Inspired by the well known “link dipole” I made a half wave version for my HyEndFed ( http://www.hyendcompany.nl/ ) that I use as a vertical with a fishing pole.
Instead of the original 10/20/40 mtr band wire with a coil near the top I also have a wire with link connectors for the bands 10/12/15/17 and 20 mtr. This wire is about 10 mtr long ( half wave on 20 mtr ) with 4 connector pairs on the right locations. Just open one connector pair and all the rest of the wire to the end is unused. Coupling to the rest of the wire is zero.
I used round ”FastOn“- crimp connectors, often used in cars. In open position they are held together with a strip of plastic with the wires in two holes. No extra strain release is needed.
If wanted you can add a 30, 40 and 80 mtr part as well.
The “10/20/40 mtr HyEndFed” box itself can be used on all frequencies between 10-80 mtr. ( not at 6 mtr ).
Normally I work vertical or with the wire as a slooper . I connect the top of the wire with a piece of hose to the mast and protect the bottom end of the mast with the bottom part of a small drinking bottle. To avoid bending of the thin top end of the fishing pole I attach the coil or the wire to the pole at about 2 mtr down with a piece of Velcro ( hook-and-loop fastener ).
In a field test I made the SWR on all bands < 1,2 in the middle of the band, and as a result I can work on all bands without a tuner now. In my case all wires are about 3% shorter than the formula for a ½ wave antenna ( half lambda -5%) in the middle of the band.
On the 10 mtr band the radiation pattern is now much better ( it is now a ½ wave antenna ). The original antenna works as 1 ( one ) wave antenna on this band ( 10 mtr wire before the coil ), resulting in a very bad radiation pattern.
Advantage is also that I have all bands now and if you make a full ½ wave version ( without a coil ) for the 40 mtr band the gain of the antenna is higher.
Small disadvantage: I have to lower the mast and change a jumper connector to go to another band.
Of course you can also do this modification using the original 40 mtr coil to shorten the antenna. Just add the coil and the 1,85 mtr top wire at the top end of your home made 10-20 mtr link antenna.
I use a 10/20/40m HyEndfed antenna that is modified on my request by the producer Ron PA3RK. The coil connection is better protected and inside the coil now. The original connection is already very strong but not strong enough for frequent SOTA activity. The black Fritzel insulator is not placed to reduce size. The wingnut is replaced by a 4 mm banana plug chassis mount. My antenna wire has a fork, but a stripped wire can be attached also.
In my new antenna Ron used DX-wire Premium wire (http://www.dx-wire.de/brit/dxpe.htm ). This is very rigid ( with a stainless steel inner wire ). For portable activity this is very good. Just roll it up, no reel needed, it fact you can not bend it that much.
After 2 sub zero SOTA holidays and a some PAFF expeditions I am very happy with the modifications made by Ron.
See some pictures on my site: http://www.smitzeewolde.nl/index.php/hardware/hardware-endfed-antenna/
After our summer holiday ( in OE ? + HA ? )
I hope to report you about my new link antenna in SOTA use. So be prepared for tests on higher bands.
I hope some Endfed antenna users have a use for my modification.