May 22, 2012

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Antenna Tuners (ATU)

Impedance matching in a world of mis-matches


Looking for that perfect match?  Well, stop spending time on those singles dating web sites and take a look at the plethora information published in the amateur radio press on this timeless topic.  But who really knows how these ATUs operate?  Which design is efficient and which is bogus?  Why not just toss in a balun?  How much power capacity is required?  Where should you optimally place the ATU?   

For answers to these questions and much more, join in on this CWTD session and perhaps pick up a few gems of an idea that you can try out with your own antenna “system”.

73, George N2APB  & Joe N2CX

Audio Recording ... (Listen to the MP3 podcast)

Discussion Notes:

<20:02:15> "Joe N2CX":
<20:02:42> "Kelly K4UPG": Tnx Joe for Link. This is my fav subject
<20:22:54> "W2AEW - Alan": That kind of coil-to-case spacing is NOT common in store bought tuners due to cost.
<20:25:01> "Kelly K4UPG": Somewhere along the line can you explain the pros/cons of using plastic enclosures vs metal?s
<20:28:35> "Sam NV1P": i love mine. can it be used on the WARC if a roller inductor or more taps were added?
<20:34:47> "Pete - WB2QLL": You can also use two antenna tuners in "series" if you get desperate. Loss will increase but it may not be significant; the range will increase greatly.
<20:37:32> "W2AEW - Alan": I have a TenTec 238C which is an L-type tuner - very nice.
<20:37:50> "Kelly K4UPG":  nice L type with options
<20:38:54> "WA0ITP Terry": Does the L have only one combination of values for a given antenna?
<20:39:27> "W2AEW - Alan": Terry - yes.
<20:40:42> "W2AEW - Alan": ...or reverse input and output
<20:42:00> "Joe N2CX": QRPp Vol 4 had the St Louis tuner
<20:42:07> "Mike WA8BXN": If L is simpler and better, why are many manual tuners T configuration?
<20:42:17> "Sam NV1P": what are the best values to use when building a "L"?
<20:42:48> "Larry - W2HHV": The Pic-A-Tune ATU at  is a remotely tuned L Network with switchable C. Good matching range data in design documentation.
<20:43:48> "WA0ITP Terry": Here's an interesting T Match Simulator
<20:44:25> "W2AEW - Alan": My favorite ARRL book on this topic is "REFLECTIONS: Transmission Lines and Antennas" by M. Walter Maxwell, W2DU. Very thorough coverage of matching topics
<20:44:44> "Joe N2CX": Indeed the Pic-A-Tune is good example of the auto antenna tuner and good for the homebrewer as well
<20:45:47> "Mike WA8BXN": another issue, T tuner is high pass, L tuner low pass
<20:47:19> "Ray K2ULR": George: That MFJ Loop tuner has an RF ammeter.
<20:48:15> "W2AEW - Alan": I have a ZM-2 also - I really like it!
<20:49:21> "Kelly K4UPG": QST Sept 09 p 35 A Simple Transformer to Measure Your Antenna Current
<20:51:25> "W2AEW - Alan": The ZM-2 has a nifty little LED-based matching indicator
<20:52:07> "Pete - WB2QLL": Need a source of tiny cheap meters, easier to see outdoors than LEDs.
<20:52:34> "Joe N2CX": Pete, Me too!
<20:53:33> "Kelly K4UPG": 200ua S meter type available on Auction site
<20:54:09> "Joe N2CX": N7VE SWR meter uses toroid xfmr to get higher voltage to light LED
<20:54:58> "Kelly K4UPG": I find hand capacitance issues with plastic enclosures. How to beat that?
<20:55:16> "W2AEW - Alan": example build of ZM-2
<20:55:53> "Joe N2CX": Kelly you can use a metal plate behind front panel to reduce hand capacitance
<20:57:00> "Kelly K4UPG": tnx Joe will try that
<21:00:02> "W2AEW - Alan":
<21:04:39> "WA0ITP Terry": Neat to build one for forward voltage also.
<21:07:21> "Pete - WB2QLL": So what's inside the PAR EndFedz matchbox?
<21:08:02> "W2AEW - Alan": Pete - it's an L-network from what I've seen
<21:16:34> "Kelly K4UPG": Great overview tnx 4 ur effort to put this together!
<21:16:50> "Joe N2CX": AA5TB Steve Yates
<21:16:59> "WA0ITP Terry": Thanx vy much, great stuff and nicely done.
<21:17:30> "Kelly K4UPG": Love the references!
<21:17:48> "Ron KK4DWE": Very nice info guys!! Will be back next Tuesday.
<21:20:21> "W2AEW - Alan": 73 from NH hotel room
<21:20:23> "Armand WA1UQO": Thanks George and Joe, good info and great references! Looking forward to next week.
<21:20:37> "Joe N2CX": Can you tell I love antennas?


Antenna Tuners (ATUs)

The Basics

[From Wikipedia] … An antenna tuner, transmatch or antenna tuning unit (ATU) is a device connected between a radio transmitter or receiver and its antenna to improve the efficiency of the power transfer between them by matching the impedance of the equipment to the antenna. An antenna tuner matches a transceiver with a fixed impedance (typically 50 ohms for modern transceivers) to a load (feed line and antenna) impedance which is unknown, complex or otherwise does not match. An ATU allows the use of one antenna for a broad range of frequencies. An antenna plus matcher is never as efficient as a naturally resonant antenna due to additional induced losses on the feed line due to the SWR (multiple reflections), and losses in the ATU itself, although issues of pattern and capture area may outweigh this in practice. An ATU is actually an antenna matching unit, as it is unable to change the resonant frequency of the aerial. Note that similar matching networks are used in other types of equipment, such as linear amplifiers to transform impedances. See impedance bridging for details.


