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Re: Half Loop Mag Mobile Antenna

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  • Gian
    Hi All, thanks for your replies. I am looking for a half mag loop to be installed over a car roofrack. Yes, I understand the car will become modified.
    Message 1 of 17 , Jun 18, 2013
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      Hi All,

      thanks for your replies.

      I am looking for a half mag loop to be installed over a car roofrack. Yes, I understand the car will become modified.

      Certainly these kind of antennas have not the best performance but maybe not wortse than a very short mobile antenna positioned at 45° over the car roof or like the one in the QST article.

      My basic questions are:

      1) How is the capacitor value calculated and the minimum required voltage

      2) what should be the minimum width of the half mirror side

      3) what it will happen to the rf current over the car roof?

      I have found several NVIS groups in yahoo. I enrolled in one nott too large, but the majorities have a very few members.

      Best 73

      Gian
      I7SWX



      --- In loopantennas@yahoogroups.com, Andy <ai.egrps@...> wrote:
      >
      > Gian <i7swx@...> wrote:
      >
      > > I am looking for a project/guidelines to homebrew a mobile half a loop HF
      > > antenna for emergency communications, to be mounted over a car roof.
      >
      > There are some antennas like that mentioned occasionally on the [NVIS]
      > Yahoo!group.
      >
      > Because they are electrically small on the lower HF bands, and close
      > to the ground, they tend to be rather inefficient. But if you need to
      > operate mobile on those bands, it is an option to consider.
      >
      > The commercial versions tend to be very expensive. Perhaps more than
      > a top-of-the-line radio would cost.
      >
      > There are occasional links to pictures of homemade versions, usually
      > without much detail. Radiation resistance tends to be low, so good
      > bonding to the roof/vehicle is crucial. Don't think of it as mounting
      > an antenna on your car; think of it as modifying your car to
      > accommodate the new addition.
      >
      > Andy
      >
    • Andy
      ... The main NVIS group is simply NVIS . It has well over 1000 members. It is not listed in the Yahoogroups directory (a signup group is listed instead,
      Message 2 of 17 , Jun 18, 2013
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        Gian <i7swx@...> wrote:

        > I have found several NVIS groups in yahoo. I enrolled in one nott
        > too large, but the majorities have a very few members.

        The main NVIS group is simply "NVIS". It has well over 1000 members.
        It is not listed in the Yahoogroups directory (a signup group is
        listed instead, making it a 2-step process), but you can go directly
        to the group. Just substitute the word "NVIS" in the URL for any
        other Yahoogroup's name.

        Andy
      • Craig Palmer KF5JYZ
        just use yahoo’s own search engine. go to your groups page where all your yahoo groups are listed and above them you’ll find a search box. pick a group
        Message 3 of 17 , Jun 18, 2013
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          just use yahoo’s own search engine. go to your groups page where all your yahoo groups are listed and above them you’ll find a search box. pick a group that has lots of folks and they are active ,unless all you want is to look into there files n links.
           
          Craig
           
          From: Andy
          Sent: Tuesday, June 18, 2013 11:22 PM
          Subject: Re: [loopantennas] Re: Half Loop Mag Mobile Antenna
           
           

          Gian <mailto:i7swx%40yahoo.com> wrote:

          > I have found several NVIS groups in yahoo. I enrolled in one
          nott
          > too large, but the majorities have a very few members.

          The main NVIS group is simply "NVIS". It has well over 1000 members.
          It is not listed in the Yahoogroups directory (a signup group is
          listed instead, making it a 2-step process), but you can go directly
          to the group. Just substitute the word "NVIS" in the URL for any
          other Yahoogroup's name.

          Andy

          No virus found in this message.
          Checked by AVG - www.avg.com
          Version: 2013.0.3345 / Virus Database: 3199/6421 - Release Date: 06/18/13

        • Gian
          Hi Andy, thanks for your additional info. Is the group the following? NVIS-NearVerticalIncidentSkywave@yahoogroups.com I have sent the mail requesting
          Message 4 of 17 , Jun 19, 2013
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            Hi Andy,

            thanks for your additional info.

            Is the group the following?

