MFJ-998RT tuner: radio interface?

Discussion in 'General Technical Questions and Answers' started by W5MT, Sep 28, 2019.

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  1. W5MT

    W5MT Ham Member QRZ Page

    Anyone know why the "Radio Interface" feature is not used in the MFJ-998RT Legal Limit tuner?

    Just borrowed the MFJ from a buddy to see if I want one. I run the DC separate from the coax because I previously used an Icom AH-4 (great remote tuner, albeit max 120W) and that control cable now supplies the DC for the MFJ.

    I read in the 998RT manual and observed on the schematic that circuits exist to support several manufacturers' radios that are capable of remote tuner use, as do other non-OEM tuners. This is a great idea and would be so much simpler for users with radios that support such tuners. I see in the schematic components for the feature; however, I have not looked at whether the parts are actually on the board in the 998RT. Sadly, the 998RT manual states "The Radio Interface function is not used in this tuner." Why is that?

    If the components are on the board in the tuner, has anyone tried to use the Radio Interface feature with any success? Just curious.

    I'm hesitant to do too much poking around or experimenting on my buddy's unit... or else it may by consequence become mine... hihi

    TU es 73
    Matt W5MT
  2. W4WTS

    W4WTS Premium Subscriber QRZ Page

    I have the MFJ998 and run the Kenwood interface the radio uses it's tuner between the radio and the amp, and the 998 is between the amp and the antenna. You have to go into the menu and enable it. It's called the radio Interface Menu, see page 21 in the users want to select ALINCO/ICOM for it to work....

    Mine is just a 998, not an RT.
  3. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Because MFJ marketed this remote tuner as a simple coax fed device that only needs a bias-T on the shack end and doesn't need an additional control cable. If you've looked at the schematic then you've likely also noticed that the actual circuit board is the same as they use on their shack tuner and supports a display board and up down C/L controls but those also aren't used when this board is used as a remote feed point tuner. That's just economy of scale to repurpose their shack tuner as a remote tuner without having to layout and support a completely different design.

    Sure, you may have already run a separate control cable to support your Icom tuner but for many hams contemplating a remote tuner purchase it's easier to just run power up the coax via a bias-T and not have to run additional cables. MFJ could have included the connectors to support rig interface for those that wanted to run the extra cable but that would have added parts and associated cost which isn't the kind of thing MFJ does very often.

    I suspect you'll find that all the components necessary to support vendor specific rig interfaces are actually on the PCB and the tuner only lacks the appropriate connectors. You could likely find a way to keep the unit waterproof and still connect the remote rig interface but personally I wouldn't go down that path unless it was actually my own tuner I was messing with.
  4. W5MT

    W5MT Ham Member QRZ Page

    Yes, I believe I looked at the manual of the 998 one time and the feature IS available on that model; not the 998RT per its manual.

    Tnx W5MT
  5. W5MT

    W5MT Ham Member QRZ Page

    There is what appears on the schematic as an RJ-11 or RJ-45 style connector on the board. You are correct, there is no connection from there to the outside. The pins on this connector go to the radio interface controls (+12, GND, TUNE START, COMPLETE).

    All of your comments make perfect sense wrt to MFJ hihi. Interestingly, there are parameters in the tuner you can change manually; however, you have to remove the cover and then access the display and control buttons within the tuner... and sometimes with RF applied hihi. For example, on 75m, the best it'll tune my wire is to an SWR of 1.9 (measured at the output of my amp), so it's probably a little worse at the antenna. The manual states, like most tuners, you can manually cycle through different L and C settings to see if you can "tweak" it in and I'm going to try that this weekend. On an LGC desktop auto tuner I used for a bit, you can make manual adjustments with it in the same fashion; it helped most but not all times... and not on 75m, so I'm curious to see what MFJ will do. My AL-811 says the output circuit will tune up to 2:1 and if need be, I'll be okay with that, but would prefer lesser of course.

    I personally would prefer to have the radio interface work. It's a one button push on my Icom (same as with the AH-4) and your done. Without it, I have to reduce my TX power to 20W, go to RTTY and transmit, wait for the tuner to finish, then run the power back up. Admittedly, it's not difficult, but I like one button approach much better as I'm used to that after having the AH-4 for 15 years.

    If I decide to buy my own 998RT or this one, only then would I make the mods.. hihi

    Good info!!
  6. WA7ARK

    WA7ARK Ham Member QRZ Page

    I am using the 'RT with a IC-7300. I have a variety of antennas and manual tuners, so already had a need for solving the "get the radio to put out 10W CW for tuning issue" even before I got the 'RT.

    Here is what I came up with:

    Push2Tune for the ICOM IC-7300

    Works great with just the biasT. I route the +12V to the biasT through a toggle switch to save power, and there are times when you need to get the remote tuner out of the way (it is bypassed automatically when power is removed).

    Here is a similar device for sale. I know nothing about it, except that it looks like the one I posted.
    Last edited: Sep 28, 2019
  7. W5MT

    W5MT Ham Member QRZ Page

    Thanks Mike, good info. Since I had the AH-4 control cable already in place, and I prefer to minimize unnecessary losses in the feed line (like bias Ts, long jumpers, adapters, etc. hihi), I put an old Heath HWA-202 PS on the cable and just turn the PS on and off as needed.

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