The Antenna Tuners Page

by Josh Rovero, KK1D

Updated: May 17, 2009

References:

1. ARRL Technical Information Service Transmatch/Antenna Tuner Page.   Some content is for ARRL members only, other articles are available to all viewers.
2. eHam.net Dentron MT-3000A Review
3. Instruction Manual for Dentron MT-3000A Antenna Tuner, Dentron, 1978
4. Instruction Manual for LDG Electronics Z-100Plus Antenna Tuner, LDG Electronics, 2008

MT-3000A photo from the eHam.net web site.        

Z-100Plus photo from LDG Electronics site.

Antenna tuners, transmatches, and antenna matching networks are popular station accessories. There are many types, and they can be misused and abused.

A number of "old school" tuners have limited impedance matching capability, and in some cases, severe losses at certain frequencies and impedances.   Frank Witt, AI1H, wrote a two-part series on the subject, published in QST April/May 1995. A number of network analysis programs (HAMCALC F-16, ARRL TL/TLA/TLW) can be used to model these losses.

At my QTH, the main antenna is a 140 foot (43 meter) dipole fed with ladder line via a remote 4:1 balun and ferrite core RF choke.   It is used on all bands 160m through 10m.   For many years the principal tuner has been a Dentron MT-3000A.   Like many manual tuners, it can match an antenna at a number of different L & C settings, some more efficient than others.   As K5YZS noted in the eHam reviews, even though the components are heavy duty, the relatively small value variable capacitors in the T-network cause about 1 dB loss (20%) on 160 meters.   It does, however, normally allow matching all the way down to 1:1 or very close to it.

Recently, a LDG Electronics Z-100Plus was added to the shack.   It's a whole lot faster to tune (0.1 to 6 seconds) than the MT-3000A, but not perfect.   It is satisfied to match the system to 1.5:1, and sometimes (with indication) between 1.5 to 2:1.   QST subjected the original Z-100 to the Witt treatment, and revealed that it would not match low impedance loads on 160 meters and could be lossy at SWR extremes (>8:1) even when it does match.

The Z-100Plus can't quite match my antenna and feedline on either the lower part of 160 meters or the 17 meter band, so I rely on the Dentron there.   On the other bands, the Z-100Plus provides an acceptable match and tunes very quickly.