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Re: LOOP AMPLIFIER

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  • john
    Hi Brian, the aluminium is simply a standard size strip of about 25mm x 3mm x 3m long. Will post a photo in the next few days. Imagine a piece of plastic pipe
    Message 1 of 10 , Jun 6, 2013
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      Hi Brian, the aluminium is simply a standard size strip of about 25mm x 3mm x 3m long. Will post a photo in the next few days. Imagine a piece of plastic pipe bent in a circle with each end secured in a 'T piece'. the aluminium strip is placed in the pipe before bending it around ie it is inside the pipe and bends along with it. Make sure connection wires come out through small holes drilled in the joiner. Connect one to each end of the strip, drill a small hole in each end of the arms of the T. Feed one wire from the inside to the outside, secure that end of the pipe in the T piece, bend the other end around into a circle, feed the other wire connection out through the hole on the other side then secure the pipe into the fitting.

      At this point you should have a length of plastic pipe bent into a circle with both ends secured by the T. Inside is a flat aluminium strip with a wire connected to each end coming out through small holes drilled into each arm of the T. That is your loop ready to connect to an enclosure with the electronics inside. It should be easy to use standard fittings to mount it on a support.

      All the pieces were just standard fittings from the hardware store's plumbing section. Total cost was maybe $25 and the whole thing is light and robust. Add LZ1AQ's loop amp and some CAT5 cable and I have a wellbrooke equivalent for maybe a third the cost of importing one. This is a great recieve antenna and has the advantage that I can knock down the local pest with a sharp null.

      Cheers, John
    • brian nsl
      John, Thank you for the response to my query, most kind. Your 25mm x 3mm flat strip I make equivalent to the surface area of an 18mm dia tube in RF skin terms
      Message 2 of 10 , Jun 6, 2013
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        John,
                Thank you for the response to my query, most kind.
        Your 25mm x 3mm flat strip I make equivalent to the surface area of
        an 18mm dia tube in RF skin terms which is about the same diameter
        as Welbrook use for the ALA-1530 !!!!
        Certainly our local DIY warehouse sells strip in 3m long lengths so
         will check out the cross sections available.
        From your clear description assembly sounds straightforward,
        the secret being not to lose the wire tail hi!
        As a matter of interest I had similar thoughts on using a 3ft dia plastic
        ' Hula Hoop ' with  rolled up turkey strength cooking foil as the core
        these are just the correct dia to fit into PVC 18mm electrical conduit
        fittings like ' T's, junction boxes, elbows etc ' which has the advantage
        of being much stronger than PVC water pipe.
        To date I have never  heard of anyone who has taken a Wellbrook ALA-1530
        apart !!!!! 
        I will let you know how I fare with my version of the loop.
        My particular interest is NDB and 28 mhz beacon monitoring.
        Your comments on nulling the local ' pest ' out is of much interest
        as I have 349.5 khz - Liverpool just 8 miles away, a real pain !!!!!
                                                  Regards,
                                                       72, Brian, G├śNSL.
        ----- Original Message -----
        From: john
        Sent: Thursday, June 06, 2013 1:02 PM
        Subject: [loopantennas] Re: LOOP AMPLIFIER

         
      • Andrew Ikin
        Brian wrote on June 6. Your 25mm x 3mm flat strip I make equivalent to the surface area of an 18mm dia tube in RF skin terms which is about the same diameter
        Message 3 of 10 , Jun 7, 2013
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          Brian wrote on June 6.
           
           
          "Your 25mm x 3mm flat strip I make equivalent to the surface area of
          an 18mm dia tube in RF skin terms which is about the same diameter
          as Welbrook use for the ALA-1530 !!!!"
           
           
          Brian,
           
          The loop amplifier in question has a very low input impedance, hence there will be a miss-match at MF and HF when using a loop with the above dimensions. Whilst this may not be an issue for just nullinng out a pest. There will be noticeable loss in s/n compared to Pixel and Wellbrook loops that use higher input impedance amplifiers.
           
          A very low input z amp. requires a much lower reactance loop. This is not easy to achieve whilst maintaining a reasonable capture area.
           
          Earlier this year I received updated Calibration data for the LFL1010 ( same amp as the 1530, but a much lower input z ) and compared it to the ALA1530. The net result was an approx. 10dB improvement is sensitivity at MF and HF with the higher input z ALA1530.
           
          Kind regards
           
          Andrew
           
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