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Tech Note: Overheating

Even if the summer heat has passed, the heat dissipated by a 35 Watt radio can be an issue any time of year. It is perfectly normal for a 35W transmitter to generate enough heat to be very uncomfortable to the touch. Any transmitter of any major brand consumes energy equal to about three times the radiated power. In the case of a 35W transmitter, that is about 105 Watts. As a comparison, a 100 Watt light bulb cannot be touched when it is on because it is too hot to be handled. Something similar happens to a radio, although there are various steps you can take to decrease this large amount of heat.

The first precaution the manufacturer takes is that a radio of 35W power is equipped with a heat-sink. Note that the heat-sink, normally mounted on the back of the unit, is only effective if air circulates freely without obstructions, and circulates vertically. A radio mounted horizontally will heat up much more than one whose flow of air can freely flow from bottom to top.

A potential source of overheating can be in RTK equipment working with multiple constellations, thus requiring longer strings of data to be transmitted each second. This means that the transmitter will stay on for a longer period of time, generating more heat. The solution is a higher over-the-air speed, which will in turn reduce the transmission time. For example, a base radio sending RTK corrections to a rover utilizing a GMSK protocol will generate almost twice as much heat as a base radio using a faster protocol like 4FSK (at the same bandwidth). The difference can be dramatic.

Another undesirable source of heat is the so-called “reflected power”. All the RF power of the radio should reach the antenna and should be radiated in the form of electromagnetic energy. If some of it returns back to the radio, the radio will heat up considerably more, not to mention that the working range will be reduced. In order to prevent reflected power, it’s very important to use a good RF cable with no damage and to make sure that the antenna is in good working condition without connector oxidation or other visible damage. Also, many users who utilize a steel whip antenna may not be aware that this type of antenna requires “tuning” to the right operating frequency. Normally such antennas are sold at a length which is optimal for the lowest frequency of its range. When a higher frequency is used, the operator should then cut it to the right length, as listed in the antenna instructions. Many users disregard this “fine tuning”, thus somewhat reducing their working range and increasing the heat (however only marginally).

Even if all the above is taken care of, when a radio is left operating in full sunshine on a hot day, it will inevitably heat up. SATEL radios have an internal protection that prevents damage once the radio reaches 176°F (80°C). The radio will continue to operate at reduced power, and the screen will flash to alert the operator.

Your best course of action if you believe heat has become a problem, especially in the summer or in warmer regions: reduce the power of the transmitter from 35W to 25W. It may be counter-intuitive, but this reduction of power (about 30%) will not affect the range very much. In fact, the range will decrease by about 15%, with the potential of saving you from a lot of downtime.