Impedance matching in a world of mis-matches

Overview

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

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

◦     Inexpensive

◦     Efficient

◦     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

◦     Simple operation

◦     Tried to be simple multiband wide range tuner

◦     Very popular

◦     Not inherently balanced

Fig 15.31 Variations of the Ultimate Transmatch

◦     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 ½ 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

REFERENCES

General ATU Literature

1)     A 100-Watt Compact Z-Match Antenna Tuner, by Phil Salas AD5X, http://www.ad5x.com/images/Articles/Ztuner%20RevA.pdf

2)     BLTplus , by QRP Kits, http://www.qrpkits.com/blt_plus.html

3)     M0EZP Z-match ATU covering 160m-10m, by http://m0ezp.squirrelhouse.biz/Z-Match.html

4)     Review of different ATU designs, by David Knight G3YNH and Nigel Williams G3GFC, http://www.g3ynh.info/zdocs/z_matcing/part_2.html

5)     The Ultimate Transmatch, Lew McCoy W1ICP, QST for June 1970, http://www.arrl.org/files/file/Technology/tis/info/pdf/7007024.pdf

6)    St Louis Tuner Norcal QRPp Volume 4

 

7)     Elecraft T-1 Automatic Antenna Tuner, <http://www.elecraft.com/manual/T1%20owners%20man%20rev%20A2.pdf>

8)     Johnson Matchbox (no longer in production), <http://bama.edebris.com/manuals/johnson/matchbox>

 

9)     Z-Match Tuner Design, <http://www.njqrp.org/mbrproj/zmatch_original.html>

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

 

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

<http://web.archive.org/web/20000612051104/http://people.delphi.com/CecilMoore/mystery.htm>

 

11) QRP Kits SLT Plus Tuner.  http://www.qrpkits.com/sltplus.html

 

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

6.