Surveillance Spy Bug Transmitter
Powerful - Stable - Small

Range Tests

In order to see how far the Long Ranger™ transmitter would reach it was connected to four AAA batteries (6 volts) and two antenna radials were utilized, one connected to the antenna terminal and the other to the circuit board ground, see the two black wiresin the photo.
Each wire was cut to a quarter wavelength at the operating frequency which in our tests was 107.9 MHz. At this frequency each wire radial is 69.5 cm or just over 27 inches. The overall length of this half wave dipole is 1.4 m or 54 inches.

Dipole Antenna

It's better to feed the half wave antenna in the middle because there is a good match to the low impedance output of the transmitter. It is possible to feed a half wave antenna at the end but it's a very poor match to most transmitters unless extra measuresare taken to match the impedance.
Without impedance matching the end result is reduced radiated signal.
It could also be argued that a balun should be used here due to the antenna being a balanced feed and the output of the transmitter being unbalanced but since there is no transmission line feeder we kept it simple.

The transmitter was strapped to a wooden mast and the antenna radials were secured along the mast. An MP3 player connected to the transmitter produced the audio. This is visible in the photo.
The whole unit was placed on a hill so that the antenna orientation would be vertical as you can see in the photo.

We drove away from the hill using a standard digitally tuned car radio and achieved a distance of 15 miles (25 Km) before the signal started getting scratchy or noisey.
The reception was solid all the way to that point. Since the hill could no longer be seen clearly due to obstructions it's possible that a greater distance could be achieved if the transmitter was within line of sight.

This is truly remarkable for such a low powered transmitter and proves what can be achieved with a clean signal that is exactly on frequency.

The receiver used also has a bearing on the distance possible. More range tests are planned using a more sensitive receiver and more suitable location such as between two mountain tops or skyscrapers.

Please let us know your experiences. We would welcome any feedback regarding range achieved using this transmitter's standard configuration.
It's possible to boost the power of the transmitter by lowering the value of a resistor on the circuit board but that would be less fun.

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