The ZL Hellschreiber Beacon Project

IARU Logo With the sunspot peak passing and radio propagation slowly falling off on the higher bands over the next few years, there will be heightened interest by Amateur Radio operators in the lower bands. These amateurs need to know what propation exists at various radio frequencies at different times of the day. A family of excellent HF beacons has been set up by the IARU & NCDXF, which allow study of propagation on the bands from 20m upwards, but there are few beacons on the lower bands. The lower bands require special consideration. IARU Logo

The higher bands are quiet, and signals are there, or they are not, as conditions dictate. The lower bands are much more noisy, and signals are present for much of the time, but are often buried in noise or signals from other parts of the world. The propagation mechanisms are much more complex, requiring a different beacon strategy for these frequencies.

This web site describes a low power beacon system to be used for propagation and performance tests on the lower bands. The beacon offers CW (on-off keyed) modes and FSK modes; the traditional Morse ID mode, and Feld-Hell, another highly noise immune CW mode. As development of beacon keyers progresses other modes such as RTTY, MFSK and PSK31 will be included. Hell, MFSK16 and PSK31 are also very sensitive modes and ideal for this application. You can read about Feld-Hell, MFSK16 and PSK31 on their own web sites.

Of course the different modes to be transmitted by the beacon mean that Amateurs will have the opportunity to compare the relative performance of different modes under changing conditions.

The transmitter, which covers 160m to 20m, is a converted commercial unit, adapted to Amateur bands. The keyer is complete and operating, with a temporary DDS VFO providing operation on 160, 80, 40 and 30m.

A more intelligent computer controlled DDS VFO with bandswitching is in the development pipeline. The work is being undertaken by ZL1BPU when time permits, although assistance and donations toward the project have been made, and more would be very welcome. The beacon was first in action in August 1999, but operation has been sporadic (essentially on request) due to lack of a permanent site and lack of VFO memory (there is no battery backup at present).

It is hoped to operate at about 20W output on the 40m band, 24 hours/day, and other bands on request. Dual-band or multi-band operation is not contemplated with the present rig. Power level switching is practical with the new keyer. Further suggestions are welcome. Other modes are possible using a PC keyer.

How you can help: - Make a suggestion, donation or offer of assistance

Donations (money, equipment) toward the project would be very welcome. In particular, multi-band operation will require a remote-switched rig with multiple memories (e.g. a Kenwood TS50). Offers to construct and manage similar beacons in other countries would also be welcome. Obviously offers of practical assistance are best from within ZL. Grateful thanks to those who have already contributed to the project.

The Keyer

 
Designer:     ZL1BPU
Software:     ZL1BPU (written in AVR Assembler)
Construction: Prototype on spot board, 100 mm x 100 mm x 20 mm
Status:       Operating Nov 2000 (previous beacon operation used a PC keyer)
The keyer is a multi-mode unit, sending Feld-Hell or Morse using ASK or FSK. It will send both "standard" and "DX mode" Feld-Hell, at the standard 122.5 bits/second, as the following example shows:

The keyer is very versatile, and was designed so that at a later date we can run other experiments using other techniques and modes. As can be seen in the picture above, the keyer also sends telemetry giving data about the transmitter, power supply and antenna. It will also send the telemetry message via a packet terminal if necessary.

The keyer is based on an AVR AT90S4433 RISC processor running at 4 MHz. The message is in EEPROM and easily changed with an ASCII terminal. Any mixture of Hell and Morse is possible, at several speeds and with embedded mode commands, control commands and telemetry messages. The font used is the ZL1BPU MOSAIC II 7 x 5 font. See the Keyer Page

The Transceiver

 
Designer:     Codan, ZL1BPU
Model:        6801S Mk2B (24V marine)
Donated:      ZL2TFK
Conversion:   ZL1BPU
Software:     Still to be designed
Status:       Transceiver tuned up all bands May 99
The transceiver is a converted commercial HF radio-telephone, donated by Colin ZL2TFK. The unit is a Codan 6801S Mk 2B. This is a 120W 24V marine transceiver dating from the early '80s, very simple in concept, rugged and reliable. In the original configuration the unit has 10 crystal controlled channels, on any frequency from 1.8 MHz to 16 MHz, true AM or Upper Sideband.

