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Putting a switch in a antenna tuner

Discussion in 'General Technical Questions and Answers' started by KI8FR, Nov 23, 2009.

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  1. KI8FR

    KI8FR Ham Member QRZ Page

    On my 75 meter dipole I have a low swr on most of the band. But when I go to the lower part of the band I need to tune it. I was thinking of putting a switch in my MFJ tuner to bypass it for the upper part of the band, and use the tuner for the lower part of it. I see in most tuners there are aluminum wires in it. Is there a reason for this?

    What I am asking is. Has any one tried this and does it work?

    Paul/ki8fr
     
  2. N5MOA

    N5MOA Subscriber QRZ Page

    I don't see why it wouldn't work, most tuners have a bypass setting on the antenna switch to do just that.

    Which tuner do you have?
     
  3. KI8FR

    KI8FR Ham Member QRZ Page

    Not sure. I amnot by it. It is a small one. They called it a moble on lol

    I will have to look and see what one it is when I get home.

    Paul
     
  4. KA8RAW

    KA8RAW Ham Member QRZ Page

    I just sold my Vectronics antenna tuner, and, I added a bypass switch in it, which worked very well. If I still had it, I would have gladly taken pictures of the conversion that I did.
     
  5. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    The wires might look like aluminum, but I guarantee they are not aluminum.

    They're tinned or plated copper wires.

    For sure.

    WB2WIK/6
     
  6. WA9SVD

    WA9SVD Ham Member QRZ Page

    Awwwww,

    There goes my theory that at least MFJ had finally come up with an easy way to allow soldering Copper to aluminium, or even aluminum:rolleyes: . DARN!
     
  7. K7MH

    K7MH Ham Member QRZ Page

    It has been mu experience that MFJ has a difficult time with soldering anything let alone something less than conventional!
    Don't most tuners have a bypass position?
     
    Last edited: Nov 24, 2009
  8. WA7KKP

    WA7KKP Ham Member QRZ Page

    Don't modify it . . .

    I'd just leave the tuner inline all the time on 75, and keep a crib sheet with the tuner settings for the low end (80 meters).

    Better yet, dump the coax, replace it with ladder line, and then you can use it anywhere with the antenna tuner.

    Coax is okay as long as the SWR is kept low. That's the advantage of ladder line -- you don't have to have a matched line for efficient power transfer. Just a good tuner.

    Gary WA7KKP
     
  9. 2E0JCA

    2E0JCA Ham Member QRZ Page

    Hi Paul,
    I'm guessing its an MFJ-971 with the nice brushed aluminium finish and cross needle meter. If so, i had one and its very annoying that it doesnt have a bypass switch, but a nice little tuner all the same. I looked at the schematic, which you can get from the MFJ site, and it looked easy enough to add a switch. I ended up selling it and getting the smaller 902 which does have a bypass, but no meter. Works fine with the built in meter on my 857 though.

    Cheers,
    James 2E0JCA
     
  10. KI8FR

    KI8FR Ham Member QRZ Page

    I was thinking of getting a new one with a switch in it. but this is a good tuner. I got a new tuner some years back from aes. It is a acer or something like that.. It had a meter in it and it worked like crap. Was a waist of 100 bucks. I did find out what the problem was with the thing and looked like a ezy fix. Just never got to it. That is why I was thinking of just putting a switch in the MFJ. If it did not work I put it back the way it was and call it good. I got this tuner in Dayton years back for 10 bucks. Ben a excellent tuner.
     
  11. VK2AKG

    VK2AKG Ham Member QRZ Page

    OT - soldering aluminium

    Soldering aluminium is easy - it's only the aluminium oxide that gives you grief. Just cleaning it in air is a waste of time because the oxide reforms almost instantly. The trick is to coat both the aluminium and a piece of steel wool or a brass brush with turps, WD-40 or light machine oil. You then remove the oxide layer _through_ the coating before soldering _through_ the coating. The function of the coating is to prevent the aluminium oxide reforming so don't remove it until you are finished.

    Ordinary 50:50 or 60:40 solder will work OK though I used to make my own "special mix" which made the job a little easier. I think my mix was 95% tin and 5% zinc but alas it is too long ago to recall with certainty, no doubt someone will sell something similar nowadays.

    73 Frank vk2akg
     
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