NEED GUIDANCE - POSSIBLE RF

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K1KTF, Mar 4, 2018.

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  1. K1KTF

    K1KTF Ham Member QRZ Page

    A9980FCF-5625-4F2F-BB67-1F6F85E39AD7.jpeg F24A1DF5-B28A-4A97-9C9C-F5F63AD04FFF.jpeg
    Hi Friends:

    First I must confess I’m not technically smart, hence my post to you all.

    Recently I have been unable to tune my G5RV w/ my MFJ Tuner. No equipment changes and my G5RV has been up and working fine for (at least) 6 years w/out any trouble.

    Recently when I tune I can’t get the “reflected” and “forward” to set to “zero”. I checked the ground connections but have not examined the ladder line nor got up to check the antenna connections. I’m also using a Balun as well.

    Any guidance you can provide would be greatly appreciated.

    Thanks + 73! Steve - K1KTF
     
  2. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Does this happen on only one band or has the tuning behavior of the antenna changed on all HF bands that you normally use?

    In the case of a G5RV or similar (e.g. G5RV junior, ZS6BKW, etc.) I'd start troubleshooting by determining the 'natural' SWR of the antenna with the tuner in bypass mode. Do this at low transmit power as it's pretty normal to see natural SWR in the 5:1 to 10:1 range for these antennas but you should see distinct SWR dips on at least a few of the HF ham bands.

    For instance a typical full sized G5RV will show an SWR dip down to around 5:1 or less somewhere in the 20m band, a G5RV junior should show similar behavior somewhere in the 10m band. If you don't see any natural SWR dips across the HF bands then there's something fundamental wrong with your antenna. It could be an open connection somewhere, it could be a faulty balun, perhaps a cracked wire in the balanced feed line matching section or even a tree branch or something resting on the antenna wire. But the antenna should show distinct SWR dips in several of the HF ham bands as the tuner should just be cleaning up the slightly high SWR, not matching a completely random antenna wire.

    An antenna analyzer is ideal for this as it lets you make wide SWR sweeps and see dips well outside of the licensed ham bands but using your rig at low transmit power and making multiple SWR measurements per band can show you if the antenna is behaving anywhere near normally. You can Google G5RV SWR curves (or whatever variation you have) to see what the natural SWR curves for these antennas should look like and compare your measurements to those curves.

    BTW, if you do collect the natural antenna SWR data, keep it somewhere so you can refer to it in the future if you have similar troubles.

    If the natural SWR curves seem reasonable then you might look into your tuner. Typical problems with roller inductor tuners include oxidation or arcing spots on the roller inductor that lead to flaky inductor settings and unstable tuning. You can clean roller inductors with isopropyl alchohol if that's part of your troubles.
     
    Last edited: Mar 4, 2018
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The "forward" and "reflected" should never be zero, or you'd have no indication of anything at all.

    The objective is for reflected to be as close to zero as possible, while the forward to be the highest reading possible, simultaneously.

    The photo you posted shows an SWR of about 2.3:1, which is higher than desired but not terribly high.
     
    NH7RO likes this.
  4. WA3QGD

    WA3QGD Ham Member QRZ Page

    Compare with a known good jumper thru the tuner and start to eliminate the things before finding the loose,broken corroded or low resistance twist way up on an antennae thats refusing to come down and the little weeny insulator is flashed over. Or roller inductor a bit unhappy and needs to be gently set upon the numbers before hitting it with Modulated RF.
     
  5. KM4DYX

    KM4DYX XML Subscriber QRZ Page

    Winter weather can be tough on antenna systems. If that balun is exposed I'd take a hard look at it. And all connections.

    73,
    Al
     
    W8IXI likes this.
  6. W8IXI

    W8IXI Platinum Subscriber Platinum Subscriber QRZ Page

    That's good advice and I would only add that winter can also be tough on an rf ground, whatever it may be.
     
  7. K1KTF

    K1KTF Ham Member QRZ Page

    About a week ago when I was tuning up for CW, the SWR meter was very erratic making the needles go up/down quickly. Typically it's very easy for me to tune up w/ a nice 2:1. I took the lid off the MFJ and it looked in great shape. I cleaned it and fired it up again but no luck. Still erratic SWR meter. Again, I have NOT been up to the G5RV in quite a few years to examine the connections and balun. As soon as winter leaves I plan on getting back up there to take a closer look. FYI - We in southern CT have had some crazy weather this season w/ high winds, rain and yes snow. Thank you once again for your help. Much appreciated. 73 - Steve (K1KTF)
     
  8. K1KTF

    K1KTF Ham Member QRZ Page

    I have NOT been up to the dipole in years but we had a challenging winter w/ high winds, rain and snow. I have not examined the dipole connections and balun in years. I never thought a balun would ever go bad but thanks for your insight to check it out. Much appreciated. 73 - Steve (K1KTF)
     
  9. KB2WVO

    KB2WVO Ham Member QRZ Page

    do you have another tuner ? does the radio have onboard tuner? can you try tunning without that mfj tuner you have. borrow one?
    if you were a lil closer i could stop by. but iam in albany..
    this might help find issue. without goin up a ladder or roof ..

     

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