The PAR End-Fedz (Par's spelling) is a Fuchs type antenna; an end fed 1/2 wave radiator.
Its advantage over shorter radiators is that it requires very little ground, if any, since it's fed at a voltage loop. Efficiency is not compromised by a mediocre ground as is so common with radiators 1/4 wave or less in length because virtually no current need flow into a ground system. If it's mounted vertically it will still have the induced ground losses all verticals have but, being half wave long means it can have the current loop some distance above the ground. If fully vertical the loop will be 1/4 wave away from the lossy earth, helping reduce induction losses. The disadvantage of a Fuchs is that one must decouple that high-impedance voltage loop at the feed point from the rig. Modern solid state gear is very unforgiving of even a little RF voltage floating around. That's part of what the matching network at the end must do as it transforms several thousand ohms impedance to 50 ohms. The matching network must also handle the extreme RF voltages involved at the voltage loop - often in the thousands of volts of RF - requiring component spacing and capacitors designed for those voltages. Notice the PAR antennas with relatively small matching units are strictly power-limited. Many compact solid state tuners won't handle those voltages or impedances. Old hamshack photos from the 20's and 30's often show a large coil/capacitor "tuner" mounted high on the shack wall, out of casual reach. That was the sort of tuner commonly used with the Fuchs antennas then (as well as with open wire feed for multiband doublets). Sometimes a Fuchs is called a "Zepp", but a Zepp offer as low impedance feed using 1/4 wavelength of open wire transmission line as an impedance transformer converting the very high impedance at the end of the 1/2 wave radiator to a low impedance at the transmitter. So a "Fuchs" can be thought of as a true Zepp without the feed line. I've not used a PAR design but I currently use a 130 foot homebrew Fuchs set up as an Inverted L with 40 feet vertical and 90 feet horizontal at my home QTH. It does a great job on 80-10 using an external tuner. The design works well on the harmonically-related Ham bands where it shows a high impedance at the end. As the frequency goes up, making it longer in wavelengths, the impedance at the feed point drops, making the voltages a bit less but still quite high. On other bands a Fuchs can be used as a simple random-length end fed wire if the matching network allows. Then a ground becomes more important, especially as the length drops to 1/4 wavelength or less. I use my Fuchs as a simple 1/4 wave end-fed wire on 160 with good results working against a counterpoise, but where it really shines is on 80 and the higher frequencies. Ron AC7AC -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Jim Brown Sent: Monday, March 02, 2009 1:32 PM To: [email protected] Subject: Re: [Elecraft] PAR endz-fed On Mon, 2 Mar 2009 10:16:27 -0800, Randy Cook wrote: >HOW MANY OF YOU ARE USING PAR ELECTRONICS END FEDS This is a VERY easy antenna to build. Why would anyone want to buy what they can build in an hour for a fraction of the cost? See http://audiosystemsgroup.com/NCDXACoaxChokesPPT.pdf One half of the dipole is a quarter-wavelength of wire, connected to the center conductor of the coax feedline. One quarter-wave from the end where the wire is connected you add a ferrite choke that functions as an "end insulator" for the coax, which makes the section of the coax between the wire and the choke the other half of the dipole. You do NOT apply a velocity factor when determining the length of the coax between the wire and the choke. If you're running 100W or less, the choke can be as simple as 10 turns of the coax around two 2.4-inch o.d. toroids, #31 or #43! I used much bigger chokes to run 1.5kW. For 20W or less, a single toroid is plenty. 73, Jim Brown K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
