END-FED WIRE

 

The Alinco manual warns against using antenna wire length that is a multiple of 1/2 λ, as this will result in high voltages at the coupler (at resonance), and may be hard to to tune. The warning does not mention how close to 1/2 λ is "too close". Apparently, no velocity factor needs to be applied to this length...

 

INSERT 1/2 λ table

 

The table below shows the 1/2 λ limits for each band, assuming a +10% and -10% margin around each 1/2 λ value. Note that objects near the antenna can and will de-tune the antenna, i.e., change the effective wire length. Based on this table, there is no single wire length that satisfies the "no multiple of 1/2 λ" rule for 10-80m or 10-160m...

 

   1/2 λ limits Calculator  

Double left-click on the value in the "before" window and type in a new value. Do the same for the "after" window. Then click on "Calculate". You must have javascript enabled.

 

Note: when using the coupler with a dipole, 1/2 λ is actually a desired antenna length.

 

I want to put up as much wire as I can. Made a table. Table: no mention of velocity factor of the wire. Should there be? Based on what I can put up at my location, 16.3-18.5 m wire should be OK. TBV integer multiples Actual: 16.4 m, stranded #14 AWG copper hook-up wire (2 mm2), black THHN coated (Thermoplastic High Heat-resistant Nylon) from the Do-It-Yourself store.

 

CENTER POST WITH TEFLON TUBE

 

Bungee cords at ends, at ATC.

 

 

VERTICAL

 

Radio Shack 102 inch "CB Whip" (SKU 21-903). 2m6 long stainless steel whip. Good value for money ($21, mid-2011 pricing), 1/4 λ in the 27 MHz citizens band ("CB").

 

Extended to 4.6m with a 2m copper tube with 16mm OD. Nut mounted in top.

 

Cannot have an antenna installed (here: erect) permanently, so I decided to use a heavy-duty ratchet flagpole holder ("1 inch white cast aluminum multi-position bracket") to pivot the antenna out of view, when not used. I bought one for about $10 at Home depot, mid 2011 pricing (item #60754, brand: Valley Forge).

 

The flagpole holder in horizontal position

 

The flagpole holder in vertical position

 

Will be mounted right next to the coupler. The pergola is made of steel H-beams, and will serve as counterpoise for the coupler. So I cannot mount the vertical antenna directly onto it. Made a bracket out of aluminium (4mm thick, high-grade), and used a wooden block between the flag pole holder and this bracket.

 

Copper tubing: 16 mm OD. Pole holder: 1 inch (25.4 mm ID). Needed insert. Wooden vs epoxy casting, or combination? Plus "drain hole" for the wire.

 

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Bottom of the whip screwed into the cupper tube

before & after adding shrink-tube weather seal to the joint

 

Rugged enough for wind?

 

 

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Antenna coupler and vertical antenna installed

 

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RESULTS - PERFORMANCE

 

Compared to?

esp. 80 m?