Endfed QRP 1/2 Wave Antennas for Fieldday and Emergency
|Over the years there have been hundreds of antenna designs, maybe even thousands. These antennas are usually fed from the center for various reasons. Mostly because of feed line matching. The problem is that with a center fed antenna it's hard to erect, especially in a hurry. An endfed version of a half(1/2) wave antenna is the answer, but the end is high impedance and difficult to match to a 50 ohm feed line. We have solved this problem. Our matching network is parallel(shunt) fed into an "L" network that handles the matching with ease. This parallel(shunt) fed matching network version gives a very wide bandwidth antenna with very low SWR. For example, you can usually cover the entire 20 meter ham band with ease, with no tuner. Our antennas are half(1/2) wavelength dipoles fed from the end. This makes the perfect antenna for quick setup of portable QRP, field day, or emergency operation. Our antennas are rated very conservatively for 100 Watts max transmitter power.|
|Mounting this type of endfed antenna is easy. Use a slingshot with some monofilament fishing line tied to a rock or just throw the fishing line over a tree limb to support one end of the antenna wire. The matching network end of the antenna can be draped sloping toward the ground and connected to the radio with a short piece of coax. Try to not let it touch limbs of grass, as this could effect your swr. The closer your antenna is to the ground the higher your transmitted radiation angle will be. Remember, the closer to the ground the distributed capacitance along the wire combined with end effect will lower the resonant frequency of the antenna.
Our endfed half(1/2) wave antennas can be mounted horizontally, vertically, sloping, or as some sort of inverted "L". Most QRP work can be done with the sloping setup. You can even connect the antenna directly to the radio without coax. We have tried this and it works, but we don't recommend it.
Each matching network on the end of our antennas is encapsulated in a potting material to keep out moisture.
We tested this encapsulation by submerging one of our antennas in a bucket of water for a week, then put it up and made contacts on 20 meters without even drying it off.
The antenna still had very low SWR and preformed beautifully.
These antennas weigh about half(1/2) a pound and are very durable. The opposite end of the antenna has a small loop soldered into it for easy attachment to monofilament fishing lines etc. The antenna wire is #16 gauge stranded TFFN copper, with a black vinyl jacket. The SO-239 connector is high quality Silver/Teflon. These antennas and their network is all black and are very "Stealthy". Although these antennas are great for portable applications they work well as a home station PSK or Digital modes antenna since they are so easily hidden.
On vacation trips or when traveling and staying in hotels, get a top floor, Take a small transceiver and one of these endfed antennas with you in a backpack. Hang the antenna over a balcony of your hotel room. You will be amazed what you can do with a half(1/2) wave vertical endfed antenna hanging off a 20th floor hotel balcony on 20 Meters with very low power. You can run such low power that you can power the radio with a wall wart. We have worked other ham operators all over the world with these antennas, in all kinds of weather, with great results.
Try one of our portable antennas, we believe you will like our antenna design it as much as we do.