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Re: Question on MFJ - 1789 Loop Antenna for SWL

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  • vbifyz
    In my experience, the main advantage of any loop is the ability to NULL the interference by rotating the loop (and maybe also tilting it). Indeed, randomly
    Message 1 of 6 , Mar 5 8:56 AM
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      In my experience, the main advantage of any loop is the ability to NULL the interference by rotating the loop (and maybe also tilting it). Indeed, randomly placed loop outputs as much interference as a random wire.
      Unfortunately, the desired orientation is band dependent, so a remotely controlled tuned loop requires two motors, one for tuning and one for rotation.

      73, Mike

      --- In loopantennas@yahoogroups.com, "qrpbear" <qrpbear@...> wrote:
      >
      > Lou,
      >
      > Before spending the money on a commercial loop antenna I suggest you try making a tuned loop out of about 10' of coax and a dual section BC band variable cap. It may well prove to be an eye-opener to you. Tuned loops, contrary to popular misconception, are NOT inherently immune to electrical interference... they are just as prone to it as a dipole or random wire in the same environment. The main attraction to a tuned loop is its narrow bandwidth which acts like a sharply tuned preselector ahead of the rf stage of your receiver. Tuned loops are also strongly influenced by objects in their near vicinity (esp. within 1 to 2 loop diameters radius).
      >
      > 73,
      >
      > 'Bear' NH7SR
      >
      > --- In loopantennas@yahoogroups.com, "n2pkt" <n2pkt@> wrote:
      > >
      > >
      > > I was thinking of purchasing the MFJ-1786 Loop Antenna to use for
      > > Shortwave Listening (in addition) to having it as my primary amateur
      > > radio antenna. I want to use it in my attic which is about 50 foot up on
      > > a high elevation. My present dipole grabs a lot of static from
      > > electrical sources. I thought this antenna would react similiar to
      > > Shortwave Magnetic Loop Antenna Pixel RF Pro 1B. Is this an option that
      > > I shoild explore? It is an expensive one, but I would not mind the
      > > investment if I could work DX as well as bring in weak stations on
      > > Shortwave "without" anymore static. I would appreciate any comments or
      > > suggestions! de Lou N2PKT
      > >
      >
    • n2pkt
      ... Thank you both for your replies, If the Loop is still acceptable to static and other interference. I may look into better dipole systems or maybe try the
      Message 2 of 6 , Mar 6 6:15 PM
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        --- In loopantennas@yahoogroups.com, "vbifyz" <3ym3ym@...> wrote:
        >
        > In my experience, the main advantage of any loop is the ability to NULL the interference by rotating the loop (and maybe also tilting it). Indeed, randomly placed loop outputs as much interference as a random wire.
        > Unfortunately, the desired orientation is band dependent, so a remotely controlled tuned loop requires two motors, one for tuning and one for rotation.
        >
        > 73, Mike
        >
        > --- In loopantennas@yahoogroups.com, "qrpbear" <qrpbear@> wrote:
        > >
        > > Lou,
        > >
        > > Before spending the money on a commercial loop antenna I suggest you try making a tuned loop out of about 10' of coax and a dual section BC band variable cap. It may well prove to be an eye-opener to you. Tuned loops, contrary to popular misconception, are NOT inherently immune to electrical interference... they are just as prone to it as a dipole or random wire in the same environment. The main attraction to a tuned loop is its narrow bandwidth which acts like a sharply tuned preselector ahead of the rf stage of your receiver. Tuned loops are also strongly influenced by objects in their near vicinity (esp. within 1 to 2 loop diameters radius).
        > >
        > > 73,
        > >
        > > 'Bear' NH7SR
        > >
        Thank you both for your replies, If the Loop is still acceptable to static and other interference. I may look into better dipole systems
        or maybe try the homebrew loop if I can locate some instructions.
        For now, I will continue to look around for a better system. Thanks again! Lou N2PKT
      • the_dalcassian
        Hi Lou, I have purchased the MFJ 1786 & the Remote Controller (Necessary), I am delighted with it. Have worked the USA & Argentina on 5W at -20DB ... on JT65A.
        Message 3 of 6 , Mar 9 7:38 AM
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          Hi Lou,

          I have purchased the MFJ 1786 & the Remote Controller (Necessary), I am delighted with it. Have worked the USA & Argentina on 5W at -20DB ... on JT65A. It is perfect for the digital modes as there is not much changing of frequency. I have mine at 15 foot above the ground (Outside) mounted horizontally. It will soon be at 35 feet mounted Horizontally in that polarization the nulls are vertical i.e. like wheel hub. That way I dont need a rotator. Anything of frequency by a small amount it does not pick up So it is very quite and pulls in anything I need when tuned. I suggest you keep a Dipole for general listening and then once decided just where to operate switch to the Mag Loop. Using the Digi modes as I do there is not so much jumping around as most of my contact are on spot frequencies. The MAG Loop is very selective and should significantly reduce your noise problem.


          Kind Regards Rodger (G8HLH)

          --- In loopantennas@yahoogroups.com, "n2pkt" <n2pkt@...> wrote:
          >
          >
          > I was thinking of purchasing the MFJ-1786 Loop Antenna to use for
          > Shortwave Listening (in addition) to having it as my primary amateur
          > radio antenna. I want to use it in my attic which is about 50 foot up on
          > a high elevation. My present dipole grabs a lot of static from
          > electrical sources. I thought this antenna would react similiar to
          > Shortwave Magnetic Loop Antenna Pixel RF Pro 1B. Is this an option that
          > I shoild explore? It is an expensive one, but I would not mind the
          > investment if I could work DX as well as bring in weak stations on
          > Shortwave "without" anymore static. I would appreciate any comments or
          > suggestions! de Lou N2PKT
          >
        • William Hein
          I recently moved to a new QTH and my shack here is mostly underground thus this superb directional low band rx antenna, which can sit on your rig or
          Message 4 of 6 , Mar 11 4:05 PM
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            I recently moved to a new QTH and my "shack" here is mostly underground thus this superb directional low band rx antenna, which can sit on your rig or operating desk, is no longer suitable for my situation and is therefore for sale.

            It is the latest and greatest version - the QUANTUM QX LOOP v2.0+ from Radio Plus Electronics - and includes plug in head units for three bands:

                 Long wave (160 - 530 kHz)
                 Medium wave (530 - 1700+ kHz)
                 Tropical band (1.8 - 6.2 MHz)

            Easy to null QRM and peak weak signals by rotating or tilting the ferrite head unit which feeds a double balanced 40+ dB JFET/MOSFET preamp.  Q-Multiplication allows super tight tuning.  Runs on 9 - 15 VDC thru 2.5mm miniplug or 9 VDC battery.

            More info:


            Cost over $400 new and is still in EX condition.  Will sell for $299 plus shipping via USPS, UPS or FedEx (your choice) or you pick up near Grand Junction CO.

            Non-smoking shack.  PayPal preferred but personal check OK with delay for clearance.  Can send photo on request.

            73
            Bill


            William Hein, AA7XT
            ex-AA4XT, NT1Y, AA6TT, KC6EDP

            Blog   AA7XT.com

            ARRL, CSVHF & AMSAT Life Member
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            Tel   +1 (970) 628-5120
            Email   Bill.AA7XT@...
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