The transceiver is single conversion with an IF of 1650 kHz. This necessitates a good preselector (Q of about 25) for each channel to ensure suppression of the image frequency. Ten preselectors are provided, one for each channel. These 10 channels have been set to provide coverage of five Amateur bands, in segments where necessary:

Where it all started
The Codan 6801S - as is, where is!

  1. 160m 1.8 - 1.85 MHz
  2. 80m 3.50 - 3.60 MHz
  3. 80m 3.60 - 3.70 MHz
  4. 80m 3.70 - 3.80 MHz
  5. 80m 3.80 - 3.90 MHz
  6. Unassigned (about 5 MHz)
  7. Unassigned (about 6 MHz)
  8. 40m 7.00 - 7.20 MHz
  9. 30m 10.0 - 10.3 MHz
  10. 20m 14.0 - 15.0 MHz
Notice that the coverage allows reception of WWV at 5, 10 and 15 MHz. The intention of the transceiver conversion is to provide a useful general coverage transceiver, not just a beacon transmitter, although the gain and power output will be reduced outside the ranges quoted above, and the image suppression may be poor. For full details of the transceiver conversion, see the Transceiver Project page.

Frequency Control

Initial operation was crystal controlled. The crystals were 30pF load 25°C HC6U holder, 1650.0 kHz above the operating suppressed carrier frequency (USB), or below the suppressed carrier frequency (LSB). The output tone frequency (i.e. the CW/Hell carrier) will be 980 Hz higher (USB) or 980 Hz lower (LSB).

To allow such a wide range of coverage, a very wide range very stable VFO is required for the first mixer. For upper sideband, the VFO runs above the receive frequency, so a range of 3.45 MHz to 16.65 MHz is required. For lower sideband, the signal is inverted by running the VFO below the receive frequency, so a range of 0.15 to 13.35 MHz is necessary. (Image rejection may be poor on the 160m band in LSB mode, since the image is only 300 kHz away).

The obvious answer to the VFO requirement is to use a Direct Digital Synthesizer. A DDS VFO is under way, thanks to Steve KD1JV.

At present one of Steve's little 0 - 9 MHz DDS VFOs is used, and will be replaced by a more intelligent higher performance unit based on an Analog Devices AD7008 50 MHz device, capable of providing a clean VFO signal to 16 MHz. New software will be written for an AVR micro, permitting the VFO frequency to track the bandswitch and operating sideband, and potentially allow keyer-controlled bandswitching.

For full details of the DDS VFO project as it progresses, see the DDS VFO Project page.

Power Supply

Designer:     Standard Power Inc
Model:        SPS/CPS 120-24 (24V 6A nominal)
Status:       Operational May 99 - needs case, connections and fuses. No battery backup.
The power supply requirements of a 24V transceiver are modest, but of a continuous duty nature when operating the beacon. An open-frame commercial power supply of industrial origin has been selected for the project. This unit, made by Standard Power Inc, provides 24V regulated at 6A continuous. It employs three 2N3055 transistors on a huge heatsink. A case, connectors and such essentials as a line fuse and output fuse are yet to be organised. No back-up battery is planned, so the VFO and Keyer controllers will need to have their own backup. bare bones power supply

Antenna and Site

Designer:     ZL1BPU
Construction: TBD
Status:       Not started - parts being collected
A simple pair of inverted Vee dipoles with the apex at about 6m, supported by a single steel mast is planned. The dipoles (initially for 30m and 40m) will be mounted at right-angles and fed from a common RG58 coaxial feeder. A ferrite ring brute force balun constructed on the mast-head end of the coax will provide balanced feed. The antennas will also act as guys to support the galvanised steel mast, which will be dropped into a stump of larger pipe post-rammed into the ground.

The antenna will provide radiation at all angles, allowing local and DX reception, allowing the opportunity for mixed path reception experiments.

Antenna diagram

The project needs a rural site in South Auckland, with 230V AC power, reasonable security for the equipment and reasonable access. Preferably a farm shed or other building with space around it for the antenna.