Re: [sierra_wilderness_radio] Re: Portable Antennas
- A couple of salient points about 1/2 wave antennas, baluns, and end-feds.
There is no such thng as an "end-fed" with a counterpoise. i.e. Either an antenna is fed from one end or it is not, as the "counterpoise", when connected to a/the network (your antenna,rig, and tuner combination), **IS** a part of the antenna.
And yes, sometimes center fed antennas may require a balun if a particular performance (pattern) is desired when used with coax. Why ? .... because coax is a three terminal transmission line, and the outside of a coaxs can radiate depending on various factors. (The specific length of coax being a common reason for such radiation and the use of baluns to mitigate this effect being a "solution".) This coax radiation will most likely be a departure from the classic resonant dipole pattern. (BTW this change may be an enhancement or a detraction depending on your desires for such an antenna. But it is real and a contributing factor in the resulting radiation pattern. And baluns are a great way to control coax radiation.)
w9yaOn Sun, Feb 22, 2009 at 6:09 AM, Donald McBride <McBride_D@...> wrote:Hello Frank,RE: AntennasNothing is easier, as you know, than a simple half-wave dipolefed with coax, and I have several depending upon what portablerig I'm carrying to the field. However, my 25-year old 3-band"jumper dipole" is my favorite. With sections separated byinsulators and small alligator clips, it can be quickly set for 20,30 or 40 meters by just temporarily lowering the center supportslightly.Perhaps like you, I've experimented with balanced line-feddoublets and they certainly work, but coax is just so mucheasier to pack and deal with and doesn't require a balun.Another antenna you may also have tried is the "Dollar Special"found on the Internet at:While inflation has run that up to $2 these days, two packs ofDollar Store speaker wire can be turned into a three-bandend-fed with tuned counterpoise and still wrapped up fortransit in a plastic sandwich bag. I carry mine all the time incase something goes awry with my dipole, such as a brokenwire or forgotten whatchamacallit or whatever and haveworked the Ukraine with it from the park with my 2 watt SIERRA.Oh, and did I mention that all these antennas are "cheap"? <grin>... 72/73,... Don