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10660Re: [loopantennas] A bit OT: new delay line kit

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  • Andrew Ikin
    Jul 2, 2014
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      Hello Rick,
       
      I don’t really see a problem with Chavdar’s use of a binary delayline sequence because any small phase error is not likely to affect the array performance. That said; I would prefer the use of a potentiometer with a ADC for controlling the phase rather than using a PC com port.
       
      An alternative simplified design could use for example a 20ns delayline with 10 x 2ns tapes selected with 1 pole 10 way switch then buffered by a high z amp. so as not the load the delayline. Additional delay could relay selected prior to the tapped delay line.
       
      I used this scheme over 30 years ago with loop array and active dipole arrays in an effort to combat Soviet Jamming. To be honest it was a total waste of time; because simple two element arrays lack the required directivity when dealing with a multitude arrival angles at HF.
       
      73
       
      Andrew
       
       
       
      Sent: Wednesday, July 02, 2014 5:18 AM
      Subject: Re: [loopantennas] A bit OT: new delay line kit
       
       



      On 7/1/2014 8:44 PM, 'pu3hag.l@...' pu3hag.l@...
      [loopantennas] wrote:

      > Hi,
      >
      > Chavdar Levkov, LZ1AQ -
      who runs active-antenna.eu
      > <http://active-antenna.eu> - has
      included a
      > 2nd kit to his site: delay lines for phases antenna
      array.
      >
      > I have one of his loop amplifiers still to build. I admit
      I have zero
      > knowledge on delay lines and need to research a bit on this
      topic.
      >
      > -- pu3hag huelbe
      >

      Well, research this:

      http://www.n6rk.com/Lumped_LC_Delay_Networks.gif

      I published this in 2008 and I see that LZ1AQ's delay
      lines are virtually identical to the ones I described.
      Maybe he reinvented this stuff. I have an unpublished
      PC board design that uses jumpers exactly like the LZ1AQ
      board. However, I learned the hard way not to try to
      use a binary series of delays. Unless the delays are
      exact, there will be gaps in coverage and the delay
      you happen to need might be unrealizable. Instead, what I
      do is to use a so-called "Radix 1.5" series with ratios
      of: 1, 1.5, 2.25, 3.375, etc. instead of 1, 2, 4, 8 etc.
      This has a substantial overlap and allows for fairly
      sloppy tolerances. I got this idea from the ADC designers
      at Agilent who used Radix 1.5 to eliminate missing codes.
      They said everyone in the ADC community knows about this.
      Except, the variable delay line is analogous to a DAC
      instead of an ADC. Some principle though.

      Rick

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