{"id":689,"date":"2026-03-23T14:50:25","date_gmt":"2026-03-23T13:50:25","guid":{"rendered":"https:\/\/www.i8zse.it\/en\/?page_id=689"},"modified":"2026-03-23T15:15:12","modified_gmt":"2026-03-23T14:15:12","slug":"power-supply","status":"publish","type":"page","link":"https:\/\/www.i8zse.it\/en\/radio\/power-supply\/","title":{"rendered":"Power supply"},"content":{"rendered":"

Modern equipment, except for rare cases, is all powered at 12V, so to operate from the mains it requires a power supply. In addition, since multiple low\u2011voltage devices are normally used in the shack<\/em>1<\/a><\/sup>, it is also useful to think about a low\u2011voltage distribution line.<\/p>\n

How to proceed? The nominal voltage of the devices is usually 13.5V, suitable for use in vehicles. In general, the acceptable voltage range is wider, but it is always good practice to check the device manual<\/strong> to know the allowed voltages. The specifications also indicate the current consumption, which is the other important element for properly sizing the power system. As a rule of thumb, QRP devices draw less than 5A, while 100W radios reach 20A. The power supply must provide the nominal voltage with a current equal to or greater than the maximum consumption of the device (or devices) being powered.<\/p>\n

The choice of the right model must start from a few basic considerations.<\/p>\n

Power supplies<\/h2>\n

Power supplies can be grouped into two major families.<\/p>\n

The first is that of linear power supplies<\/strong>. The mains voltage is reduced by a low\u2011frequency transformer (50 Hz in Europe) and brought to a voltage slightly higher than required. This AC voltage is first rectified and filtered, becoming DC but not stabilized. The regulation circuit operates through one or more transistors\u2014or integrated circuits\u2014that act as a sort of variable resistor, continuously and linearly adjusting their conductivity to keep the output voltage stable. If well designed, this type has low output impedance and virtually no noise. The downside lies in the size of the components, mainly the transformer and heat sinks, since the regulation dissipates as heat the energy contained in the difference between the unregulated voltage and the output voltage for the required current. This also affects the efficiency of the power supply, which is relatively low.<\/p>\n

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The second family is that of switching power supplies<\/strong>. In these, the mains voltage is rectified and filtered directly, and then switched at high frequency<\/strong> by one or more transistors driven by a square wave at tens or hundreds of kHz. A square wave can be thought of as two states: in the first (0) the transistor does not conduct, in the second (1) it conducts. The regulation circuit measures the output voltage and adjusts the ratio between the duration of the two states: the longer the \u201c1\u201d state, the higher the output voltage. This voltage is passed through a high\u2011frequency transformer, much smaller and lighter than a low\u2011frequency one, and then rectified and filtered. The advantages are high efficiency, reduced size and weight. The downside is that switching generates noise and harmonics which, if not properly filtered and suppressed, can cause interference both in radio frequencies and in audio.<\/p>\n

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In recent years the trend has clearly shifted toward switching power supplies, but in amateur radio use it is important to consider the RF noise generated by the power supply. If the EMI filters of switching supplies are well designed, problems are rare. If they are poorly designed\u2014or even absent, as often happens with LED power supplies\u2014the power supply behaves like a broadband noise source, and the power cable like an antenna. Consider that an ideal square wave has an infinite series of harmonics; in reality, rise and fall times are never instantaneous, which limits the effective bandwidth, but a poorly built switching supply can create dramatic effects and make some bands\u2014especially the lower ones\u2014completely unusable.<\/p>\n

The noise level of a power supply is easy to check, even with a simple AM radio.<\/p>\n

For some services that handle very weak signals, such as antenna preamplifiers, it is advisable to avoid switching power supplies altogether\u2014given the low currents involved\u2014and prefer linear supplies with excellent filtering.<\/p>\n

Connectors<\/h2>\n

While nothing prevents you from connecting devices directly to the power source without connectors, my suggestion is to avoid this approach and always<\/strong> use polarized connectors<\/strong>. This is not a whim: it is a matter of reliability<\/strong>, safety<\/strong>, and operational continuity<\/strong>.<\/p>\n

The first goal is to avoid polarity reversal<\/strong>, an error that is the most common cause of equipment failure. If the device is not protected\u2014and not all devices are\u2014you risk seriously damaging valuable equipment. With a non\u2011polarized connector<\/strong> (single fastons, banana plugs, loose terminals, improvised jacks), it is simply too easy<\/em> to make a mistake in a moment of haste, darkness, rain, contest, field day, etc. Mechanical polarization<\/strong> ensures that an incorrect insertion is physically impossible.<\/p>\n

The second goal is to reduce errors, which are always possible when in a hurry or when multiple people handle the same equipment. In amateur radio, work is often done in civil protection groups, contests, field days, expeditions, shared installations. With polarized connectors, you can operate without worrying.<\/p>\n

The third goal is compatibility between different devices: rarely does the power cable of one device fit another, but if you use the same polarized connectors, you can connect any device to any power source safely.<\/p>\n

This is why in radio it has always been essential to use polarized connectors<\/strong> for all power lines, especially those above 5\u201310 A. Human error is inevitable<\/strong>, so the connector must physically prevent the mistake. You don\u2019t need an expert \u201cbeing careful\u201d: you need a system that does not allow<\/em> mistakes. XT60, Powerpole, Anderson SB, Molex Mini\u2011Fit, etc.\u2014anything polarized<\/em> is a major improvement over improvised solutions.<\/p>\n

Powerpole<\/strong><\/h2>\n

In the amateur world, the Anderson PP15\/30\/45 Powerpole connector has become very popular.<\/p>\n

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Today it has become almost a de facto standard<\/strong> for 12\u201313.8 V DC. It has many advantages:<\/p>\n