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MFJ-998 1500 Watt Automatic Tuner Review

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  #17  
Old 10-24-2011, 09:39 AM
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Quote:
Originally Posted by Needle Bender View Post
will it also do balanced 450 ohm line? whats the maximum swrs it is rated to handle?
If you use balanced line, you would use an external balun and attach to one of the coax connections. The tuner does not have an internal balun to allow you to choose one that is suitable for your application.

If you use a long or random wire, you can use the terminal shown in this pic:



It's tuning impedance range is from 12 to 1600 ohms, which equates to a max SWR of 32:1.

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  #18  
Old 10-25-2011, 10:36 PM
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Default MFJ-998 Performance

Putting the MFJ-998 to Work

I've covered all of the major functions of the MFJ-998, so the only thing left is to describe how it has been working for me.

So far, I've tried this tuner on two different antennas, and I intend to try it on several others. My primary test has been on an Alpha Delta DX-CC. This antenna is a fan dipole for 10, 20, 40, and 80 meters, with loading coils to shorten the 80m segment. Generally, the tuner has no trouble tuning the band edges for each band that the antenna is cut for, so the interesting test is how well it tunes the WARC and other bands. I've also experimented with tuning all the bands on my Cushcraft R6000 vertical, which is designed for 6m-20m.

When you first initiate the tuning cycle, the tuner takes anywhere from a few seconds to about 30 seconds to find a match that is equal to, or lower than the target SWR you set in the menu. Once it finds a suitable match, the tuner stores the capacitance and inductance settings into memory, and the next time you key up within several kc's of the stored frequency, the tuner switches instantaneously to the correct setting. Thus, the best thing to do when you install this tuner is to switch to each band to initiate a tuning cycle to allow the tuner to store an initial setting for that frequency. If you use an antenna with narrow bandwidth on a particular band, tune up each of the band edges. After you do this initial procedure, your future tuning cycles will either be instant or only take a few seconds.

This tuner has no trouble tuning my 80, 40, 20, 10 meter dipole fed with coax for 60, 30, 15, and 17 meters. Unfortunately, I could not get the tuner to load up 12 meters upon initial installation. The original tuner that i replaced was an Ameritron ATR-30 manual tuner, which will load up a paper clip. The ATR-30 had no problem with 12 meters, but the MFJ-998 would not.

It's important to understand that no auto tuner is infinitely capable due to the way they are designed. With a good manual tuner with a roller inductor, the operator has almost an infinite range of adjusting inductance, as well as adjustments to capacitance on both the transceiver and antenna side of the antenna circuit. However with an auto tuner, the capacitance is applied to either the transceiver or the antenna side. The MFJ-998 will attempt to apply the capacitance to either side to find the lowest match, but it cannot apply capacitance to both sides at the same time. As a result, auto tuner's tuning ranges are always limited. The MFJ-998 is no different.

When using auto-tuners with odd antenna lengths, you will quickly discover that the feed line length matters. The MFJ-998's manual does a good job of outlining the feed line considerations that can affect the tuning capabilities. To get the tuner to load up 12 meters on the fan dipole, adjusting the coax length was the trick for me.

Interestingly enough, I was able to tune all bands between 80 meters and 10 meters on the Cushcraft R6000. I already knew that the R6000 was resonant around 4Khz, but I really wasn't expecting the tuner to be capable of tuning the entire 80 and 40 meter band, as well as 60m. The tuner is NOT designed for 6 meters. If you attempt to use it there, the frequency counter will not only be unable detect the correct frequency, it will also not be able to load up the antenna as desired.


Transceiver SWR Protection Considerations


Occasionally when trying to load up an antenna that presents a very high SWR to the transceiver, it will be difficult to get the MFJ-998 to start the tuning process while in Auto mode. This behavior is caused by the transceiver detecting a high SWR condition and reducing the power output below the necessary power level to make the MFJ-998 start it's tuning cycle. Fortunately, there is a trick to making this work: While emitting a carrier, press either the L-UP or L-DOWN buttons to manually change the tuner inductance. After only a couple of changes, you will likely find an inductance setting that will cause the antenna's impedance to show a low enough SWR to the transceiver to cause it to output enough power for the MFJ-998 to start it's tuning cycle.

