a WiFi link to Torsten, DL4APJ in March 2011. Using this link, installations on the site could be connected to the Internet, which was a major consideration for applications such as APRS I-Gates, D-Star and Echlink operations, as well as remote monitoring and control.
A Packet Radio digipeater was the first installation put in place at DB0HDF. After initial testing off-site, an RMNC-based system including an attached mailbox (based on DieBox 1.9) went into operation in May 1996. A user baud rate of 1200 Baud in simplex operation on 438.175 MHz was used. In addition, two digipeater links had been coordinated: DB0GER in Gera as well as DB0APO in Apolda were the first link partners. Plans for a third link, towards DB0HOT (Hohenstein-Ernsttal), were underway already before the digipeater became operational. In July 1996, an upgrade of the user data rate to 2400 Baud was implemented, which could be used in parallel to the existing 1200 baud simplex link. Very soon after, dedicated antennas for additional 9600 Baud connections were installed. Connectivity using 9k6 baud were first possible starting in October 1996. Already in 1997, a new permanent link towards DB0HOT was commissioned, and additional equipment for another link towards DB0INS (Inselsberg) installed.
Early in 1998, the 2k4 user link fell out of use and was disabled. Soon after, during summer, the 1k2 user access was disabled and its hardware modified to support a link towards DB0APD. To optimize throughput for 9k6 operations, a 70cm duplex frequency pair was requested to replace the existing simplex user link. The simplex link was finally disabled in 2000 and another link towards DB0HOF (Hof) established. A final link to DB0SLF (Saalfeld) was set up and became operational in May 2000. From June 2000, a second 70cm duplex link was etablished: An omnidirectional antenna continued to serve 9k6 users, a directional antenna on a different pair could be used for higher baud rates up to 153k6 baud.
With good connectivity established following a few years of intense development and experimentation, the packet radio digipeater remained in operation under the supervision of Wolfgang, DG0OBR in the early 2000s. With as many as five directional RF links (DB0INS/DB0APO, DB0SLF, DB0HOF, DB0GER, DB0HOT) and two user entry points being operational during the peak of the German packet radio network developments.
At first, the quickly increasing availability of domestic internet connectivity in the 2000s further complemented the packet radio network through TCP/IP-based links and user connections. However, in the second half of the decade, the internet slowly obseleted and outpaced the developments in the packet radio space. The digipeater remained on air until around 2008, but was at some point decommissioned before activities surrounding new digital voice communication modes took over their established frequencies.
The first APRS digipeater in Hersmdorf went into operation in September 2005, under maintainership of Rolf, DL2ARH. This digipeater was assigned DB0SHK (for Saale-Holzland-Kreis, indicating the coverage area). Initially, a TNC2 and Windows-based digipeater software were used. This mode of operation was continued until about 2010, when modernization of the equipment used on site began. As a first upgrade, DB0SHK was re-built based on the APRS4R router distribution. This significantly shrunk the power consumption of the installation. The new digi became operational in July 2010. Shortly after, a Netgear WGT634U router was acquired. Due to persistent memory issues with the APRS4R distribution, a more lightweight APRS digipeater software alternative (aprx) was adopted.
After an initial testing phase of this new configuration at the QTH of Rolf, DL2ARH, its 19" unit was integrated into the D-Star equipment rack and both transferred to the site of DB0HDF in March 2011. This configuration has been in use without notable amounts of maintenance for many years. The aging router hardware was finally replaced by a Raspberry-Pi-based SBC in 2021, however the same software configuration continues to be used and remains very reliable. A TNC2S is still employed for modulation and demodulation.
The second mode of operation established at the site of DB0HDF was analog amateur television (ATV). A first set of frequencies were coordinated by Rolf, DL2ARH and an initial repeater setup went ’live’ in 1998. The ATV repeater strictly used yet another callsign, DB0HL. Initially, only a 13 cm uplink (2380 MHz) and 3 cm downlink (10194 MHz) were used. After initial testing off-site, antennas and the repeater hardware were installed on the roof of DB0HDF in September 1999. The FM ATV repeater supported color TV and stereo audio using a 5.5 MHz audio subcarrier.