            NVIS-NearVerticalIncidentSkywave@yahoogroups.com

            I have sent the mail requesting membership.

            73

            Gian
            I7SWX

            --- In loopantennas@yahoogroups.com, Andy <ai.egrps@...> wrote:
            >
            > Gian <i7swx@...> wrote:
            >
            > > I have found several NVIS groups in yahoo. I enrolled in one nott
            > > too large, but the majorities have a very few members.
            >
            > The main NVIS group is simply "NVIS". It has well over 1000 members.
            > It is not listed in the Yahoogroups directory (a signup group is
            > listed instead, making it a 2-step process), but you can go directly
            > to the group. Just substitute the word "NVIS" in the URL for any
            > other Yahoogroup's name.
            >
            > Andy
            >
          • Andy
            ... That is the sign-up group, not the real one. It will get you there ... eventually ... if you follow all the steps. You can bypass that step by going
            Message 5 of 17 , Jun 19, 2013
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              > Is the group the following?
              >
              > NVIS-NearVerticalIncidentSkywave@yahoogroups.com

              That is the "sign-up" group, not the real one. It will get you there
              ... eventually ... if you follow all the steps.

              You can bypass that step by going directly to the NVIS group itself,
              which is named simply "NVIS" instead of
              "NVIS-NearVerticalIncidentSkywave".

              (The reason for the multi-step process is to try to keep spam-bots
              from joining the "real" group.)

              Here are a few other (smaller, less active) NVIS-specific groups I know about:

              NWNVIS
              HFNVIS
              NVIS-Antennas
              International_NVIS_Association

              These are all Yahoo!groups.

              Andy
            • Andy
              A number of years ago, somewhere on the NVIS yahoogroup ... either on the group s site itself or in links to other sites ... there were pictures of a couple
              Message 6 of 17 , Jun 19, 2013
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                A number of years ago, somewhere on the "NVIS" yahoogroup ... either
                on the group's site itself or in links to other sites ... there were
                pictures of a couple of vehicles with half-loop antennas welded on.
                Patricia Gibbons, one of the group's founders, who passed away a few
                years ago, had pictures of hers. IIRC she used an SGC antenna tuner
                at the feedpoint.

                I don't recall seeing much in the way of theory or math.

                Andy
              • Gian
                Hi All, thanks for your feedbacks. THe NVIS request via mail, as suggested on the group did not work out, I got delivery error. Yes, I have seen groups witha
                Message 7 of 17 , Jun 21, 2013
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                  Hi All,

                  thanks for your feedbacks. THe NVIS request via mail, as suggested on the group did not work out, I got delivery error.

                  Yes, I have seen groups witha few peopleand not active. There is one group with over 10000 members ...too many but I will try there.

                  What I may try is to build an antenna with mechanical measures that will not be critiocal for cars roof and fiddle around it with a normal capacitor and use an antenna analyser, than, if the results are similar to a standard magloop I can go ahead. We can try with a qrp rtx if it work on tx too.

                  Best 73

                  Gian
                  I7SWX


                  --- In loopantennas@yahoogroups.com, Andy <ai.egrps@...> wrote:
                  >
                  > > Is the group the following?
                  > >
                  > > NVIS-NearVerticalIncidentSkywave@yahoogroups.com
                  >
                  > That is the "sign-up" group, not the real one. It will get you there
                  > ... eventually ... if you follow all the steps.
                  >
                  > You can bypass that step by going directly to the NVIS group itself,
                  > which is named simply "NVIS" instead of
                  > "NVIS-NearVerticalIncidentSkywave".
                  >
                  > (The reason for the multi-step process is to try to keep spam-bots
                  > from joining the "real" group.)
                  >
                  > Here are a few other (smaller, less active) NVIS-specific groups I know about:
                  >
                  > NWNVIS
                  > HFNVIS
                  > NVIS-Antennas
                  > International_NVIS_Association
                  >
                  > These are all Yahoo!groups.
                  >
                  > Andy
                  >
                • Andy
                  ... got delivery error. Try again! If you got a delivery error, it probably means it was sent to the wrong address. The address for subscribing to the NVIS
                  Message 8 of 17 , Jun 21, 2013
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                    Gian <i7swx@...> wrote:

                    > THe NVIS request via mail, as suggested on the group did not work out, I got delivery error.