I've compared the SWR readings on the MFJ-998 to both external and internal transceiver meters and will discuss these finding next. The results are interesting...

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  #19  
Old 10-30-2011, 11:40 PM
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How the SWR Bridge Stacks UP

Before I discuss the MFJ-998's SWR bridge reading, it bears mentioning that if you hook up several different SWR meters to your station, you will probably get several different readings. Because of the precision and stability of these devices, you will get similar yet slightly different readings. As a result, it should not be a surprise that the MFJ-998 displays the same behavior as most other meters.

I compared the 998 against an external Daiwa CN-801 meter and the internal meter of the Elecraft K3. I also ran some tests with my Bird 43 inline and compared to the meter on the Ameritron ALS-1300. The results between the various meters was often slightly different, but within a tolerance that doesn't really make any difference. However, there are some exceptions.

Usually the MFJ-998 loads up my various antennas without a problem. However, there are a few frequencies on these antennas where the SWR calculation is off, enough to cause some issues. For example, on 29.7 Mhz, the SWR on my 10m inverted V reads 3.3:1 on my K3 with no tuner inline. When I engage the MFJ-998, it finds a match that it reports as 1.0:1. However, my K3 still sees 2.3:1. The external Daiwa CN-801 reads 1.9:1. The real problem is that the Ameritron ALS-1300 1.5 KW amp also sees 1.9:1, which is too high. This SWR reading causes the amplifier to trip into protection mode.

There are two ways to solve this problem. The first is to run the tuner's calibration procedure, which I've done. Unfortunately, this didn't help much. The second solution is to manually adjust the tuner until you get a satisfactory SWR reading on your external meter. This is accomplished by adjusting the capacitance up or down and also the inductance up or down while the tuner is not in automatic mode. When you find a good match, just overwrite the tuner's memory setting for that frequency and it will use the new setting every time. To overwrite the memory, press TUNE, C-DN, and L-DN simultaneously. In my example, this tweaking procedure causes the tuner to report 1.5:1 SWR, the transceiver to report 1.1:1 SWR, the external meter to report 1:3:SWR, and most importantly, the amplifier to report 1.5:1 SWR, which is is quite happy with.

The bottom line is this: 90% of the time, the tuner matches your antenna without problem. Sometimes however, the internal SWR bridge just doesn't read an accurate enough measurement during the tuning procedure. When this situation occurs, adjust the tuner manually while using an external meter and save the resultant setting. It will only take a few seconds to find the correct adjustment.

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  #20  
Old 11-03-2011, 09:28 AM
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I mentioned in the last update the tuner's calibration procedure. Check out the video I posted in another thread that walks you through the procedure:

MFJ-998 1.5KW Autotuner Calibration procedure video

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  #21  
Old 11-03-2011, 07:09 PM
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Have you had a chance to come pair the power meter with a bird 43p

Thanks

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  #22  
Old 11-04-2011, 11:05 AM
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Quote:
Originally Posted by purenrg View Post
Have you had a chance to come pair the power meter with a bird 43p

Thanks
Yes, if you notice in the video link I posted, that's what I was using for the calibration procedure. The power measurement of the tuner is pretty much right on with the Bird 43P. Remember, the PEP tolerance for the Bird 43P is +- 8%. I don't know what the tolerance on the MFJ-998 is, but any readings that I saw between the two where well within 8%.

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  #23  
Old 11-04-2011, 09:14 PM
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Ny bad
Thanks for the review Moleculo!!!

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  #24  
Old 11-17-2011, 09:22 PM
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It's been a little while since I made any updates on how the testing on this tuner is progressing, so I thought I would make a few comments.

Now that the tuner has a few memories stored for various frequencies on each band, I almost forget it's there. Changing frequencies or bands is almost just a matter of dialing the new frequency up and talking and letting the tuner detect the new frequency and changing to its saved memory setting. If I want to be more careful, the TUNE button takes care of matters.

I have observed that using 12 meters on my antenna system with this tuner continues to be a problem. This situation for me is an example where the manual tuner does the job but the auto tuner struggles. Interesting enough, the tuner built into the Elecraft K3 is able to load up 12m on this antenna.

Another thing to note is that I have run full legal limit into this tuner and it has yet to fail.

Testing continues...
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