Recently due to the addition of an SG-500 amplifier to our IC-756 Pro transceiver with auto-tune we were forced to look into antenna tuners. Being able to borrow an older model of the MFJ-986 from my nephew Tom, (K9XV) I was able to secure successful operation on 10 thru 80 meters with the new amplifier and tuner combination with our G5RV 104 Ft. antenna with RG8-X coax feed to the tuner. We ordered the NEW model in Jan of 2004 and proceeded as follows:
Upon reviewing the manual with the NEW MFJ-986 we were at first unable to obtain any dip or proper tuning. Further reading still left us with no results. Taking the covers off both the “Old” and “New” model and comparing capacitor and inductor settings lead to some proper results.
On page #4 of the manual it never states where to set the capacitor value as a starting point.
The correct setting is “O” (Start). However, on the older model it was on #5 approx. mid-point of capacitor. Also on the older model the “lower numbers” on the Inductor were a starting point and our previous final settings were only up to # 039 for 80 meters. Higher bands were lower numbers.
On the NEW model the “higher numbers” on the inductor are the minimum inductance and fully clockwise. The #120 is approx for 80 meters and #163 worked on 10 Meters.
Also a note, on Page #4 says max power is with capacitor and inductor set at the lowest front panel numbers, which is a little misleading.
Using a “0” cap setting and starting at the highest numbers, a setting was found for 17 meters our starting band for trial settings. A setting of –2 on the Capacitor and #160 on the Inductor proved to work properly.
Note the negative setting about ¼” – 3/8” below the “O” mark and no marks to use as a reference.
Placing a white tape label allowed us to make our own scale below the Zero location.
Further testing found settings for 10 meters thru 160 meters and was logged for reference.
Also settings for our dummy load were also noted, however these always required a major change for the capacitor setting and about the same for the inductance. See chart below.
With the covers off both units, the NEW one seems to have a better coil with a much larger roller contact connection and the same capacitor. Likewise the other items inside look very similar and the rear panel is about identical for connections. The new higher 300- watt vs. 200 watt reading on the low range watt meter/SWR setting is an improvement. The reflected range is to 60 Watts vs. 50 Watts of the old unit.
Some of the reasons we purchased the MFJ-986 was for the dual cross-needle watt/SWR meter, and the quick tuning feature of just two knobs the (one) capacitor and inductor of the differential “T” unit. We have been very pleased with the tuner and find it can give a perfect match to my G5RV antenna with no reflected power showing when dipped properly. I always tune with the Transceiver power only at 25 watts and have found on all bands that this same setting is also exact when the amplifier is turned on so no tuning with the amplifier power is necessary and this should add life to the contacts on the rotary tuning coil.
The manual has some good ideas and incase of difficulties help areas and a good discussion on PEP power and some of the newer standards on power ratings. Some minor updating of the manual on 1st owners start up and using similar terms with reference to the dials on the tuner, rather than referring to min or maximum inductance may be helpful for a quicker tune up the first try.
I have made up a chart for the NEW and older units, which may be of general use, if others have a similar G5RV antenna.
Using a tuner gives me an extra tuned circuit going to the antenna with my broad band SG-500 solid state amplifier and no TVI, phone, computer or radio interference is noticed in our home with full 500 watt output. Try a tuner with your antenna it probably will provide an improvement for your station.
Last year an article in Feb 2003 issue of QST tested several tuners including the MFJ 986 and can serve as additional reference for comparison.
NEW MODEL 986 DIAL SETTINGS “OLD 986 DIALS”
|
BAND |
FREQUENCY |
CAPACITOR |
INDUCTOR |
CAPACITOR |
INDUCTOR |
|
10 METERS |
28475 KC |
“0” |
163 |
3.75 |
004 |
|
15 METERS |
21350 KC
|
“0” |
163 |
3.5 |
004 |
|
17 METERS |
18130 KC |
-3 |
160 |
3.0 |
004 |
|
20 METERS |
14225 KC |
1 ¾ |
156 |
4.0 |
009 1/2 |
|
40 METERS |
7200 KC |
2 ¾ |
148 |
6.5 |
017 ½ |
|
80 METERS |
3900 KC |
2 ½ |
126 |
6.2 |
036 1/2 |
|
160 METERS |
1805 KC 1900 KC |
3 3 |
25.5 38 |
Not Tested |
Not Tested |
DUMMY
LOAD ( HEATHKIT CANTENNA)
|
10 METERS |
28475 |
-1.0 |
163.5 |
3.75 |
004 |
|
15 METERS |
21350 |
0.0 |
161.5 |
3.5 |
004 |
|
17 METERS |
18130 |
+ .50 |
160 |
3.5 |
005 |
|
20 METERS |
14225 |
1.75 |
156 |
3.75 |
008 |
|
40 METERS |
7154 |
.25 |
148 |
4.00 |
017 |
|
80 METERS |
3900 |
.75 |
125 |
5.00 |
036 |
|
160 METERS |
1900 |
1.00 |
40 |
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Bob Osterhous W9PSE Indianapolis, Indiana Feb 12, 2004