A Tiny Tuner For The Low Power Ham

Something that all radio amateurs encounter sooner or later is the subject of impedance matching. If you’d like to make sure all that power is transferred from your transmitter into the antenna and not reflected back into your power amplifier, there’s a need for the impedance of the one to match that of the other. Most antennas aren’t quite the desired 50 ohms impedance, so part of the standard equipment becomes an antenna tuner — an impedance matching network. For high-power hams these are big boxes full of chunky variable capacitors and big air cored inductors, but that doesn’t exclude the low-power ham from the impedance matching party. [Barbaros Aşuroğlu WB2CBA] has designed the perfect device for them: the credit card ATU.

The circuit of an antenna tuner is simple enough, two capacitors and an inductor in a so-called Pi-network because of its superficial resemblance to the Greek letter Pi. The idea is to vary the capacitances and inductance to find the best match, and on this tiny model it’s done through a set of miniature rotary switches. There are a set of slide switches to vary the configuration or switch in a load, and there’s even a simple matching indicator circuit.

We like this project, in that it elegantly provides an extremely useful piece of equipment, all integrated into a tiny footprint. It’s certainly not the first ATU we’ve brought you.

Thanks [ftg] for the tip!

10 thoughts on “A Tiny Tuner For The Low Power Ham

    1. It seems to be designed for the 10m to 40m band, thats a maximum frequency of 30MHz which many might consider close enough to DC that you don’t need to worry too much; f>1 GHz would be a completely different topic. Also even if it adds some stray capacitance and inductance, the thing is a tuner so you can simply tune away some of the mismatch :)

      When building antennas I aim for a SWR of under 1.5, but even with a SWR of 2 I still just grind my teeth and accept it. It’s not a very exact science, you see. Heck, even at SWR=5 you ‘only’ lose half your energy and might be able to communicate just fine as long as your transmitter doesn’t get fried lol

  1. The best tuner that is small I ever had was two counterpoint coils that could slide in and out of each other.

    I used two plastic test tubes, one slightly smaller than the other, and some litz wire I had hanging around.

    You don’t want too many turns as there is losses in every meter of coil wire. But not enough and you might not get a tune.

    It works best with an antenna that needs more inductance to tune, eg wire less than (half?) Quartet wavelength.

    Tuning is quite sharp and on the receive mode, the extra signal strength is markedly boosted when tuned correctly.

    You can also put some fixed or variable caps with it if needed, but my situation this was not the case and it worked for me from 40m thru to 10m.

  2. I have been using a later iteration (beta) of this tiny tuner quite successfully on 15, 12 and 10m. See my QRZ page (va3ip) – I use it at 300mW but it will handle up to 3W and maybe even 5 but NOT designed for long keydown tuning sessions due to tiny components!

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