Bit About Antenna Tuners

Something has bugged me for a long time — the way some radio manufacturers market and sell their transceivers with built-in automatic antenna tuners. These are almost always intended to be used with antennas that are sold by the manufacturer (for instance, a specific mobile antenna) but this is seldom clear in large print in the adverts.

An unsuspecting ham may think the auto-tuner in his shiny new HF rig is going to work with the new dipole he hung up between the trees, only to discover it’s a hot mess.

Due to their size, most internal tuners (there are some exceptions) can manage only a slight mismatch in impedance and cannot begin to cover a wide range like that presented by ladder line and wire antennas. The explanation for this is fairly straight forward.The antenna and feed line present a load to the output of your transceiver. Most modern equipment has been designed to work with a load impedance of 50 ohms. Get close enough to that, and the transmitter is a happy camper. But if the load impedance is something other than 50 ohms, you have a mismatch. A mismatch causes a certain amount of the power that you’re trying to get out to be reflected back down the line — where it encounters forward power from the transmitter resulting in standing waves on the feed line.

You’ve doubtless heard of this in discussions about SWR or standing wave ratio.

A high SWR can cause considerable RF voltages in the feed line — and at the output of your shiny new radio. This isn’t healthy for modern transceivers (tubes are a little more forgiving) so manufacturers have taken to protecting equipment from this condition. When it’s sensed, your rig may fold back its output power, or shutdown altogether in order to prevent damage.

And this is why hams use antenna tuners. Most of us would like to be able to operate over many frequencies with a single antenna. Since the impedance of that single antenna will change depending on the frequency of the transmission, a tuner becomes a useful tool.

Basically, a tuner is a combination of inductors and capacitors that act to balance the load reactance at the transceiver end of the feed line. With the reactance effectively canceled, the load impedance at the transceiver is 50 ohms and all is right with the world.

Well, maybe not everything. Your antenna might still be a highly inefficient radiator — but with a 50 ohm load, the transceiver will happily pump all of its juice up into that inefficient aerial system as though it were perfect.

What’s really taking place here is that the load mismatch has been moved down the feedline from the output of the transceiver to the output of the antenna tuner. The reflected energy and standing waves still exist, though a well-designed tuner should be able to handle it better than your transceiver. The tuner protects the transceiver and permits it to generate full-power output.

Higher power and wider ranging tuners are physically larger than can be made to fit inside most tiny, whiz-bang transceivers. Physics is a tough master that demands attention at some point.

The moral of the story is that wire antennas, ladder line and open feed lines are great systems for launching RF into the aether, so long as you have a proper antenna tuner in the circuit. But internal tuners offered with most modern transceivers simply won’t cut it with these kinds of antenna systems.

There are notable exceptions. The low-power internal tuners offered by Elecraft and the slightly larger internal tuners offered by TenTec are downright amazing. There may be others that I’m not aware of so do your homework but as always, the buyer should beware…


Filed under: Ham Radio Tagged: antennas
Jeff Davis, KE9V, is a regular contributor to AmateurRadio.com and writes from Indiana, USA.

12 Responses to “Bit About Antenna Tuners”

  • Matt W1MST:

    Great post, Jeff. Internal tuners can be useful but they are certainly not going to solve every problem.

  • Charlie G4EST:

    Jeff
    I cannot say that I have experiences these issues, albeit that I have only had 2 rigs with a built in ATU, the former being the kenwood TS570D and the current the Kenwood TS990S.
    I use a 65′ end fed through a 9:1 balun which is a resonable match 20m through to 10m but is way off on 80m with 40m being reasonable. A Snowdonia Radio company HF360 vertical was poor from 20m to 80m (also with a 9:1 balun). These readings were taken using an antenna analyser and the latter being so bad I switched to a Gap Titan DX which is absolutely brilliant.
    To get back on point the auto ATUs in both rigs coped from 10m through to 80m.
    maybe kenwood ATUs are more adjustable, but I have no antenna issues with these rigs.

  • “These are almost always intended to be used with antennas that are sold by the manufacturer (for instance, a specific mobile antenna) but this is seldom clear in large print in the adverts.”

    Jeff, I guess I’m not clear what you mean here. I can’t recall seeing any manufacturers who attempt to hide the capabilities of their built-in antenna matching devices, nor have I seen any that were primarily intended for antennas manufactured by the same guys. Most clearly state the limitations of their devices, though that can be tricky.

