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FS-5000 TX

The transmitter is the core-component of the FS-5000 radio set. In a completely assembled radio station, al signals and power lines are routed through the transmitter. It is normally used in combination with the Automatic Antenna Tuner that is stacked on top of the transmitter. In a complete FS-5000 radio station, the assembly of transmitter and antenna tuner is located at the rear left. The transmitter is suitable for frequencies between 1.6 and 30 MHz, controlled by DSU and receiver, in 1 kHz steps. It uses VSB-modulation for the transmission of digital signals.

The image on the right shows a typical FS-5000 transmitter. It has connectors on three sides. At the right is the connection to the PSU/Charger. In some countries this socket is blocked by a plastic blanking plate, to avoid EMC-problems.

At the front are two connectors for the batteries (left) and one large socket (right) that accepts the receiver. This socket contains a number of coax connectors that carry the antenna signal to the receiver and the modulated data from the DSU to the transmitter. All connectors carry data lines for communication between the modules.

At the top surface (left) is the socket for the antenna tuner that is normally mounted on top of the transmitter. The tuner has a plug that mates with this socket. It is possible to use the transmitter stand-alone (i.e. without the antenna tuner) with aid of the X-unit, albeit with a much reduced output power in order to avoid damage resulting from mis-matching.

Transmitter Transmitter and Antenna Tuner stacked together Transmitter with shielded power input connector Power input connector on the transmitter Complete FS-5000 radio station

Technical description
The transmitter consists of two stacked modules: the actual transmitter (TX) and the automatic antenna tuner (ATU) on top of it. The transmitter is tuned by the receiver under control of the DSU. The receiver's synthesizer generates the necessary signals from a 10MHz TCXO: a variable 52-80MHz signal (tuning), 50MHz (IF) and 200kHz for the VSB-modulator (see below).

Transmitter block diagram

The (frequency) control signals from the DSU are used by the transmitter to select the apropriate band-pass filter in the PA output stage. The antenna tuner has its own CPU to allow fully automatic matching of the connected (wire) antenna. It provides a feedback signal to the transmitter to allow the output power to be reduced in case of a bad VSWR.

VSB Modulation
For the transmission of message bursts, the FS-5000 uses a very sophisticated modulation technique, called Vestigial Side Band Modulation (VSB or C1D), compatible with ECHOTEL. This allows the transmitter to send a message over a channel with an extremely narrow bandwidth at a speed of 2000 baud. As a result, sending a 55 character message takes no more than 0.8 sec. [10], making Direction Finding (DF) practically impossible! The principle is explained in a number of US patents that were filed around this time [6] [7] [8].

Much of this circuit is directly visible when observing the left half of the upper PCB of the transmitter (see below). The two PROMs are each 8KB deep and contain a high-resolution sine-wave table, which is necessary to obtain sufficient spectral purity of the output signal [9]. Please note that the receiver uses a different kind of modulation (SSB) with much lower speed (75 baud).

The transmitter has two compartments that are separated by a 'floor'. Each compartment contains a large PCB; one at the top and one at the bottom. The transmitter is extremely well-built with a keen eye for detail and it is clear that money was no object when the FS-5000 was designed.

The PCBs inside the transmitter can be accessed by removing the top and bottom panels. The image on the right shows the top board.

The right half of the top board is filled with a series of high-performance Avantek GPD-series HF amplifiers [5] and MCL filters and mixers.

The left half is filled with ICs that form an I&Q modulator. The SIN and COS signals are each produced by a TBP28L22 8KB PROM [2] followed by an AD7524 Multiplying 8-bit DAC [3] and SE5514 high-performance OpAmps [4].
Transmitter interior (top board)

The I&Q modulator gets a 200 kHz reference signal from the receiver and is the heart of the VSB-modulation used by the FS-5000. The transmitter does not contain a frequency synthesizer. Instead the transmission frequency is determined by the receiver and is delivered via the large connector (front) in the form of a 2-30 MHz signal and a 50 MHz signal.

The bottom section of the transmitter contains the HF pre-amplifier, based on an MRF134 (or DV1202), and the Power Amplifier (PA) with an ON4347, followed by several band-pass filters.

As the transmitter covers a very wide frequency range (2-30 MHz) different band-pass filters are used for each frequency band. Nine relays are used to select the appropriate filter and a tiny LED-array shows which filter is activated.

Also on this board the HF-relay that connects the antenna to the transmitter or to the receiver.
Transmitter interior (bottom board)

Several teflon coax cables (and other signal lines) connect the two boards together and to the connectors at the front (receiver) and at the top (antenna tuner).

Transmitter top board Transmitter interior (top board) Transmitter bottom board Transmitter interior (bottom board) Transmitter Power Amplifier (PA) TX output harmonic filters

Technical specifications
  • Frequency range: 2-30MHz
  • Step size: 1kHz
  • Antenna length: 7.5-25 meter (long-wire)
  • Output power: 30W
  • Output from ATU: > 15W (typical)
  • Output during tuning: < 5mW
  • Tuning time: < 3s (typical < 1s)
  • Current: 8A (during TX)
  • Harmonic suppression: 50dB
  • Modulation: VSB (C1D), compatible with ECHOTEL
  • Transmission speed: 2000 baud
  • Message duration: < 0.8s
  1. Helmut 'Jim' Meyer, HS0ZHK, My way to Ham - Radio and beyond
    Website QRZ.COM. Personal correspondence. Retrieved June 2008.

  2. Texas Instruments (TI), TBP28L22 Programmable Low-power ROM
    8KB PROM. 1985. Retrieved April 2012.

  3. Analog Devices, AD7524 CMOS 8-bit Buffered Multiplying DAC
    Rev. B, November 1986. Retrieved April 2012.

  4. Philips Semiconductor, NE/SE5514 Quad high-performance OpAmp
    31 August 1994. Retrieved April 2012.

  5. Avantek, GPD Series, High-performance IF/HF Amplifiers
    Date unknown. Retrieved April 2012.

  6. United States patent 4,780,884, Suppressed Double-Sideband Communication System
    Filed 13 April 1987. Approved 25 October 1988. Previously filed as 741,026 (3 June 1985) and 835,265 (3 March 1986), both abandonned. Retrieved April 2012.

  7. United States Patent 4,730,345, Vestigial Sideband Signal Decoder
    Filed 4 April 1986. Approved 8 March 1988. Retrieved April 2012.

  8. United States Patent 5,663,773, Demodulator for a Complex-Value VSB Signal
    Filed 20 November 1995 on behalf of ANT Nachrichtentechnik GmbH, Backnang (Germany). Approved 2 September 1997. Retrieved April 2012.

  9. Prof. Dr.-Ing. Dietmar Rudolph, Einseitenband & Restseitenband Modulation
    TFH Berlin - Telekom TT - IBH. (German) Date unknown. Retrieved April 2012.

  10. Dipl.- Ing. Roland Prösch, Technical Handbook for Radio Monitoring I
    2007. ISBN 9783833490156.
    ECHOTEL 1810 HF-modem, pp.148-150.
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