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Here, we show you all our modem models from the beginning.

The History

Two German hams DF4KV and DL6MAA initiated the PACTOR project. As early as 1986, experiments with modified AMTOR protocols began. In tedious tests, the noise conditions on the HF-Bands were investigated, and the best transmission parameters were determined. Additionally, a lot of mathematical calculations were performed, the PACTOR protocol deduced from these results. The first PTC's were wire-wrapped on bread-boards. DL6MAA built his PTC based on a SMD Z80 single-chip processor, while DF4KV wire-wrapped his PTC in conventional Z80 technology.


PTC-I UR PTC alias Peter Helfert Z80
The first PTC

PTC-I UR PTC alias Peter Helfert Z80

Hans Peter Helfert development the first rea working PTC-I Modem based on the Z-80 processor with PACTOR 1 software revision.

The third station that got on the air in PACTOR was DL2FAK. His PTC was based on DL6MAA's SMD Z80 version. DL2FAK and DL6MAA ran a lot of tests that resulted in considerable improvements to PACTOR. In the fall of 1989 he developed a PT-link system that facilitated access to Packet-Radio nets from PACTOR. Since the SMD based PTC of DL6MAA was too difficult for home construction (SMD), and DF4KV's version contained too many parts, it was decided to develop a completely new hardware design. DL3FCJ developed the digital section of this hardware, DL6MAA developing the modem, and carried out software adjustments. The software was rounded out with inclusion of an RTTY and AMTOR routine from DK4FV. DL1ZAM revised the circuit diagram and produced the printed-circuit-board layout, and so the well known SCS-PTC came about, and quickly covered the globe.

PTC-I Series Model

The PTC-I Model in series


In 1993 the production of the Z80-STI peripherial chip, used in the Z80 PTC, ended. This was then the opportunity to develop the PTCplus. Based on an MC68000 processor, the PTCplus is the springboard to a totally new dimension in modern HF communications.

PTC-plus series model

The PTC plus in series

Together with the PTCplus, the development of the PTC-II was also undertaken. The PTC-II project required a thorough knowledge of signal processing technology and it´s associated programming. Much research work was necessary to develop the present PACTOR-II modulation process. Despite all this, it was possible to astonish visitors to the 1994 HAM-Radio convention with the first prototype PTC-II.

PTC-II Prototyp 1 PCB Bottom View

First PCB Layout

PTC-II Serie Model

The PTC-II under test

PTC-II Serie Model

The PTC-II in series


In summer of 1999 the “small brother” of the PTC-II, the PTC-IIe was ready for sale. Being less expensive at excellent performance and the increasing need of email via HF made the PTC-IIe to be THE standard modem for HF-email within a short time.

PTC-IIe series model

The PTC-IIe in series


Sommer 2001 the PTC-IIpro followed. As successor of the PTC-II, the PTC-IIpro now establishes the new top of SCS’s goal to provide the best modem-technology for data transmission via HF at all.

PTC-IIpro serie model

The PTC-IIpro in series

At the first of May 2002 SCS introduced the new developed high speed data mode PACTOR-III. PACTOR-III is a third generation HF protocol building on latest developments in 2-dimensional orthogonal pulse shaping, advanced error control coding, and efficient source coding. Due to the advanced signal processing methods applied, PACTOR-III provides outstanding performance under poor and moderate signal conditions. As PACTOR-III also achieves very high throughput rates under good signal conditions, it is well-suited to HF channels with good SNR and low signal distortion as well. During the development of PACTOR-III, high importance was attached to compatibility with ordinary SSB transceivers (using standard 2.2-2.4 kHz wide IF-filters). Therefore, PACTOR-III can achieve its maximum speed with using unmodified, common SSB transceivers. The occupied bandwidth is around 2200 Hz. Thus PACTOR-III is the ideal means of fast and reliable data communication over (the sometimes difficult medium) HF-radio. The new protocol is fully backwards compatible to existing PACTOR-I/II networks.


In summer 2003 the PTC-IIex suceeded the PTC-IIe. Although both models nearls not differ from their outer appearance, in the inside the PTC-IIex has been deeply reworked. The PTC-IIex comes with a more powerful DSP section, a TXCO stabilized oscillator, a better power supply and with 2 MB of static RAM. 

PTC-IIex series model

The PTC-IIex


As an answer to the increasing demand for a modem with USB connection, SCS introduced the PTC-IIusb in the mid of 2005.

PTC-IIusb series model

The PTC-IIusb

The ease the use of the PACTOR-IP-Bridge, the same time SCS introduced the PTC-IInet. This unit is a neat combination of a HF radio modem with a miniature Linux computer with Ethernet connection, all fitting inside the modem enclosure itself.

PTC-IInet series model

 The PTC-net

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