    These “tuners” respond to specific impedances, not necessarily to standing waves or even reflected power. Those impedances can be quite complicated. A 5:1 SWR might be no sweat but a 3:1 faced by the very same “tuner” could be impossible to find a match.

    Built-in automatic matching devices came into vogue when finals mostly became solid-state devices, more susceptible to damage if facing a complex impedance. Not only were tube-type transmitters more “forgiving” of mismatches as you note, but they typically had a tuned output–made up of coils and capacitors–with which we “tuned” the output of the rig to more closely match the impedance at the antenna connector.

    If you get bored sometime, you may want to see my article titled “Resonance Schmesonance!” at http://www.eham.net/articles/25521

    73,

    Don N4KC
    http://www.n4kc.com
    http://www.donkeith.com

  • yle N4NSS:

    One thing to note is that tuners really don’t tune the antenna. You can’t make a non-resonant antenna resonate with a tuner which is more correctly defined as a matching unit. A resonate antenna always performs better than the non-resonate antenna. What a “tuner” really does is create 50 Ohm load for the transmitter. RF gets to the antenna and still gets the hopeful result, RF to the airwaves. Correct me if I’m wrong. P.S. I love my Elecraft tuners!

  • Agreed on all except: “A resonate antenna always performs better than the non-resonate antenna.”

    Not true. See the aforementioned article…in the comment just before yours.

    73,

    Don N4KC
    http://www.n4kc.com
    http://www.donkeith.com

  • Joe KB3PHL:

    I assume this write up about internal tuners is intended for new Hams because for the majority of us this is Ham Radio 101 stuff. But generally speaking most if not all mobile radio’s & the majority of the larger base type rigs that come with internal tuners are 3:1 ratio tuners with the exception being the previously mentioned Elecraft, Ten-Tec & possibly some Kenwood’s having 10:1 ratio internal tuners. My Ten-Tec Jupiter has a 10:1 ratio tuner made by LDG. It would be nice if they all came with 10:1 ratio tuners & it would really be great if they came with fully automatic memory tuners.

  • Bob W8RMV:

    I trust your experience is true. But my experience with the TS-590S is much different. Although it is spec’d at a 3:1 tuner, it actually can match much closer to 10:1 for some frequencies/antenna system. And do it very quickly. It is the best internal autotuner I have experienced. It kills the AT in my FTdx3000. 73 Bob

  • Joe KB3PHL:

    Bob W8RMV, that’s very interesting about the Kenwood 590S. I’d like to get a 590S someday, so I’ll have to remember that about it’s tuner.

    73’s Joe KB3PHL

  • Eric Carlson AJ4LN:

    I have a Kenwood TS-570D(G) and a TS-590S, and they both have excellent internal tuners. I’ve even been able to use my G5RV on 160M with these 2 radios and their internal tuners, and they’ve worked fine on the rest of the HF bands.

    Though recently the rope holding up one leg of my G5RV broke, so half of the antenna is dangling in a tree, so the SWR is way off on the upper half of 80M now, and the TS-590S can’t tune that part of the band at the moment, though I was still able to make contacts in that part of the band for the NAQP SSB contest, even though the radio rolled back power to protect the finals. I’ll have to rehang my G5RV once the trees are bare again in late Fall.

  • David Lowry WX5DL:

    I’m currently using an Icom 746pro with a W5GI co-linear dipole (mystery aantenna). My rig expert analyzer shows 10-1 swr on some frequencies but the “tuner” in the Icom handles the mismatch just fine. I think auto tuners have really improved since they were first introduced and most will perform well up to 10-1. Some of the early ones that would only match a 3-1 were all but useless. Most radios will work fine at 2-1 with no tuner!

    I also have a couple of LDG tuners that work well and a Elecraft T-1 that is truly amazing for QRP.

    At my home qth and especially for portable operation, one antenna needs to work on multiple bands. A tuner makes that possible and a lot more fun.

  • David WB4ONA:

    I have an old TS-450SAT. I can attest to the fact that the internal antenna tuner is quite good. It makes me wonder, If Kenwood could do it long ago with the TS-450SAT, why couldn’t Yaesu put a similarly capable HF tuner in the modern FT-450D transceiver?

  • Marc W4FDU:

    I agree 100% with Bob W8RMV. The AT in my TS-590s is amazing. It tunes my 160M InvL just fine anywhere on 60M and anywhere on 160M. It is MUCH superior to the AT in the old TS-570sg. Also tunes the 40M dipole perfectly on 6M: I have worked CA on 6M from EM65 numerous times. 73

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