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I am a new General and don't quite understand how Antenna Tuners work other than changing the impedance ratio between the radio and the antenna.

So my question is -

Do I need to buy a new tuner if I buy an HF amp ? I have a Elecract HF rig that has a built in tuner (rated at 20W). I want to purchase the Hardrock-50 HF amp. I don't think the Elecraft's tuner will tune through the 50 watt amp to the antenna ? Need some advice. Thanks. 73

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  • $\begingroup$ Buying a 50 watt amp for a 20 watt HF rig is not going to give you a big advantage. A 100 watt amp makes more sense and Elecraft makes 100 watt amps fitting for each of their HF rigs. I know it is more money but I suggest waiting on the amp and take that 20 watts out for a drive. If you consider digital modes (e.g. PSK and others) then that 20 watts is a good signal level. I operate QRP CW quite a bit at 5 watts and although you are not going to peak someone's S-meter, you will be heard, it just takes a little more effort. $\endgroup$
    – K7PEH
    Commented Dec 8, 2016 at 16:22
  • $\begingroup$ The radio doesn't broadcast at 20 watts, that's just the limit of the ATU. The radio does a max of 12 watts. Also I want to get experience by building the kit. $\endgroup$
    – Khris Kramer
    Commented Dec 8, 2016 at 19:00
  • $\begingroup$ -- sounds like an Elecraft KX3. I have one. Note that with firmware revision 2.38 the maximum power out is now 15 watts for bands 80 to 20 meters. I never use an amp with my KX3. Well, small correction, I once fed my KPA500 500-watt amp with my KX3 to get about 180 watts output but that was an experiment. $\endgroup$
    – K7PEH
    Commented Dec 8, 2016 at 20:58
  • $\begingroup$ As noted you need an antenna tuner between the amplifier and the antenna. If I was buying a Hardrock-50 to go with my Elecraft KX3 (which I am also considering :-), I would also spring for the antenna tuner that can be built into the amp, the HARDROCK-50 ATU Kit link. 73. $\endgroup$
    – Malcolm VE2DDZ
    Commented Dec 13, 2016 at 12:59

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Yes, you'll need an external tuner, unless your antenna is already matched sufficiently well to 50 ohms. The objective of the tuner is to transform the impedance seen by some signal source, like your radio, or the amplifier.

The amplifier will already be designed to have a 50 ohm input. Your radio, transmitting into that, is designed for a 50 ohm output, so there's no need for a tuner.

The amplifier will see your antenna impedance though the feedline, whatever that is. The amplifier is also designed for a 50 ohm load. If your antenna is sufficiently close to 50 ohms, then no tuner is necessary. Otherwise, you'll need a tuner somewhere between the antenna and the amplifier, since the radio's tuner will have no effect on the impedance seen by the amplifier.

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Your antenna tuner should live between whatever final amplifier you are using and the antenna. The internal ATU in your radio becomes moot when you add an external amplifier, and should not be used. Whatever amplifier you are using will have a 50-ohm input that matches the output of your transceiver.

The tuning network of your amplifier is already capable of matching a slight mismatch. It is after all a matching network. An external ATU is needed though if you wish to operate a single antenna on multiple bands where the SWR of the antenna will be higher than the amplifier network's capability to match it.

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You'll want to keep the SWR of the feed line to the antenna below the limits that the amplifier can handle (typically 2:1 or so), so whether you'll need an antenna tuner or not depends on the antenna and the feed line. Some antennas, like a dipole at its design frequency or a store-bought yagi or vertical, have SWRs below those limits, in which case you wouldn't need an antenna tuner. Many multi-band wire antennas require a tuner. In any event, an antenna tuner and an SWR indicator (if the tuner or amplifier doesn't include one) give the operator more versatility.

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  • $\begingroup$ If an answer is satisfactory, please consider accepting the best one by clicking on the check mark, otherwise the site will think that the question hasn't been satisfactorily answered. It never hurts to wait a day or two before selecting an answer, in order to attract more answers ;) $\endgroup$
    – rclocher3
    Commented Dec 7, 2016 at 18:19

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