Phasing antennas to reduce noise floor.

Discussion in 'Ham Radio Discussions' started by VK5FPAC, Dec 7, 2017.

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  1. VK5FPAC

    VK5FPAC Ham Member QRZ Page

    Phasing antennas to reduce noise floor (using an MFJ-1026).


    Ok, I have checked out many Youtube clips and forums using this item but it all seems very hit and miss! My antennas are visible on my BIO page here and I would be interested in any advice on how to get this up and running...

    ... cheers Bob
  2. AA7QQ

    AA7QQ Ham Member QRZ Page

    Download the manual. MFJ has it under documentation. Pretty neat. I have used one many times here in Vegas.

  3. VK5FPAC

    VK5FPAC Ham Member QRZ Page

    I have the printed manual...

    ...looking towards someone willing to share their experiences with this.
  4. KC8VWM

    KC8VWM Moderator Volunteer Moderator QRZ Page

    These require two antennas.

    Describe the other antenna you are using.

    They only work well if you are using an effective second antenna.
  5. VK5FPAC

    VK5FPAC Ham Member QRZ Page

    I have another matching RX only inverted 'L' offset at 180 degrees from main TX/RX inverted 'L' antenna.
    So two identical antennas facing away from each other.
  6. KC8VWM

    KC8VWM Moderator Volunteer Moderator QRZ Page

    Well you are all set then.

    So you have a good antenna, followed all the tuning directions described in the user manual and your MFJ-1026 is still not doing anything?
    VK5FPAC likes this.
  7. KQ9J

    KQ9J Premium Subscriber QRZ Page

    I have one of those and it works very well. With the onset of winter here my obnoxious 10 db over S9 buzz saw noise is back. It is something that comes on when it is below freezing outside; though I have the direction it is coming from established, I have never been able to track it down to the point source. Without the MFJ, the noise is impossible to tolerate and obliterates all but the strongest signals. With the MFJ, I can null the noise out.

    These gizmos work very well on a single noise source, as long as the receiving antenna is capable of picking up the noise at the same level as the main antenna, you can null it out. If you have a bunch of strong noise sources coming from different directions, not so much.

    You will have to readjust it as you move around between bands. This is due to the fact that the noise has to be at the same level on both antennas and this level will change as you move around. :)
    VK5FPAC and KC8VWM like this.
  8. W0PV

    W0PV Ham Member QRZ Page

    When you say "reduce (ambient random?) noise floor" it worries me. These devices are not useful for reducing dispersed natural lightning QRN, cosmic / digital pink noise, etc.

    They can be wonderful in reducing effects from relatively local POINT sources of repetitive impulse noise, like power-line or power-device QRM. However, even that can be problematic if you have more then one significant noise source.

    I have a JPS ANC-4. It can work well in a pinch (I would like to try the MFJ sometime too) . But be aware, there is NO FREE LUNCH! More then just the noise will be altered. So, NOTHING works as well as finding and extinguishing or mitigating the unwanted noise(s) at their source!

    This can seem daunting, but it can be done. And can be a very rewarding experience. Personal noise Fox-Hunting!

    Start within your own shack / house! Make sure its not some darn cheap wall-wart or other devices PS. Use a battery powered rcvr, even an AM BCB radio, hit the house mains CB off! If it goes quiet then each branch circuit gets tested.

    If no joy then start walking around. Switch to a VHF HT (set for AM mode) and Arrow beam if needed to zero in. When outside keep ears open for sound of arcing that corresponds with noise bursts.

    GO FIND IT !!

    VK5FPAC, N2EY, KK5JY and 1 other person like this.
  9. VK5FPAC

    VK5FPAC Ham Member QRZ Page

    It worked, well a bit!

    Dropped my noise floor on 80m by 4 signal strength points and got rid of a nasty 'wood pecker' on 15m.

    Not perfect nor quick but I guess once I get the antennas set up right this thing can be of great use.

    Why someone has not made this like an auto tuner is anyone's guess.

    Automation is the goal, any suggestions?
  10. K0RGR

    K0RGR XML Subscriber QRZ Page

    Noise blanker technology took a turn for the worse a few decades ago. Two U.S. companies, Collins and Drake, offered optional 'noise blanker' units for some of their rigs. The Collins unit worked particularly well by sampling the impulse noise on a different frequency - around 40 MHz as I recall. That sampled noise was then inverted, and fed back into the IF of the receiver out of phase, cancelling the noise impulses. The effect was pretty amazing. I had a friend with an S line receiver who had a terribly noisy powerline in his back yard. The noise would actually pin the S meter on his receiver, but when the noise blanker was switched on, it was as though the power line noise was switched off! I was very jealous of that setup for a long time.

    However, as the Japanese rigs started to flood the market, they were not to be outdone, so they, too, offered a 'noise blanker' function. These, however, were simply 'clippers' - very simple circuits that just clipped off the noise peaks. They really did nothing to eliminate the base noise, so these 'noise blankers' were pretty ineffective. They further evolved in an effort to counter the in-band over the horizon radars of the time (aka, 'the Woodpecker'). The superior Drake and Collins units couldn't touch the Woodpecker, in spite of their superior ability to eliminate noise.

    Now, I rarely find a noise blanker that's terribly effective on power line noise. I haven't tried the optional Ten Tec unit that sounded promising. Modern Noise reduction circuits can do a fair job, but still not as dramatic as the old Collins unit. However, the advent of IF output ports on popular rigs these days should open up the possibility of someone building an external unit that behaves like the old Collins unit.

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