AX-1 whip antenna
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I have been trying to come up with a antenna for use in an apartment with
only limited success. I have now set up the Elecraft AX-1 antenna and it seems to play well with my K3 indoors with the antenna placed in a window supported by a folding camera tripod. One caveat is that there seems to be significant feedline RF so a 1:1 isolation transformer near the antenna feed point is an absolute requirement. Without the transformer, even 1 watt transmissions caused various nasty computer gremlins when using digital modes. My apartment no longer needs to be a maze of wires and switches - many thanks to Elecraft for this excellent product. Jobst AC0LP ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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I wonder what would happen if you moved the 1:1 choke to the other end of
your feedline (closer to your K3)? -Steve On Fri, Dec 6, 2019, 11:41 AM Jobst Vandrey <[hidden email]> wrote: > I have been trying to come up with a antenna for use in an apartment with > only limited success. I have now set up the Elecraft AX-1 antenna and it > seems to play well with my K3 indoors with the antenna placed in a window > supported by a folding camera tripod. > > One caveat is that there seems to be significant feedline RF so a 1:1 > isolation transformer near the antenna feed point is an absolute > requirement. Without the transformer, even 1 watt transmissions caused > various nasty computer gremlins when using digital modes. > > My apartment no longer needs to be a maze of wires and switches - many > thanks to Elecraft for this excellent product. > > Jobst > AC0LP > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [hidden email] > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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In most applications there should be 2 RF chokes. The first RF choke
should be at the antenna feed point, and a 2nd RF choke at the radio. I find that Jim, K9YC has done excellent work in this regard. This is a case where many hams and balun companies only go at the problem "half baked". Thus if one is using a balun at the top side, one needs to be used at the bottom side as well. In this case the word "balun" is implying a 1:1 RF choke. 73 Bob, K4TAX On 12/6/2019 2:27 PM, Steve Hull wrote: > I wonder what would happen if you moved the 1:1 choke to the other end of > your feedline (closer to your K3)? > > -Steve > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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In reply to this post by Steve Hull
Sorry - I don't have very short jumpers available right now for that test -
the actual setup has 2 feet of coax between the antenna and the isolation transformer followed by 4 feet of coax to the K3 connector. This configuration works fine when testing in FT8 mode at 20 watts on 20 meters and also on 40 meters (when using the AEX1 extender). Jobst AC0LP On Fri, Dec 6, 2019 at 3:27 PM Steve Hull <[hidden email]> wrote: > I wonder what would happen if you moved the 1:1 choke to the other end of > your feedline (closer to your K3)? > > -Steve > > On Fri, Dec 6, 2019, 11:41 AM Jobst Vandrey <[hidden email]> wrote: > >> I have been trying to come up with a antenna for use in an apartment with >> only limited success. I have now set up the Elecraft AX-1 antenna and it >> seems to play well with my K3 indoors with the antenna placed in a window >> supported by a folding camera tripod. >> >> One caveat is that there seems to be significant feedline RF so a 1:1 >> isolation transformer near the antenna feed point is an absolute >> requirement. Without the transformer, even 1 watt transmissions caused >> various nasty computer gremlins when using digital modes. >> >> My apartment no longer needs to be a maze of wires and switches - many >> thanks to Elecraft for this excellent product. >> >> Jobst >> AC0LP >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> Message delivered to [hidden email] >> > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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In reply to this post by Steve Hull
Of course there is considerable feedline RF -- the feedline is acting as
