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Re: [loopantennas] Varactor tuned loop questions

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  • Chris Trask
    ... No reason why not, but your tuning bandwidth will be different than that of the original design. ... I would suggest adding an SPST relay across the first
    Message 1 of 12 , Jan 31, 2013
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      >
      >Hi folks - new to the group!
      >
      >I'm thinking of building the varactor tuned loop from Christ Trask's paper "A Simple Varactor-Tuned Loop Antenna Matching Network" in the Files section.
      >
      >I have a couple of questions:
      >
      >1) Is there any reason not to use a couple of 1SV149 diodes in place of the MVAM109s? The 1SV149s seem
      > to be more readily available!
      >

      No reason why not, but your tuning bandwidth will be different than that of the original design.

      >
      >2) Is there any need to take special precautions if the loop is positioned say, 20ft, from a Tx antenna
      > at a power level of 400W?
      >

      I would suggest adding an SPST relay across the first transformer on the varactor side, closing the contacts when transmitting. That much power at that distance could possibly damage the varactors.

      Chris
    • Steve
      My thanks to everyone who responded As a footnote, a packet of 1SV149s arrived today, they and appear to be working fine. I have implemented Chris idea of a
      Message 2 of 12 , Jan 31, 2013
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        My thanks to everyone who responded"

        As a footnote, a packet of 1SV149s arrived today, they and appear to be working fine. I have implemented Chris' idea of a relay for protection - it is driven from my station T/R line.

        Thanks again.
        Steve
      • Richard (Rick) Karlquist
        ... Please, where did you buy the 1SV149 s? Rick N6RK
        Message 3 of 12 , Jan 31, 2013
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          On 1/31/2013 11:52 AM, Steve wrote:
          > My thanks to everyone who responded"
          >
          > As a footnote, a packet of 1SV149s arrived today, they and appear to be
          > working fine. I have implemented Chris' idea of a relay for protection -

          Please, where did you buy the 1SV149's?

          Rick N6RK
        • Steve
          I bought here: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=121036971493&ssPageName=ADME:L:OC:GB:3160 Steve
          Message 4 of 12 , Feb 1, 2013
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            I bought here:
            http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=121036971493&ssPageName=ADME:L:OC:GB:3160

            Steve

            --- In loopantennas@yahoogroups.com, "Richard (Rick) Karlquist" wrote:

            >
            > Please, where did you buy the 1SV149's?
            >
            > Rick N6RK
            >
          • Chris Trask
            ... That is exceptionally cheap. Chris
            Message 5 of 12 , Feb 1, 2013
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            • Steve
              Really? 10 for $2.99 here:
              Message 6 of 12 , Feb 1, 2013
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                Really?

                10 for $2.99 here:
                http://www.ebay.co.uk/itm/10pcs-1SV149-ISV149-1SV-149-Varicap-Varactor-diodes-NEW-/200609638692?pt=LH_DefaultDomain_0&hash=item2eb5442924

                Regards,
                Steve

                --- In loopantennas@yahoogroups.com, Chris Trask wrote:
                >
                > That is exceptionally cheap.
                >
                > Chris
                >
              • Chris Trask
                ... I was thinking with regard to the NTE equivalent. This price is amazing. Didn t think that we would ever see affordable varactors of this range in a
                Message 7 of 12 , Feb 1, 2013
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                  >
                  >>
                  >> That is exceptionally cheap.
                  >>
                  >
                  >Really?
                  >
                  >10 for $2.99 here:
                  >http://www.ebay.co.uk/itm/10pcs-1SV149-ISV149-1SV-149-Varicap-Varactor-diodes-NEW-/200609638692?pt=LH_DefaultDomain_0&hash=item2eb5442924
                  >

                  I was thinking with regard to the NTE equivalent. This price is amazing. Didn't think that we would ever see affordable varactors of this range in a leaded package ever again. Certainly glad that this discussion came up as I can now look at other designs and not cringe at the cost of the varactors.

                  Chris

                  Chris
                • Steve
                  @ Chris, Slightly OT, but I thought I might also try your loop amplifier in a wideband design! I m struggling to find the MPS6521; would the BC550C be a
                  Message 8 of 12 , Feb 1, 2013
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                    @ Chris,

                    Slightly OT, but I thought I might also try your loop amplifier in a wideband design! I'm struggling to find the MPS6521; would the BC550C be a suitable replacement?

                    Also, I see no value for C18 in the schematic, but two figures given for C15; I presume C18 is the 47uF and C15 100nF?

                    Thanks,
                    Steve
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