                    Try again!  If you got a delivery error, it probably means it was sent to the wrong address.  The address for subscribing to the NVIS group should be:

                      NVIS-subscribe (at) yahoogroups.com

                    substituting the '@' symbol for the "(at)".  (I wrote it that way because Yahoo sometimes obscures email addresses within group messages.)

                    If you prefer to subscribe via the web, go to http://groups.yahoo.com/group/NVIS/join but you will need a Yahoo account to do that.

                    Regards,
                    Andy

                  • va3ae
                    If you have not seen this already it might provide food for thought. 73 de va3ae
                    Message 9 of 17 , Jun 22, 2013
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                      If you have not seen this already it might provide food for thought.
                      <http://www.laud.no/la6nca/loop/>

                      73 de va3ae
                    • Gian
                      Thanks for your rely. Yes, I did visit that site. The only problem is to understand how the half a loop works, i.e. what happen to RF currents un the mirror
                      Message 10 of 17 , Jun 24, 2013
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                        Thanks for your rely.

                        Yes, I did visit that site. The only problem is to understand how the half a loop works, i.e. what happen to RF currents un the mirror part of the loop and on the car real roof.

                        I will try to figure out the capacitor formula from the 14-30MHz example.

                        Thanks and best 73

                        Gian
                        I7SWX

                        --- In loopantennas@yahoogroups.com, "va3ae" <va3ae@...> wrote:
                        >
                        > If you have not seen this already it might provide food for thought.
                        > <http://www.laud.no/la6nca/loop/>
                        >
                        > 73 de va3ae
                        >
                      • Andy
                        ... For a half loop that connects to the roof on both ends, at the very least you have the loop current itself which completes its circuit via the roof. There
                        Message 11 of 17 , Jun 24, 2013
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                          Gian <i7swx@...> wrote:

                          > ... i.e. what happen to RF currents un the mirror part of the loop and on
                          > the car real roof.

                          For a half loop that connects to the roof on both ends, at the very
                          least you have the loop current itself which completes its circuit via
                          the roof. There would be some spreading out of the current in the
                          roof, depending on frequency, I suppose.

                          Many mobile loops are complete loops that happen to rest slightly
                          above the roof. That's a good question what happens in the roof in
                          that case. I bet it depends a lot on loop orientation. Most of these
                          small mobile loops are vertically oriented, but I have seen horizontal
                          loops above the roof too. It would seem like the roof causes a
                          "shorted turn" that is close coupled to the loop, which is probably
                          not good.

                          Regards,
                          Andy
                        • Gian
                          Hi Andy, ... I have a two bars roof rack across it (add-on). Would it be necessary to connect the loop mirror side to it or isolate it as strong current may
                          Message 12 of 17 , Jun 26, 2013
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                            Hi Andy,

                            --- In loopantennas@yahoogroups.com, Andy <ai.egrps@...> wrote:
                            >
                            > Gian <i7swx@...> wrote:
                            >
                            > > ... i.e. what happen to RF currents un the mirror part of the loop and on
                            > > the car real roof.
                            >
                            > For a half loop that connects to the roof on both ends, at the very
                            > least you have the loop current itself which completes its circuit via
                            > the roof. There would be some spreading out of the current in the
                            > roof, depending on frequency, I suppose.

                            >
                            > Many mobile loops are complete loops that happen to rest slightly
                            > above the roof. That's a good question what happens in the roof in
                            > that case. I bet it depends a lot on loop orientation. Most of these
                            > small mobile loops are vertically oriented, but I have seen horizontal
                            > loops above the roof too. It would seem like the roof causes a
                            > "shorted turn" that is close coupled to the loop, which is probably
                            > not good.

                            I have a two bars roof rack across it (add-on). Would it be necessary to connect the loop mirror side to it or isolate it as strong current may spread ???


                            Best 73

                            Gian
                            >
                            > Regards,
                            > Andy
                            >
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