a counterpoise, carrying return current from the antenna. The problem is that the AX-1 is intended for use hand-portable rigs like the KX3 running battery power CW/SSB. Your attempted use of it as a fixed antenna and with an attached computer is an un-natural act. :) The solution to your problem has multiple components. First, add wires to the coax shield at the antenna to act as a counterpoise. Second, add a SERIOUS common mode choke at the feedpoint to keep RF off the coax. http://k9yc.com/2018Cookbook.pdf Third, carefully bond together the chassis of every piece of equipment in the shack that is interconnected. http://k9yc.com/GroundingAndAudio.pdf An even better solution is to use one or more antenna better suited to your setup. A quarter-wave wire connected to the center conductor and another connected to the shield makes a fine antenna; if your K3 has the tuner, an antenna cut for 30M will work on 20 and 40; one cut for 20 will work on 30 and 17. A choke is needed at the feedpoint (where those two wires are connected). All the wiring in your station acts as a receiving antenna for the equipment, so when your transmitting antenna is close to that wiring, it WILL act as a receiving antenna and dump it into your equipment. The solution to that is 1) bonding, as noted above AND 2) ferrite chokes on that wiring in you station. For those chokes, follow the recommendations on pages 9-10 of this applications note. http://k9yc.com/KillingReceiveNoise.pdf Finally, if you don't already own them, buy a copy of the ARRL Handbook and the ARRL Antenna Book and study the relevant sections on antennas. Both are updated every 2-4 years, but the changes are a small fraction of the content, so a used copy is plenty good enough. Ask around your local ham club -- it's very likely you'll find a ham willing to sell one. 73, Jim K9YC On 12/6/2019 12:27 PM, Steve Hull wrote: > I wonder what would happen if you moved the 1:1 choke to the other end of > your feedline (closer to your K3)? > > -Steve > > On Fri, Dec 6, 2019, 11:41 AM Jobst Vandrey <[hidden email]> wrote: > >> I have been trying to come up with a antenna for use in an apartment with >> only limited success. I have now set up the Elecraft AX-1 antenna and it >> seems to play well with my K3 indoors with the antenna placed in a window >> supported by a folding camera tripod. >> >> One caveat is that there seems to be significant feedline RF so a 1:1 >> isolation transformer near the antenna feed point is an absolute >> requirement. Without the transformer, even 1 watt transmissions caused >> various nasty computer gremlins when using digital modes. >> >> My apartment no longer needs to be a maze of wires and switches - many >> thanks to Elecraft for this excellent product. >> >> Jobst >> AC0LP >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> Message delivered to [hidden email] >> > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [hidden email] > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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In reply to this post by Jobst Vandrey-2
With only 6 feet of coax between the rig and the antenna, you've probably
done about all you can do. Proximity is your main problem now. I'd look at the possibility of getting your antenna outside, even if you need to disguise it somehow. Lyn WØLEN -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Jobst Vandrey Sent: Friday, December 06, 2019 3:16 PM To: Steve Hull Cc: Elecraft Reflector Subject: Re: [Elecraft] AX-1 whip antenna Sorry - I don't have very short jumpers available right now for that test - the actual setup has 2 feet of coax between the antenna and the isolation transformer followed by 4 feet of coax to the K3 connector. This configuration works fine when testing in FT8 mode at 20 watts on 20 meters and also on 40 meters (when using the AEX1 extender). Jobst AC0LP On Fri, Dec 6, 2019 at 3:27 PM Steve Hull <[hidden email]> wrote: > I wonder what would happen if you moved the 1:1 choke to the other end of > your feedline (closer to your K3)? > > -Steve > > On Fri, Dec 6, 2019, 11:41 AM Jobst Vandrey <[hidden email]> wrote: > >> I have been trying to come up with a antenna for use in an apartment with >> only limited success. I have now set up the Elecraft AX-1 antenna and it >> seems to play well with my K3 indoors with the antenna placed in a >> supported by a folding camera tripod. >> >> One caveat is that there seems to be significant feedline RF so a 1:1 >> isolation transformer near the antenna feed point is an absolute >> requirement. Without the transformer, even 1 watt transmissions caused >> various nasty computer gremlins when using digital modes. >> >> My apartment no longer needs to be a maze of wires and switches - many >> thanks to Elecraft for this excellent product. >> >> Jobst >> AC0LP >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> Message delivered to [hidden email] >> > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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