The Antenna Tuners Page

by Josh Rovero, KK1D

Updated: September 25, 2010

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. MT-3000A Schematic with component values redrawn by Jim, K5LAD.
4. Instruction Manual for Dentron MT-3000A Antenna Tuner, Dentron, 1978

MT-3000A photo from the eHam.net web 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 (42 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 30 year old 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.

The shack tuners include a Dentron MT-3000A and a LDG AT-100ProII.   The Dentron matches the all band dipole on all bands except 10 meters. The LDG matches it on all bands except 160m.   It's hard to beat the convenience of the LDG -- it automatically matches after "training" on regular operating frequencies, or when the SWR exceeds a set threshold.   It makes band changes a snap.