Crushcraft R8 SWR-Problem

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by DL1DMS, Dec 7, 2020.

ad: L-HROutlet
ad: l-rl
ad: HRDLLC-2
ad: L-Geochron
ad: Left-2
ad: abrind-2
ad: Left-3
ad: MessiPaoloni-1
ad: L-MFJ
  1. DL1DMS

    DL1DMS Ham Member QRZ Page


    about 5....6 weeks ago I bought a new vertical HF Antenna (Crushcraft R8). We (My g/f and I) assembled it and a day later I mounted it on a small mast (only 250 cm at all, 150 cm in the roof truss, 100 cm outside) on the roof. The SWR was not perfect on all bands but it was usable so far.....

    This shows the resonance values after installing the antenna the 1st time.

    For safety reasons and for convenience I decided to add a tilting device to take the antenna down if needed. I ordered everything (massive U-Profiles made from stainless steel, Bolts, Screws.....) ,and built it by myself which took some days (maybe a week or so). After I was done I monted the tilting device on the 250 cm mast, added another peace of mast (100 cm) and mounted the antenna on that. So far so good... If there weren't the SWR which was not perfect on all bands.....

    I decided to shorten the elements for the 10, 12, 15 and 40m band to be more in the center of the band. I shortened the 10 and 12m band radiator for 2,5 cm, the 15 m band radiator for 5 cm and the 40 m band radiator for 10 cm. "Well done" i thought and went to my shack to meassure what I've done.

    I have recognized that the 30 m band is now completely unusable (resonance at 9.836 MHz) and the 20/17 m bands that had one resonance per band before has now only one resonance at 17.220 MHz.

    10 m is good now and I know how to adjust the radiators for 12, 15, and 40 m. That won't be a problem I hope. :) Unfortunately local laws don't allow us to use the antenna on 6m so I leave it out.

    This shows the resonance values after installin the tilting device and adjusting the radiators.

    This picture shows both lines in one graphic to compare it....

    The problem is the 30, the 20 and the 17 m band...
    I'm wondering where I can change the resonance for the 30 m band (There's nothing about it in the manual). Also I'm wondering why I now have only one resonance at 17.220 MHz for both (20/17m) bands and how to make it resonant on those bands again?

    I tried so but there was no effect.

    I appreciate every assistance.

    73's de DL1DMS
  2. AA5MT

    AA5MT Ham Member QRZ Page

  3. DL1DMS

    DL1DMS Ham Member QRZ Page

    Hello Tom,

    THX for the documents. I'll have a look on that after QRL and let u know if there's something helpful or not.

    73's de DL1DMS
  4. DL1DMS

    DL1DMS Ham Member QRZ Page

    Hello again

    last week I found some time to fix my 20m problem. Thought It would be pretty easy to do with the help of the documents. But it's not possible to shorten the length between point A and Point E without cutting the tube below Trap 1. And if I would cut there are some screws holdin' the hat capacity. I looked at the antenna carefully but there is absolutely no way to shorten it without destroying it. I also had a look into the trap. Honestly I was so desperated that I have removed some twists from the 20m coil but there were almost no changes. My resonance point is still at 14.020 MHz so the upper band (14.250 - 14.350) is not even usable with the internal tuner.

    The following shows the actual situation. Any help appreciated!! :)

    73 DL1DMS

  5. W9IQ

    W9IQ Ham Member QRZ Page

    A friendly reminder that a dip in SWR is rarely a resonant point.

    If you would like to identify points of resonance, use the complex impedance plot instead of an S11 (SWR/RL) plot. Then look for the frequencies where X is (nearly) zero.

    - Glenn W9IQ
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The first, original plot looked good to me on 20-17-15-12-10 meters and I wouldn't have done anything to change it.

    The very narrow BW dip on 40m just kHz below the band might have bothered me slightly, and the fairly lousy match on 30m might have also. But maybe not.

    From my experience with R8 antennas: First thing I'd do is use it on the air to make contacts, see how it "works" without fretting so much about the match. As an example, my only 60m antenna is a half-sloper, top fed against my tower, just cut per formula with no further adjustments or any attempt at matching.

    Its SWR at 5.4 MHz is about 5:1. Oh well. So, I went on the air using the internal ATU in every rig I have, which found a "match" at the source end just fine, and got some signal reports vs. other locals around here with other antennas.

    Every report I got was "You're just as strong as Joe," (or Clyde, or Stan, or anybody) in my local area when contacting stations 500-1000-1500 miles away.

    I never went back up to adjust anything, since it obviously works fine.:p

Share This Page