Hi Gang,
The tests on the LDG AT-11 QRP automatic tuner are completed.
Unfortunately, because it is an automatic tuner, I had to modify
the test methods. This means that the summary below will not
compare directly to the previously reported numbers. I've tried
to make a statement in each of the usual test areas.
The AT-11 was very efficient on the bands tested. In addition,
the SWR bandwidth was very wide. In most cases, one tuner
setting would cover 1 mHz or more with less than 1.5 SWR.
The AT-11 was tested on 80M, 40M, 30M, 20M, and 10M. A noteworthy omission
is 160M. (other bands omitted - 17M, 15M and 12M) My
tests gave inconsistant results on 160M so I chose to eliminate
that band from the test report. Many tuners are inefficient on
this band, and had I been able to include 160M data, this tuner
would probably have been less efficient. (opinion, not fact)
It is important to remember that the information below is a summary,
and cannot indicate performance on any individual SWR/Frequency combination.
Some tuners perform better on certain frequencies than
others. These results are based on testing one or two tuners which
may or may not be representative of all of the tuners of the same
model. (particularly true of kits which may have variations in wire routing)
Test Results:
POWER REQUIRED - Normally, I do not make power tests. The AT-11
tuner requires a certain amount of power to make it cycle,
however, so this is of interest to QRPers. The literature
indicates .1 watt minimum.
However, .1 watt would cycle the tuner only if the antenna load
was 50 ohms. Otherwise, up to .7 watt was required to produce an accurate
cycle. In some cases, if the tuner was fed less than
adequate power, it would give a false reading. (indicate a match of less
than 1.5 SWR, when actual SWR was 2.0 or higher)
The tuners are normally tested for five conditions:
RANGE - The number of SWR/Frequency combinations, within the
advertized frequency range of the tuner, that could actually be
tuned to 1.1:1 SWR or better.
Results:
MFJ-949E 137/162 (137 out of 162 possible)
ZM-1 140/144
St. Louis 138/144
Murch 2000A 71/72
LDG AT-11 (see notes 1,2)
Note 1: The AT-11 is designed to tune to 1.5 SWR or less. It
would often tune to 1.0, 1.3 or something else below 1.5. From a
practical standpoint, these SWRs are acceptable. Within it's
advertised range, (excluding 160M) there were just 3 combinations
tested which did not tune to 1.5 or better. (This is similar to
the results obtained with the other tuners tested.)
Note 2: LDG spells out the range their tuner will cover clearly,
ie., from 6 ohms to 800 ohms impedance. This was an accurate representation.
EFFICIENCY - The number of SWR/Frequency combinations, within the
advertized frequency range of the tuner, which resulted in less
than 20% (approx. 1 db) power loss.
Results:
MFJ-949E 49/162
ZM-1 60/144
St. Louis 1/144
Murch 2000A 35/72
LDG AT-11 30/40 (excluding 160M)
AVERAGE LOSS PERCENTAGE - The average signal loss of all of the
SWR/Frequency combinations which would match to 1.1:1 or better.
Results:
MFJ-949E 29%
ZM-1 22%
St. Louis 43%
Murch 2000A 22%
LDG AT-11 14% Note: Match was 1.5:1 or better, not 1.1:1.
SWR BANDWIDTH - The number of SWR/Frequency combinations, within
the advertized frequency range of the tuner, which enabled a
tuning range greater than 5% of the primary frequency. (5% on
7.2MHz is 360Kc) (Once the tuner is set, how far can we tune from
the frequency before SWR climbs to 1.5?)
Results:
MFJ-949E 73/162
ZM-1 61/144
St.Louis 77/144
Murch 2000A 22/72
LDG AT-11 36/40 (excluding 160M)
BALANCE - The number of SWR/Frequency combinations, within the advertized
frequency range of the tuner, indicating a balanced
output with less than 1.5:1 difference between the lines.
Results:
MFJ-949E 52/81
ZM-1 72/72
St. Louis 72/72
Murch 2000A N/A (Murch is an unbalanced only tuner)
LDG AT-11 N/A (unbalanced only tuner)
TUNER DESCRIPTIONS:
MFJ-949E: A C-L-C "T" design. Uses a tapped air inductor. Rated
at 300 watts. Balun provides balanced output. Tunes 160M through
10M. Case about 3-1/2" X 10-1/2" X 7-1/4"
ZM-1: A "Z-match" design. Uses a ferrite core inductor. Rated at
15 watts maximum. Link coupled for balanced output. Tunes 80M
through 10M. Case about 2-1/2" X 5" X 1-1/2".
St. Louis: A C-L-C design. Uses a tapped ferrite core inductor. Rating
unknown, probably 25 watts or more. Balun provides balanced output. Tunes
80M through 10M. Case about 2-3/4" X 6-1/4" X 5".
Murch UT 2000A: An "Ultimate Transmatch" design popular in the
1980's and found in the 80's Handbooks. (This one did not have
the "SPC" mod) Rating 2000 watts. Unbalanced output only. Tunes
80M through 10M. Case about 5-1/2" X 12" X 12".
LDG AT-11: An automatic tuner consisting of the "L" design with switched
capacitance and inductance. Power rating is 10 watts.
Tunes 160M through 10M. Case about 5" X 6-1/4" X 1-1/4".
The test methods used were described by Frank Witt, AI1H, in his
April, May, 1995 articles in QST, and in the Antenna Compendium V.
CUL,
Bob Kellogg, AE4IC, Greensboro, NC
Prolably, but not nececelery. - Benny Hill
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