Egzactly Walter... that's the antenna arrangement I was thinking of back before DX on the "short waves" was discovered!
Thanks, 73, Ron AC7AC -----Original Message----- From: Elecraft [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Walter Underwood Sent: Friday, August 5, 2016 5:23 PM To: Elecraft Reflector Subject: Re: [Elecraft] ½ λ dipoles Some of the early “clothesline” antennas were a large capacity hat on a vertical. If the antenna has one vertical wire connected to all of the top wires, it is probably a capacity-loaded vertical. This Wikimedia image shows a top-loaded vertical. https://commons.wikimedia.org/wiki/File:Amateur_radio_T_antenna_1912.png <https://commons.wikimedia.org/wiki/File:Amateur_radio_T_antenna_1912.png> With longwave communication, a resonant antenna was not practical for most hams, whether horizontal or vertical. I certainly don’t have room for a half-wave for the 600 meter band. wunder K6WRU Walter Underwood CM87wj http://observer.wunderwood.org/ (my blog) > On Aug 5, 2016, at 4:53 PM, Don Wilhelm <donw...@embarqmail.com> wrote: > > Charlie, > > A bit of history --- > > Most of those ham antennas that used parallel wires were folded dipole > antennas - yes they were mostly 1/2 wavelength long. The feedpoint impedance > for that antenna is 300 ohms. Add a 3rd wire or a 4th and the impedance > increases. So to my mind, that was an attempt to match the feedline to the > antenna which in early days was open wire line which for normal spacing has a > characteristic impedance near 600 ohms. > By the time I became a ham, TV twinlead was common with a characteristic > impedance of 300 ohms. Many ham antennas were created using that twinlead. > A folded dipole was made from the twinlead and fed in the center with > additional twinlead serving as the feedline. > > With the migration to coax feedlines, those older techniques have faded from > memory, but those antenna *did* work just fine although many hams did not > really understand why. > > At that time we had PA tank circuits with swinging link coils and could match > most any impedance. The tuning sequence was to start with the link lightly > coupled to the PA inductor and then to "dip the plate" to resonance - then > slowly increase the coupling between the PA inductor and the antenna link to > increase the PA current. That was done in an iterative manner until the > plate current was at the desired point. > That process could match most any load that the antenna and feedline might > present to the transmitter. > > Then came television. Many ham transmitters were interfering with TV > reception, so transmitters became shielded devices, and the shift to coax > rather than open transmitters with the older parallel feedline connection > direct to the antenna slowly became a product of the past. Swinging links > and plug in coils inside a shielded enclosure were possible, but a PITA. > So the advent of the Pi-Network in ham transmitters was born. It allowed > band switching and could match a reasonable range of antenna impedance. The > shielded coax feedlines provided the chassis shield to be extended all the > way to the antenna feedpoint (or so the story goes, but that is not entirely > true). > > The bottom line of what I am trying to communicate is that much of ham radio > antennas, transmission lines and transmitter construction changed drastically > in the 1950s with the advent of television and that was done primarily to > reduce ham interference to TV viewing (TVI). > As an example of that effort, my first novice transmitter which I built from > a design in a 1955 ARRL Handbook was in a completely shielded enclosure and > used shielded wiring throughout with bypass capacitors at each end of the > shield wire. That included all the wiring, filaments and DC power circuits > and anything else. If you find a 1955 ARRL handbook it was the 75 watt > transmitter with a 5763 crystal oscillator and 6146 final included in that > book. Nostalgia urges me to again build that transmitter, but practical sense > says that it would be prohibitively expensive these days and some components > are no longer available. > > 73, > Don W3FPR > > On 8/5/2016 6:41 PM, Charlie T, K3ICH wrote: >> I'm curious as to when the concept of a ½ λ dipole became the norm? >> >> In other words, the idea of the current distribution as exists on a dipole. >> >> Early pictures of typical ham antennas looked more like a set of >> parallel clothesline wires. >> >> What I gather from reading early articles, it seemed that the more >> wire you had in the air, the better it would "capture" (and radiate) the >> signals. >> >> Feel free to reply directly if you don't want to clutter the forum. >> >> (k3ich at arrl dot net) >> >> > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net Please help support this email > list: http://www.qsl.net/donate.html Message delivered to > wun...@wunderwood.org ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to r...@elecraft.com ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
