Shortened 7Mhz Dipole

When looking around for a 40m diople, found this and built it I can say it works even if short!  I got a good match with my MFJ analyser and on QRP, worked around Europe ok.  I also heard VK/ZL!  And only at 30 feet as an inv Vee so if stuck for space try this.

To construct each side of the antenna proceed as follows. Cut a 10.25 metre length of 24/0.076 insulated wire, and a 160 mm length of 40 mm o.d plastic tubing ( white plumbers tubing). Measure a 2.75 portion of the wire and attach the wire to the plastic former. Wind 40 turns of the wire onto the plastic former, and firmly secure the end of the winding. Make the other half of the antenna in the same way. Attach the ends of the 2.57 metre sections to a suitable centre insulator, which should also mount the choke balun, connect the 50 ohm coax, then carefully waterproof the whole assembly.

The choke balun uses RG174AU coax and a 40mm Ferrite Toriod. Once the antenna is erected adjust it to resonance on 7.030Mhz (or wherever your fav 40m freg is!) by folding back the ends, and adjust the length to provide minimum SWR.

This could be made multiband by replacing the feed point with a 4:1 balun and feed with 50 Ω co-ax or directly with 300 Ω (or 450Ω) ribbon feeder to a balanced AMU or 4:1 then AMU. (update 8-09-10)
Article from SPRAT Issue 74 Spring 1993

Portable 2 Meter Slim Jim antenna using 300 Ohm Twinlead

In order to proceed with this project you need

* about 165 cm (64 inch) 300 Ohm twinlead cable
* RG-58 coax cable (RG-8, RG-213 might be too big for soldering), any length but keep it shorter than 7 meters for portable radio
* Soldering iron
* Wire cutter
* Connector to your Rig (usually BNC type or UHF Male)
* insulating tape

This is an ideal antenna for first timers to build. It is powerful yet simple to construct, once you get the hang of it you would certainly have no problem to construct other variants of Slim Jim antenna using different material.

This exercise would also prepare you in the world of Amateur Radio where real hams homebrew their own antennas.

Important Notes

* Make sure you solder the center conductor to the longest part of the antenna, and the outer conductor (braid) at the shorter side of the antenna
* If you use this on mobile rig, keep transmission power lower than 50watt to avoid the antenna from being burned away.
* Make sure the antenna is held straight for best transmission and reception. Best way to make sure of that is to hang the antenna at a higher place or strap it to PVC pipe or other non-conductive pole

Advantages of 300ohm Twinlead Slim Jim Antenna

1. Easy to construct
2. Has radiation angle almost parallel to the ground which makes your transmission goes farther than 5/8 or ground plane antennas
3. Wideband
4. Portable; Easy to carry, store and deployed
5. Can be use during emergency situation
6. Light and flexible