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Ham Radio Articles

Emergency Communications, Alternative Communications, Radio Wave Propagation, Electronics Engineering, Antennas, Field Operations, & More.
smartphone with rtl-sdr dongle & magnetic loop antenna
Lost In The Forest

The story of a man lost deep in the forest at night facing imminent danger. He embarks on a new journey in advanced radio direction finding (fox hunting) & hacking new ways to find his way to safety.

radio station in back of jeep
DoD Crossband Test

A comprehensive guide to the equipment used in a remote location for military communications during the annual DoD crossband test.

portable solar cart for emergency power
Solar Cart

A solar power station for emergency power. This cart powered the entire radio station as well as lighting for 48 hours during a remote field expedition. Directly after the event it was used to jump start a vehicle.

slingshot horizontal dipole antenna
Slingshot Horizontal Dipole Antenna

A dipole antenna that deploys by slingshot between two tall trees.

Slingshot Horizontal Dipole Antenna

slingshot horizontal dipole antenna
Dipole antenna & components needed to deploy it.

This is a relatively simple & straight forward project made from easy to source components. This particular antenna is cut for 40 meters, but it could be cut for any band. I use this antenna for all HF bands utilizing a tuner, bandpass filter, or tank circuit depending on the situation, but 40 meter CW was the initial purpose for designing & building it.

horizontal dipole antenna feedpoint
Antenna Feed Point

The feed point is constructed of 1/2" schedule 40 PVC. A tee, three caps, & a short length of pipe to connect them is all that's necessary. Stainless steel eye hooks are installed in two of the caps with nuts & lock washers prior to assembly with PVC glue. A BNC connector is installed in the other cap. Before assembly, all three caps were partially filled with epoxy resin & allowed to cure over night (water proof). An eye hook in the top of the tee allows for hanging the feed point if necessary. I have never had the need for this yet. 

balun
Balun
balun & BNC connector
Balun & BNC Connector

The balun was determined by calculation, not trial & error, but the antenna performs quite exceptionally without a tuner on 40 meters. The ends of both sides of the wire antenna (which is #10awg THHN stranded copper) enter the PVC through drilled holes. They are soldered to the BNC connector prior to assembly with glue. Strain relief is provided by looping the wires through the eye hooks & crimping with an aluminum cable connector as shown in the photo of the entire feed point earlier.

PVC insulator at end of dipole wire
End Insulator

The ends of both sides of the antenna are looped & crimped around a PVC insulator.

fishing reel that mounts to slingshot
Fishing Reel Slingshot Mount
slingshot with fishing reel attached
Slingshot & Fishing Reel

The fishing reel mounts to the slingshot by simply holding it in place. A PVC tee split down the middle with a hacksaw facilitates a fast easy setup. The tee fits snuggly. The slingshot is used to shoot a 1oz lead egg sinker to carry the fishing line over a high tree branch.

paracord
Paracord

Two long lengths of paracord are needed. Once the fishing line has been deployed over a high tree branch, it is used to pull the length of paracord over. The paracord will then be used to raise the antenna & stretch it high in the air between two trees. Rather than tying the paracord to something solid after the antenna is up, a firewood log or stone of appropriate weight hanging a couple feet off the ground allows the trees to blow in the wind without causing any problems.

coaxial cable
50 Ohm Coaxial Cable

Any good quality low loss coax will work well. It all depends on how high the antenna is & how far away the transmitter must be. I prefer BNC connectors for simplicity because BNC connectors are easily adaptable to any other type of connector, allowing me to use this antenna for as many different applications as possible. 

KG5EVY is a guest contributor on this site.
copyright KG5EVY

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