MFJ 929 Auto tuner

Discussion in 'Amateur Radio Equipment Reviews' started by KU3X, Oct 21, 2009.

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  1. KU3X

    KU3X Ham Member QRZ Page

    I just picked up the MFJ 929 Auto Tuner. I found it to be a great little LC network tuner. There is nothing like a good Tee or Pi network for a broad band tuner but this little MFJ 929 works great.
    I have an LDG Z11 PRO and it can not do half of what the 929 does. I use a shortened dipole for 75 and 160 meters. The LDG won't match the entire band. I have the LDG set to stop at 1.5:1 SWR because above that the solid state rig will fold back its power. On the same two bands, the MFJ 929 will match the entire band. That is, from 3.500 to 4.000 mhz and 1.800 to 2.000 mhz. I changed the default setting for the 929 to not go any higher than 1.5:1 SWR down to 1.2:1 SWR. Not the rig won't stop until it finds a match of 1.2:1 or less SWR. This thing will bring the SWR down to 1.0 to 1 SWR on both bands and the entire band. I then tried to match that antenna to 30 meters, no problem. I tired other HF bands and no problem. I did put the tuner back to the default SWR cutoff range for these tests. I only did the low setting just to test the tuner to see how it would do.
    Current drain is low, just in case you are planning on taking the tuner portable. Less than 800 ma when tuning. It does draw a small amout of current when it use but very little current.
    Unlike the LDG tuner I have, if the tuner sees a perfect 50 ohm @0 J load(perfect match on the antenna), it goes into bypass mode. The LDG I have tried to add inductance and capacitance and the SWR actually goes up. The MFJ knows it does not need anything and you can see on the display the capacitance is zero as well as the inductance. That was the one thing I really hated about the LDG, let alone its limited tuning range.
    I'm sold on this unti, I think it does a fabulos job.
    Barry, KU3X
  2. K4AX

    K4AX XML Subscriber QRZ Page

    I have a couple of the MFJ auto tuners, 993b and 994. Also have the LDG Z11pro, and your experiance mirrors mine.
    The LDG does have two redeeming quality's. One is that if you ever do have to adjust to a lower SWR manually, you can commit that to memory, so when you go back to that frequency the tuner will adjust automatically to what you set it for.

    Second is that it takes batteries, and works well as a remote tuner. I've used it to tune a whip in the car, and had it hooked up remotely to a vertical wire.

    However, the MFJ 993b especially, (similar to yours but with a balun) always knocks the swr to about nothing flat every time, and the digital readout is excellent. It's nice knowing what's going on, and if you change bands a lot, it's cool to look over at the tuner and see the last frequency you transmitted on, so you know if you need to tune up again.
    Last edited: Oct 21, 2009
  3. KU3X

    KU3X Ham Member QRZ Page

  4. KB2ZYA

    KB2ZYA Ham Member QRZ Page

    I have had a 993b auto tuner in my car with a 108 in ols cb wip.I have it gounded real good and use the long wire part to the wip and get 6m-40m. works real good on 20m Dx.I love it
  5. AC0FP

    AC0FP Ham Member QRZ Page

    I'm about to get into the market for a new tuner for my home dipole as my SGC239 has a bad habit of retuning itself to a worse VSWR when you are talking on SSB.

    Does this MFJ auto tuner have any bad habits like the SGC does?


  6. KU3X

    KU3X Ham Member QRZ Page

    I have not found any bad habbits so far. It does everything I tell it to do. It will have its limitations, it is still a simple LC network. It's not as good as my Ultimate Antenna Tuner that I built over 30 years ago but for an LC network, it is one of the best ones I tested so far.
    Don't expect to hang a 4 foot wire out of the back of the tuner and tune every band on HF or erect a 10 meter dipole and expect to get on 160 meters with the system. Common sense comes into play here.
    I send a carrier from the radio and if the system is out of the preset SWR range, a variable you can adjust in the tuner, the tuner will go to work.
    It's as simple as that.

    I saw where the SDG people have an auto tuner with, what I think (?), is a Tee network. I figured that would do a better job but from the reviews I read, which were not good, I was afraid to try one. I did not read any reviews for the 929. I went by the specs and, for me, I made a good choice.
    Last edited: Oct 30, 2009
  7. GM8UPI

    GM8UPI Ham Member QRZ Page

    I have SGC239, but use the remote "SGC Smartlock" unit. Once initially tuned, you can switch to "tune lock". Cures the problem you are finding.
    Although not cheap, you could quite easily buid one yourself. Circuit is given in SGC239 manual.

  8. AC0FP

    AC0FP Ham Member QRZ Page

    I've seen that option but you can do the same thing by switching from "auto to "Manual" with their supplied switch already on the PCB! This doesn't really solve the problem except for a brief period of time! The next time you release it to move to another band and then come back the best match it can find, on the original band, is 4:1.
  9. GM8UPI

    GM8UPI Ham Member QRZ Page

    Hi Franklin (AC0FP)
    Understand what you say about using switch on board. Not sure if that does identical function as "Tunelock" but no matter.
    A problem I had with the SGC239, was the memories becoming full. This was due I believe to the fact that I use unit going portable several times each year, using all sorts of temporary antennas and types. Although the unit would usually get a good match on any initial frequency, it would often try and fail to match after a few overs.
    The problem was completely cured by going through the "clear all memories" sequence (pressing a number of switches at power on), as detailed in the manual, and performance came back 100%.
    Wonder if you have tried this?

  10. AC0FP

    AC0FP Ham Member QRZ Page

    I haven't tried that specifically. I did remove power which I thought was supposed to clear memory.

    Anyway I am aware of the tune lock circuit and may give it or a similar circuit a try but I think I will try and reroute my widow line feed first this coming weekend.

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