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The MFJ-1935 Cobweb antenna review and on-air test

Discussion in 'Amateur Radio News' started by KJ4YZI, Nov 21, 2016.

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  1. KJ4YZI

    KJ4YZI Ham Member QRZ Page

    Just put this antenna together in 2 hours, and made some easy contacts on this weekend's November Sweeps. Check it out.
     
    K3RW, KM6DYO, M6VIE and 3 others like this.
  2. G0NKZ

    G0NKZ Premium Subscriber QRZ Page

    Cobweb looks good but looking now for comparison with vertical. G0NKZ.
     
  3. KK5JY

    KK5JY Ham Member QRZ Page

    The QRZ article title needs to be edited -- the proper part number appears to be MFJ-1835. Product link here: http://www.mfjenterprises.com/Product.php?productid=MFJ-1835

    This is a really neat antenna design. The compact construction of a hexbeam, but bidirectional like a dipole, and much, much lighter. My hexbeam weighs in at over 25#. The manual for this antenna says it is around 8#.

    I'm going to have to try one of these.
     
    Last edited: Nov 23, 2016
    KC9K and KC5HWB like this.
  4. HB9FIH

    HB9FIH Platinum Subscriber Platinum Subscriber QRZ Page

    Its easy to build one yourself.
    It runs very well. I v made and use them at qth ta3 with success. My is with cable (Aircell7) and 6m mast only 7 kg !
    See http://www.hb9fih.org/?p=p_195&sName=ta3--cobwebb-antenne-21.9.2015-...

    There are two different wirings.
    1.With dual cable (speaker cable) and gamma match (sometimes hard to tune, but needs no balun - no loss)
    (For tuning over the hole bands i use the sg237)
    2.With single wire, easy to tune but needs a balun (impedance transform)
     
  5. KJ4YZI

    KJ4YZI Ham Member QRZ Page

    Yes it's a typo i made. It is clearly the MFJ-1835
     
  6. K4CKF

    K4CKF Ham Member QRZ Page

    I was looking at this antenna also but noticed two different part numbers MFJ-1835 and MFJ-1835H. What is the defference?
     
    NX6ED likes this.
  7. KG0MN

    KG0MN Ham Member QRZ Page

    Is MFJ providing these items for review or are you paying for them out of pocket?
     
    KM1H likes this.
  8. NI0F

    NI0F Premium Subscriber QRZ Page

    The H suffix denotes a version that will take 1500 watts and costs a bit more, the non-H is only 300 watts.
     
    N0PLV and N9NSB like this.
  9. KO5AOK

    KO5AOK Ham Member QRZ Page

    Nice review video, thanks for doing this. Looks like a nice antenna to take on a road trip and do some portable work, or even at the home QTH for QRP experiments. Even the lower height got you some contacts. Might be good for NPOTA and similar quick trips.
    73, KG0UFO
     
  10. N7XGR

    N7XGR Ham Member QRZ Page

    Starting at the 45 second point of the video he mentions 5 horizontal square loops with 3-4 Db gain but with
    insulators opposite the feedpoint then this makes this like he mentions a folded fan dipole.
    If this was a full wave loop antenna it would be much larger. Since this is only a folded fan dipole
    I do not see any Db gain from it.

    YMMV

    Bruce N7XGR
     
  11. KI8W

    KI8W Ham Member QRZ Page

    Thinking about getting one of these but I would be a bit concerned what happens with an ice load. We get quite a few of those every winter. I also want to know if it needs any kind of rotator.
     
    Last edited: Nov 24, 2016
  12. K8JHR

    K8JHR Ham Member QRZ Page

    Nice video by an obviously nice guy, and yet...

    I do not believe this is a "loop" antenna, but a folded fan dipole, with five dipole wires connected at a common feed point. The far ends are spaced apart from each other with dielectric material and do not complete the loop.

    I do not believe this antenna provides "3-4 dbi gain" as claimed in the video. MFJ literature says it "packs a 3-4 dB gain advantage over ground-independent verticals" - which is a very different claim, because many ground-independent verticals show a substantial loss, and less than unity gain, compared with a dipole.

    Testing during a big domestic contest, when there are hundreds of high power stations with huge antennas on the air, does not provide a realistic indication of antenna performance. Almost any antenna will work during a big contest.

    I believe the tuning adjustment strips should be installed equally on both sides of each dipole - otherwise one side of the dipole will be longer than the other.

    Testing SWR on the rig by merely transmitting a sideband carrier is not a proper test protocol. It would be much better to show what happens when one transmits a 100 watt CW tone or at least have the technician speak. A sideband carrier with no voice data won't move the meter much.

    Just MY take... your mileage may vary ... I look forward to the direct A/B comparison with the vertical. / JR /
     
    KR3DX likes this.
  13. N7EKU

    N7EKU Ham Member QRZ Page

    Right,

    The cobbweb antenna is not a loop antenna, but a group of dipoles (fan dipole) with their wires bent into a square shape. There are questions on this forum almost every day about bending the wires of a dipole. This is just one that is really, really, bent! You get some advantages and disadvantages -- compared to a straight dipole -- when doing this:

    Cobbweb pluses:
    Omnidirectional so no worries about direction when errecting
    More gain when compared to the nulls of a dipole
    Takes one fourth of the linear space needed
    Needs only one vertical support

    Cobbweb minuses:
    Narrower bandwidth (covers less of the ham band with low SWR)
    Less gain compared to the main lobes of a dipole
    Ice/wind loading becomes more of an issue
    Must use a matching device due to low impedance at feedpoint (included in most designs)

    It's really a handy design for many small city lots. Not really anything unusual or strange, just what you get when you bend up a dipole. If I remember correctly the models I've seen for it, the heighth about ground issue (affecting angle of radiation) is still the same as for a regular dipole.

    73,


    Mark.
     
    KO4UVU and KR3DX like this.
  14. W8AAZ

    W8AAZ Ham Member QRZ Page

    Bet it would outperform a certain "half wave" mini vertical I had here once. Horizontal, probably less noise pickup. Well a square loop antenna worked well for me last summer on 6 meters so I guess I could carry over the same concept to the lower bands with this. No radials like a small vertical might need, single support and lightweight. Might finally be a practical way to get back onto the higher bands for me. Yea, ice and wind might be a factor, need to find more reviews. Does not cover the whole band, well a lot of the multiband verticals don't really, either. He did test it close to the ground. I bet that compared to a vertical, even moderate height increase might lower the pattern for better DX though. He needs to tell us how it works at say, 20 or 25 feet. Cause if you can afford a tower to put it up at a much higher height, you probably can afford a beam or something too.
     
  15. NX6ED

    NX6ED Ham Member QRZ Page

    My pet peave: The operator/assembler when testing the antenna neither listened first to the frequency before tuning nor did he identify himself (former is bad protocol and latter is a violation).
     

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