Discussion Outline  


         Actually, "Antenna Matching Units" ...

         Why do we need them?

     Modern rigs  designed for 50 ohms

     Many antennas/feedlines are not

     Non-resonant wires

     Open-wire feedline

     Multiband operation


Fig 15.25 end-fed wire impedance plot


         When am I matched?

     Match transmitter or receiver impedances

     Usually SWR close to 1:1

     Often anything less than 2:1 is ok


         Want tuner to have “good” traits

     Easy to tune

     Simple construction



     Choose ant two...


         ATU configurations

     Original “boat anchors” didn't need them

     Built matching circuits into final tuning

     Solid state rigs designed for “no-tune” operation

     Designed to drive 50 ohm coax



         Types of common ATUs

     Johnson Matchbox

     Link-coupled balanced tuned circuit

     True balanced or unbalanced operation

     Ham standard for years


Pix and schematic of Johnson Matchbox



         Utimate Transmatch

     Simple operation

     Tried to be simple multiband wide range tuner

     Very popular

     Not inherently balanced




Fig 15.31 Variations of the Ultimate Transmatch



         Tee Tuner

     Two variable capacitors and one inductor

     Wide tuning range

     Simple construction

     Popular tuners from many manufacturers use this configuration

     Inherently unbalanced


St Louis Tuner ... a T-type tuner




     Very simple construction

     Very wide tuning range

     Can be cumbersome to tune

     Inherently unbalanced


QRP Kits SLT+ Tuner schematic






Z-Match Tuner

     Fairly simple construction

     Easy to tune

     Tunes wide impedance range

     Balanced or unbalanced




         Other tuner configurations

     How big is the sky?

     Homebrewers delight tuner for end-fed wires

     Requires hands-on tuning

     Wide range matching capability

     Also used for 43 foot “all-band” vertical


Fig 15.25 schematic


         SWR measuring important to tune ATU

     Ideally want 1:1 SWR

     Anything under 2:1 usually no problem

     Often built into tuner


Schematic of Optical SWR Meter




Other SWR meter pix/schematic?


         Losses in tuners

     Try to keep less than 10% (about dB)

     Losses increase the farther antenna Z is from 50 ohms

     Baluns ok in resonant system

     Losses increase far from design Z

     Losses can be high if mis-applied

     Antenna broadbanded by balun is inefficient


         How to evaluate tuner?

     AI1H methods in QST references

     Also results of ARRL review of four high-power tuners

     Can also do comparison tests of antenna with various tuners


         My antenna don't need no stinking tuner.

     Cecil W6RCA all-band dipole

     Switched in appropriate lengths of open sire feedline to “tune” antenna


W6RCA no-tune antenna.jpg









From: Joe Ostrowski, KI5FJ

Folks I offer the following to the FB presentation:

  • Always consider RF Safety when constructing indoor ATUs.

  • My thoughts and simple design of a Remote ATU, QST October 2011, mention placing the ATU in a metal enclosure if used indoors.

  • If your SHACK includes a PC, the RF emitted from an unshielded ATU, even at QRP levels, can cause issues.

  • In my opinion, most antennas will not present a SWR less than 2:1  in BOTH the digital and phone portions of several bands.

  • There is no free lunch, impedance matching is a necessary evil.

  • If you are going to purchase an ATU, first consult others as to their experiences.

  • Advertising will never tell all the facts.

  • I believe a 300 watt rating will probably not self destruct at 100 watts SSB.

  • A 3000 watt rating really means OK at less than 1000 watts RTTY.

  • Internal rig ATUs can not outperform a well designed external ATU.

Thanks to the crew for the informative presentation !



General ATU Literature

1)     A 100-Watt Compact Z-Match Antenna Tuner, by Phil Salas AD5X,

2)     BLTplus , by QRP Kits,

3)     M0EZP Z-match ATU covering 160m-10m, by

4)     Review of different ATU designs, by David Knight G3YNH and Nigel Williams G3GFC,

5)     The Ultimate Transmatch, Lew McCoy W1ICP, QST for June 1970,

6)    St Louis Tuner Norcal QRPp Volume 4


7)     Elecraft T-1 Automatic Antenna Tuner, <>

8)     Johnson Matchbox (no longer in production), <>


9)     Z-Match Tuner Design, <>

10) Radio Communication Handbook, 11th Edition, RSGB, Chapter 15


11) W6RCA's No-Tuner, All-HF-Band, Horizontal, Center-Fed Antenna



11) QRP Kits SLT Plus Tuner.


 ATU Loss References

1.      ATUs, Deltas and Losses,  1996 W4RNL, QQ Jan 1996, P.18

2.      A Balun May Be Eating Your Lunch,  KN1H, QQ April 1987, P. 10

3.      “How to Evaluate Your Antenna Tuner,” F. Witt, AI1H, QST , Apr 1995, pp 30-34 (Part 1 ) and May 1995, pp 33-37 (Part 2 )

4.      Evaluation of Antenna Tuners and Baluns–An Update, Frank Witt, AI1H, QEX Sept/Oct 2003, p. 3

5.      “QST Compares : Four High-Power Antenna Tuners,” QST , Mar 1997, pp 73-77

6.      “Baluns in the Real (and Complex) World,” F. Witt, AI1H, The ARRL Antenna Compendium, Vol 5, (Newington: ARRL 1996), pp 171-181




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