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Author Topic: Another QRP antenna experiment  (Read 7133 times)
W1JKA
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Posts: 1773




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« on: May 07, 2014, 10:58:43 AM »

This spring after 5 years of use I took my portable 20/30/40 meter QRP dipole which was 3 sets of radiator wires to a center insulator (no balun or tuner) and decided to just use the 40m radiators for all 3 bands by simply folding back excess wire on 20/30m alongside the 40m legs and held tight against with small plastic tie wraps which were adjusted for a tight thread fit and kept permanently on the 40m radiators.

Tuning was done in a small open wooded area (no RFI), 20/30m fold back points marked with paint. I took the SWR meter on the next two outings only and don't take it now. SWR results from 3 different locations, antenna 15-20 ft. high and both horizontal or inverted V set ups on all 3 bands were any where between 1:2-1 and 1:6-1 which is fine by me ( I'm not a perfect SWR nut) and performs as well as my previous version.

Pros: 1) Fast easy set up
         2) less wires and light
         3) Cheap or cost nothing to make
         4) No balun/tuner
         5) perform very well

Cons: 1) To some but not me: The 5 minutes it takes to lower antenna change band and haul back up. I know the daily/seasonal prop on these bands and will initially set up accordingly, other wise I will listen to all 3 bands on the 40m length, find the action and change if need be.

As I frequently camp/sail and operate QRP M/M from my 8 ft. sail dinghy "Kluster Duck" I'm looking forward to see how this antenna compares with the old version when set up on/near salt water when I cruise the Maine coast island chain this summer.




    
« Last Edit: May 07, 2014, 11:01:25 AM by W1JKA » Logged
KB1GMX
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Posts: 783




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« Reply #1 on: May 07, 2014, 06:24:34 PM »

My expectation is other than band changing there will be no difference other than it will be
lighter and less likely to get tangled up.

Dipole is a dipole, is a dipole.  In both cases it's a basic dipole and the parallel wire dipole has
only the convenience of no mechanical changes to get to another band.

It should work well.


Allison
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K8AXW
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Posts: 3905




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« Reply #2 on: May 07, 2014, 08:29:50 PM »

Great idea!!  Sometimes we can't see the forest because of the trees. Thanks for sharing.
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KL7CW
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Posts: 74




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« Reply #3 on: May 18, 2014, 05:31:10 PM »

Many QRP operators use a 40 meter inverted V. We isolate the 20and 30 meter,( and other sections ?) with small insulators and use clip leads, plugs, or switches to select which band we want. Sometimes I do not even need to lower my antenna to change bands, or at the most just drop the center part way down until I can reach the insulators. This scheme might be slightly quicker than your equally good idea of folding back unused portions.  Several years ago I bought a few lamp pull chain switches, with the thought of using them to isolate the 20 meter from the 40 meter section of a portable inverted V.  The untried idea was to just yank on each end of the dipole to toggle between 20 and 40 meters.  I have no idea if the pull chain switch is OK for QRP RF. (for sure it would not be an ideal end insulator.)  I think if the inverted V is made of small wire and tension and wind velocity are low the pull chain might work.  The 30 meter disconnect switch could probably be reached from the ground. Most rigs have some SWR indicator so it would be obvious if a leg was switched to a wrong band.  Might be a fun experiment...probably lots of theoretical reasons why this would not work.  The switch would get wet, so the idea would only be useful for temporary portable operation.
       Rick  KL7CW  Palmer, Alaska
 
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KB1GMX
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Posts: 783




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« Reply #4 on: May 22, 2014, 07:16:59 PM »

likely the pull-chain switches will work.  The constraint is not current but voltage and at 5W
the voltages will not be all that high.  Myself I'd use nylon cord rather than chain on them.

One scheme I'd seen was simple insulator (rings of 1" PVC pipe) and the bridging connection
was spade lug to its match in a connecter or left dangling from the insulator.  Simple and cheap.


Allison
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W1JKA
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Posts: 1773




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« Reply #5 on: May 23, 2014, 04:48:07 AM »

40-10 meter resonate portable dipole with small 3 way slide switches, Google Phil Silas AD5X antenna site.
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KL7CW
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Posts: 74




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« Reply #6 on: May 23, 2014, 12:37:36 PM »

My "pull chain" idea was not to have a separate pull string, but to attach the switch body to the up hill side of the wire and attach the "chain" through an insulator (if necessary) to the downhill side of the antenna leg.  Then wire the switch contacts to the wires.  My switches require a moderate amount of pull to cause a switch, so might work fine with light weight antennas.  You would only want to use one pull switch per antenna leg to isolate an upper band.  Other types of switches which would be easier to reach from the ground could control the lower sections.  This idea would not work with a fishing rod or kite pole...too much pull would be required, but might be fine with a tree or sturdy mast.  Again...just another crazy idea to try.  My pull switches are small and light weight...probably only an ounce or two....think I got mine at Home Depot or Lowes.
            Rick  KL7CW
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