Getting Started

Interested in IARU style ARDF but have no equipment?

ON7YD 80m micro transmitter

A micro power transmitter for 80m or 2m is an ideal starting point for your ARDF experience, simple enough to build on prototype board, for those with basic homebrew skills. Powered by a 9v PP3 battery, it provides a useful signal source when building receivers, and can be used for short-range ARDF.

The micro transmitters schematics are reproduced from the web site of ON7YD
Full details can be found at https://www.qsl.net/on7yd/ardfbrew.htm

Provides continuous keyed CW ( code T, repeated )

Notes and variations to the original.

• C9 - found to be necessary to get xtal to start reliably.
• D1 - added for reverse polarity protection.
• K2 - optional power switch.
• L1 - T50/T37-2 or T50/T37-6 toroid
• IC1- NOTE: Some CD4001 variants may not be suitable or give low output. (HEF4001BP used and verified ok.)

ON7YD 2m micro transmitter

Provides pseudo- AM/FM modulation.

Notes

• X1 is a standard 24MHz xtal, but made to oscillate on its 3rd overtone. The overtone frequency will be slightly above 72MHz, so when doubled in the collector tuned circuit L2, the output frequency will be about 144.070MHz. Using a xtal designed for series operation will raise the output frequency to about 144.170Mhz.

• T1 other suitable transistors ; hfe >20 & fT >400MHz

A Super Simple 80m Reciever

This receiver was designed and used by Tony Green GW4JGU

Notes

• X1: Only use a crystal, not a ceramic resonator (there is no voltage regulation).
• L1: The turns ratio is selected for useable gain not maximum gain, when hunting classic higher power transmitters (3-5w).
  10:2 is suggested for a loop antenna.
  10:4 is suggested for a ferrite rod antenna.
  10:10 for maximum gain.
• A advanced version of this design is described elsewhere on this web site, adding battery switching, variable gain, and full tuning across the 80m ARDF band. You can also find a description of suitable antennas.

2m AM receiver

An original 1989 design by OK2BWN was the basis for the ROX2T by G3ZOI (shown below). This uses the volume of the rectified keyed modulation (or speech) to determine the signal strength so is only suitable for receiving AM.
(the ROX-2K could be used for AM/FM)

The ROX-2T just uses two RF ICs. The SA612 + TA7613. Even though the major components are now obsolete, including both ICs and the filter, it should be possible to source these components for a one-off build.
The SA612 will provide an suitably stable high frequency VFO. The AM mode, together with the relatively wide ceramic filter will mitigate against the effects of VFO drift.
Full details of this receiver can be found elsewhere on this website.