New to me MFJ-998

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by WT4W, Feb 26, 2021.

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  1. WT4W

    WT4W Ham Member QRZ Page

    I just received a pre-owned MFJ-998 and have a couple of questions.

    When I first powered it up I had it run a self diagnostic and it came back with a "Wakeup Fail" fault. I had to walk away for a while to deal with something else, came back an hour or so later and re-ran the self diagnostic and this time everything was fine. Since then I've had it match all my antennas across the respective bands and it seems to be working perfectly.

    SO...... does anyone have any suggestions as to what that "Wakeup Fault" alarm was all about? I've been searching but so far haven't found a good answer.

    ALSO, how do those of you with MFJ-998s use them in conjunction with an amp? Full Auto mode? Semi Auto? I have an FT-920 and an AL-811H amp and yes, I have the amp keying line wired through the MFJ-998. Do you simply press 'Tune" when you change frequencies by a certain amount (in conjunction with sending it RF)? Turn the drive down to below 30 watts and then press "Tune"?

    I'm just trying to figure out in my mind the best compromise between convenience and being kind to the radio and amp.
  2. W9FL

    W9FL Ham Member QRZ Page

    You should never tune with the amp engaged.

    I also have a MFJ 998, and always press the operate/ standby switch on the amp to standby, before I tune.

    If you have the amp keying line through the tuner like you say, it should prevent the amp from engaging. I have my amp wired that way, but I don't want to take a chance with it working correctly every time, so I switch to standby on the amp.

    Lots of damage can occur to the amp, and/or the tuner if you key the amp while tuning.

    I also run the tuner in semi-auto, so that it does not auto retune with the amp keyed. The tuner should prevent that with the keying line through the tuner, but again, I am not taking a chance.

    As far as the "wake up fault", if it only occurred the one time, I wouldn't be concerned. Electronics can be finicky, and a random fault from time to time can probably be ignored.

    I had purchased a used 993B tuner, and it was acting weird the first several times I tried it. I did the full reset, and it was fine after that. I beleive there are some latching relays that could change state during shipping, and possibly cause a fault when the tuner is powered up.

    Edited to add:
    My amp and tuner is run with an IC-7300, so I press tune on the 7300, with the amp in standby, and the rig drops down to 10 watts for tuning
    Last edited: Feb 26, 2021
    AK5B and W9WQA like this.
  3. WA7ARK

    WA7ARK Ham Member QRZ Page

    With the remote '998RT, I cannot see the display, nor can I use an interface cable. The only "remote controls" I have is DC Power On/Off, 10W CW to "tune", 800W after tuning is complete.

    Turning off the DC power resets the device so that it is "bypassed", so cannot be damaged by high power on a frequency it wasn't expecting.
    When DC power is turned on, it comes on in the "bypass" mode.

    Applying <20W of carrier at some specific frequency causes a "retune". I use my homebrew "Push-2-Tune" to control that step.

    If it has seen that frequency before, it sets up its relays within one second, and is ready for high RF power.
    If it hasn't seen that frequency before, or if you switched to a "different" antenna, the auto tuning cycle could take as long as ~5sec.

    The only feedback I get during the tuning cycle is to watch an in-line SWR meter. If that settles to a low SWR, I can stop sending it 10W of RF, and can begin transmitting at high power.

    On the frequencies where the antenna is close enough (that is most frequencies for my loop), and it needs no help from the remote tuner, I just switch off the DC power to the tuner and send ~850W through it direct to the antenna.

    I tell you all this, because even if the tuner is sitting on your desk, the steps may be automated via an interface cable to the radio/amp, but the sequence will be the same.
  4. W9WQA

    W9WQA Ham Member QRZ Page

    tnx guys, i havnt used my amp thru my 998rt so im following this.
    want to be sure not to allow amp xmit when tuning...

    oh, my 998 is open on a shelf above my desk so i can access controls
  5. WA7ARK

    WA7ARK Ham Member QRZ Page

    ...Mine is 55ft up my tower. It has a remote coax relay between its output and two different antennas (loop and dipole) that it can tune or not... Both antennas are "balanced", so each has its own ferrite balun between the coax relay and the feedpoint of antenna. The tuner is located within 18inches from the feedpoint of both antennas.

    This is a great set up. It gives me nearly instantaneous QSY access to any ham frequency from 1.8 to 29MHz. The loop is used for the lower HF bands. The dipole is focused above 17m. The final SWR anywhere in that frequency range is <~1.7.
    N1VAU and W9FL like this.

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