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The Beginning of Practical Amateur Radio Radiolocation

Created by on 2023-07-30

One of the areas of the FMT project   involves research and experiments in the field of radarization using amateur radio equipment at short-wave frequencies. At this point in the summer of 2023, successful measurements have already been made to determine distances at intercontinental ranges, from the results of which we can all start further research. The first amateur radio operators who proved in practice the possibility of such accurate measurements were: UA9LIF, W6DSR, WA2DVU, SP5LST.

However, the determination of distances is not an end in itself, as it is of little practical use. For a motivated amateur radio researcher it is more interesting the measurement process itself, which leads to a better result each time. New methods and tools used for this purpose are important, exchange of experience of participants is interesting.

There are old proven methods based on competition to motivate to make such measurements. These are classical contests and competitions.

In order to be able to organize such contests a methodology was developed and a measuring signal was created, which is emitted in beacon mode on known frequencies.

Practical measurement of such a signal from the air is available to every radio amateur.

It is very important to realize that the accuracy of the signals emitted by FMT transmitter will be many orders of magnitude higher than the results of the measurements obtained, due to the imposed limitations of natural constraints such as fading or Doppler shifts. Because of this, there is a very large field of activity on how to overcome these limitations and improve the results of one's on-air measurements in spite of the instability of the ionosphere. How is it possible to approach absolute accuracy of the radiated signals and how to do it? Who will come up with the best way and win the contest?

Let's look at the possibilities of a reference signal that helps to overcome such problems.

This precision signal is two pulses of 50 msec each, with a pause of 50 msec between them. The front of the first pulse of the FMTBeacon transmitter is strictly tied to UTC global time and acts as the starting point.

Knowing in advance the exact parameters of these two pulses, manipulating oscilloscope markers, it is possible to achieve accuracy of on-air measurements in the range of tenths of milliseconds or better.

Oscillogram (green) of the beacon signal received in Europe. Distance from the transmitter ~ 8000 km. Three measuring pulses and their time shift relative to the signal 1 PPS (yellow oscillogram) are clearly visible.

Thus, receiving the beacon signal, we will see on the oscilloscope screen some delay-offset relative to the local pulse 1PPSu of the meter, which arises due to the presence of the effect of its delay during propagation through the air. This delay will depend directly on the distance between the receiver and transmitter. Each meter will have a different delay because the receivers are in different locations.

So how can we make the conditions of the contest so that with different distances between the participants, there is a possibility of determining a single constant that must be correctly determined?

For this purpose, only during the competition, a special delay for pulses is introduced into the reference beacon signal, which is called "Delay test". It is this delay that you will have to report as the result of your measurements.

Delay "Delay test" can be correctly determined only by preliminarily calibrating your amateur radio receiving and measuring equipment to the reference signals.

The calibration of your receivers is done using the reference beacon signals before the contest. During these days you will need to adjust your equipment so that the correct distance to the transmitter, expressed in milliseconds, is accurately recorded on the screen of your oscilloscope.

When you are sure of the accuracy of your measurements on the reference beacon signal, you will be able to calculate the unknown "Delay test" delay, which was introduced into the beacon signal during the competition.

The methods of determining the distances to the transmitter, photos and videos, description of the beacon operation can be found directly on the website of the FMT beacon project.

In September the next contest FMT-7 will be held, in which you will be able to discover a new technical direction - amateur radar.

When summarizing the results of the contests, record tables with the best results of the participants are compiled.

Extensive material, devoted to problems connected with signal delays arising in receiving devices, will be published soon.

See you on the air and 73!

Alex RU0LL