A bidirectional link towards DB0THA (Schneekopf) on 3cm (10160 / 10380 MHz) was etablished, connecting the repeater to the emerging ATVlink system in November 2003. A number of interesting technical options were added to the ATV repeater over time: A local 2m RX feeding into the audio channel of video transmissions could be used for talk-back purposes. Additonally, an early EchoLink gateway was added in early 2003, operating at the QTH of Rolf, DL2ARH. This circuit was later also used to provide access to Shortwave bands, via the same 2m QRG. Additionally, a second audio subcarrier on the directional link towards DB0THA was used to test operation of a fast packet radio link.
In 2005, a decision was made to rebuild the ATV repeater, housing all components in a new equipment rack, to provide more flexibility, more complex linking options, etc. This development at the height of the ATVlink project came to a halt in around 2007, when many ATV repeaters nationwide were forced to scale down operations significantly due to restrictions put in place in former Bundespost/Telekom sites. A few key inter-repeater links were lost to these restrictions, severely limiting the usefulness of ATV for communications beyond the local radio horizon.
As a potential remedy to this situation, solutions involving an internet-connected repeater were devised. As part of weekly project gatherings involving Rolf DL2ARH, Stefan DK3SB and DL3YC, initial plans for a third iteration of the ATV repeater were drafted in 2015. Some developments on a custom video matrix, a digital/analog conversion module and control software was started, but the project finally did not gain traction. As such, the repeater continued to operate only in the form of a transmit-only beacon into the 2010s, before being dismantled. Operation on 10 GHz was superseded by the installation of a new 10 GHz beacon in 2022.
Voice Repeaters (FM/D-Star)
Following the decline of user counts accessing the packet radio digipeater at DB0HDF around 2008, first discussions surrounding a modernization of the repeater site surfaced. Up to this, no voice communication repeater was installed at the site. The recent emergence of D-Star as a digital mode was attractice not only as an opportunity for voice communications, but also its data transfer promises. These initially suggested that some packet radio functionality (local bulletins, APRS) could be at least partially covered by D-Star as well. Ideas continued to evolve during 2009, while Torsten, DL4APJ and Rolf, DL2ARH initiated discussions with SysOps of other D-Star repeaters, which were beginning to spring up around Germany. The key system components for building a D-Star repeater (proprietary ICOM hardware) were acquired in November 2009 and permission was saught from the regulator bodies to re-use one of the available packet radio frequencies for this purpose. Late 2009 further saw the acquisition of many other hardware components (a PC, duplex filters, monitoring electronics, power supplies, …). The mechanical and electrical construction of the new repeater 19" rack by Rolf, DL2ARH, was completed the same month.
An initial installation of the ICOM Gateway Software and bring-up of the system was completed in early December 2009. Before the end of the year, the new repeater was registered with the ICOM trust server, which made features such as callsign routing available. The German national reflector (initially DPlus REF006 C) quickly became an established part of the repeater operation, filling the local frequency with life and encouraging QSOs in this new mode. A number of further RF performance improvements for the repeater were implemented (a pre-amplifier, an improved duplex filter, a transmit frequency notch for the receiver path, …) during early 2010. Continued issues with synchronization to the US trust servers plagued operation well into fall of the same year. These issues were finally resolved out in November of 2010, and the winter of 2011 was still used for supervised testing of the repeater at the QTH of Rolf, DL2ARH.
The repeater rack was finally installed in its final location on 26.03.2011, shortly after internet connectivity to the site had been established. With support from Torsten DL4APJ, Rolf DL2ARH, Winfried DL2AWT, Sebastian DL3YC and Stefan DK3SB, the repeater could be installed and brought to live in its new home. Essentially all hardware installed in 2011 is still operating at the site today. Some aspects of the software have changed together with the rapidly evolving D-Star ecosystem. These days, the repeater is connected to the ircDDB network, which takes care of routing. The xReflector system superseded the D-Plus reflectors previously used.
With a significant reduction of amateur television operators, fueled by the continued lack of two-way video links, the 10 GHz frequencies formerly used for this mode of operation fell out of use. The excellent location of the repeater site offered the opportunity of installing SHF beacons. Initial prototyping of a beacon transmitter started in Winter 2020. A first prototype was built and tested in early 2021, and an improved version assembled later that year. The final beacon transmitter hardware was provided to Rolf, DL2ARH in Winter of 2021, who manufactured the weather-proof outdoor housing, mounting facilities as well as the indoor rack unit from individual components. A slot antenna from the old ATV equipment was salvaged and re-tuned to the newly coordinated beacon frequency. A first test period during early 2022 demonstrated that the beacon operated correctly. Installation of the outdoor unit on the rooftop of DB0HDF was performed in April 2022.