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I recently picked up one of these neat antenna couplers. I've read about them and wanted to find one for myself. My main interest is in comparing to MFJ and other cheap but expensive units.
First thing I noticed is like all Dentron antenna couplers, much better quality in components and assembly.
First there is more space between the inductor and cabinet. Second the plate spacing of the capacitors.
The one commonality that I have found with Dentron and MFJ is that the capacitor knobs are indexed backwards. Minimum capacitance is 10 and maximum is 0.
I first noticed this when I purchased my first MFJ coupler. In over 30 years as a broadcast engineer and a technician before that I never saw minimum settings of anything at MAXIMUM and maximum setings at MINIMUM. Except on MFJ and Dentron. Maybe there are others, and I have not found them.
Maybe that is why MFJ and others tell people incorrectly how to set their antenna coupler. Instead of maximum capacitance on 160 & 80, and about 75% of full capacitance on the mid bands, and 1/2 capacitance on 20 and above they just tell everyone to set them 1/2 way and let you be confused when you think your lowering capacitance by approaching 0 and increasing it as you approach 10; in reality you are doing the opposite.
Not only that if I would have designed machine control systems like that there would have not only been many confused operators and confusion on the production floor, hazardous operation would have been created.
As for the rest of the unit, I found what everyone else that posts on these notes, is in the design a second toroid was added for 160 meters. That seems to be the weak link for 300W. I don't like tiny wire. If it ain't made to survive full rated power at A.M. it's junk. I'm as stubborn that way as those who like to call MFJ mighty fine ......
In actuality, if it works it ain't junk. Things that work, work. Just some things are built to better quality standards than others.
For the Manual. There seems to be only one .pdf of this manual on line. No problem with that. I post this one because my Jr. Monitor came with a manual. The manual is a bit wrinkled, but it scanned ok.
What I found interesting is that Dentron changed the initial settings with an added sheet.
What else I found is that some of these units had the toroid and some did not. Some of the units had the ground jumper for the toroid and some did not. It also is not in a before or after certain serial number. Search on line and you can find low serial numbers with the toroid and jumper binding post and higher serial numbers without. I have not yet found any with the correct spelling on the label (MONITER).
So if you remove and reinstall the capacitor knobs the charts are null and void. Anything Dentron states set to 0 just set to 10. 4 will become 6. 5 will stay 5.
As for operation, this thing works like a charm. I was able to match 80 through 10 on an end fed wire and on a dipole. I could match 160 through 10 on my vertical.
Worst case SWR was 15:1 and 12.3:1 on the wire antennas measured with a RigExpert AA-55 Zoom. Same antenna measurements after the Jr. Monitor match were all less than 2:1.
Vertical antenna worst SWR was 18:1 on 160m which matched 2.2:1 and 2.6:1 after the Jr. Monitor.
Loss? I did not measure antenna current or field strength, but I did make CW contacts Friday and Saturday night to CA and OR as well as the U.K, Germany, and Italy all QRP.
I used 25W on SSB throughout the USA the same 2 nights.
Since MFJ has ceased production we may not get many new (only what is left in stock) MFJ anything, but for years there will be used on the market.
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