Tuner confusin

Discussion in 'General Technical Questions and Answers' started by KE0WXN, Dec 11, 2019.

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  1. KE0WXN

    KE0WXN Ham Member QRZ Page

    Please be merciful, I'm new to this. I was a ham in the ancient past and came back to the hobby late and I miss my old 'Elmer'.

    I got a new IC 7300, A vertical multi band antenna and a MFJ 939. I did my best to tune the antenna and get it up and working. I seem to do best on 20M and I am able to get it to work reasonably well. My issue is the automated antenna tuner and meter in the IC 7300. I get to a frequency and hit the MFJ tune button. It clicks and then lights a green SWR. I click the tune button on the 7300 and it shows 'tune'. If you check the meter and graph almost anything will show up. I went into the set section and tried auto and manual and get radically different SWR numbers. The MFJ manual and the ICOM manuals seem to have different answers.

    Oh BTW, this thing has an odor. I am never using more than 20 W because I am concerned that I smell output transistors (or is that old school?)

    I know that the two automatic systems are connected by the cable and I checked to see that MFJ sent the ICOM cable. What I can't figure out is a system that is reliable and a procedure order that is safe and effective.

    Any help out there?

  2. K7TRF

    K7TRF Premium Subscriber QRZ Page

    I'd probably start here. What multi-band vertical antenna are you running? What do you have for radials and what kind of match do you see when it's tuned for each band without any tuners in line?

    Normally you wouldn't need an external tuner to use a tuned vertical antenna except perhaps to stretch the SWR bandwidth on some bands. Is the vertical something with an adjustable loading coil or perhaps a trapped vertical? If the SWR without any automatic tuner in line is less than 2:1 on the frequencies you plan to use then there's no real reason for using the tuner. If it's not 2:1 or better then I guess the question is why the vertical isn't giving you a better match sans tuner but that depends a lot on what the antenna is and how you have it set up.

    In terms of the tuner and rig combo, do you hear the tuner going through its tuning sequence (relays clattering) as it attempts to achieve a match? If not then you may still have a cable or rig configuration problem. If you can get the tuner to go through a full tuning cycle then what kind of SWR does it settle to on various bands. I'm not sure what you meant by:
    Are you saying that the SWR is unstable and constantly changes even though the tuner has finished its tuning cycle? Or are you saying each time you run the full tuning cycle the tuner settles on a different solution and you see a different SWR? Either way, is that final SWR the tuner gives you after running a tuning cycle higher than 2:1?

    Do you have access to any kind of dummy load so that you can validate the rig and tuner are doing what they should without adding the extra complexity of antenna system problems? Some antenna problems like excessive common mode current from insufficient radials or bad contacts somewhere in the antenna system can lead to crazy jumpy SWR behavior and make it very difficult for any antenna tuner to find a stable match to what amounts to a moving target.

    If you can separate the antenna system from tuner issues at least in your initial testing you can figure out where the problems lie. A dummy load is one way to do that (and every ham shack should have one as they can help solve many RF issues) but you could also do something like build a relatively small and inexpensive 10m dipole (roughly 16 feet of any kind of wire and some coax, even 75 ohm TV coax to feed it) hang it up and test into that as that's likely a better behaved test antenna.
    Last edited: Dec 11, 2019
    KU4X and KD0CAC like this.
  3. KD0CAC

    KD0CAC Ham Member QRZ Page

    Checkout all of the above .

    But it reads like you are using one tuner . 7300 , into another , MFJ ?
    K7TRF likes this.
  4. K7TRF

    K7TRF Premium Subscriber QRZ Page

    I was wondering about that as well...
    KD0CAC likes this.
  5. NN6D

    NN6D Ham Member QRZ Page

    I don't miss my old elmer
    he was cranky
  6. KC9YGN

    KC9YGN Platinum Subscriber Platinum Subscriber QRZ Page

    Sam, here's what I think is happening: The 939 is an auto tuner that, I think, constantly monitors the SWR. It looks at the frequency you're using, looks at the impedance (SWR) and then automatically switches in and out various coils to change the impedance until it gets a reasonable SWR. This by itself works just fine, most of the time. If I remember right it automatically follows the transceiver's frequency and will activate even if you don't press the "tune" button manually if it senses something has changed.

    But now you're throwing a 2nd antenna tuner, the 7300's, into the mix, while the MFJ is still hooked into the system and active. The 7300's own tuner now starts looking for the "perfect" match by switching it's own coils in and out. The MFJ now sees that the impedance is changing as the 7300's tuner works, so it starts in trying to change the impedance to get a better match. The two of them end up in a sort of loop, fighting each other, each unable to actually get a solution to the problem because the other unit is constantly changing things to get a solution at the same time. Finally they give up and, well, heaven only knows what you'll end up with.

    Use one or the other, not both. Unless there is something wonky with your antenna and/or feed line, the 7300's internal tuner should be able to get a match without needing any help, so take the MFJ out of the line completely. Or if you prefer to use the MFJ, turn OFF the 7300's own internal tuner and just use the MFJ.
    Last edited: Dec 11, 2019
  7. N7WR

    N7WR Premium Subscriber QRZ Page

    I agree. Do not use the built in tuner in the 7300. Or use it and not the external MFJ
  8. W9KEY

    W9KEY XML Subscriber QRZ Page

    If you go looking for a "new" Elmer, try to find one with a good Antenna Analyzer. That would help verify your vertical is reasonably well set up.

    Then - as other above have mentioned, use one tuner or the other, but not both. The 7300's tuner should be easy to run - just push a button, and the rig will auto-tune. But such internal tuners are limited to about 3:1. The MFJ tuner (according to specs I just looked at) should be capable of up to 200 watts and a wider SWR match range. If you use it, just set the 7300's tuner to "off".
  9. W9WQA

    W9WQA Ham Member QRZ Page

    i dont think the 7300 will affect the mfj whick looks at the load on its outside,not at the input??
    i routinely use the internal WITH an ext sg230 on a wire antenna.sg is happy with <2:1, the 7300 tunes till it is happy and can output full power if needed..
    it is not a problem to use 2 tuners. some people just think so.!!
  10. N3PM

    N3PM Ham Member QRZ Page

    Sam, it seems the 7300 will recognize an external auto tuner and bypass the built in tuner when it's connected with the proper interface cable. For yours, it's the MFJ 5114I. This allows either tune button to initiate a cycle. My 7300 works this way with an LDG tuner.
    Check the jumpers in the MFJ, they may need repositioning.
    If your cabling and antenna are OK, maybe the interface cable isn't working properly.
    Mike N3PM
    WG8Z likes this.

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