A bit of trivia... When the antenna/tower at KDKA was replaced in 1994, the legs of the old antenna were cut into thin cross sections, encased in clear plastic with a station medallion and sold for charity to Children's Hospital of Pittsburgh during their annual Christmas Fundraiser. It's a nice conversation piece.
73, Cliff K3LL/6 -----Original Message----- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Gmail Sent: Tuesday, September 11, 2018 4:24 PM To: elecraft@mailman.qth.net Subject: [Elecraft] Franklin antennas KDKA, Pittsburgh, still has a Franklin, they are not a center fed vertical. both the bottom and top sections are end fed. The purpose is to lower angle of radiation and reduce skywave and selective fading. KDKA has a motorized capacitor on the top section. Both stations have extensive ground systems that would not be needed if they were dipoles. KDs antenna was replaced in 1994. Still a Franklin as changing the antenna would have required a power reduction with the “ratchet rule”. Ray W8LYJ Formerly with Group W Engineering, owner of both stations until recently. http://www.durenberger.com/documents/KDKANEWTOWER.pdf Sent from my iPad > > > Message: 1 > Date: Sun, 9 Sep 2018 15:48:48 -0700 > From: Fred Jensen <k6...@foothill.net> > To: elecraft@mailman.qth.net > Subject: Re: [Elecraft] ARRL book on receiving antennas > Message-ID: <c130b735-6094-a565-3800-99fc2f9e2...@foothill.net> > Content-Type: text/plain; charset=utf-8; format=flowed > > Yes, very straightforward theory.? Just gather all the watts actually > radiated by the antenna and divide it by the watts you put into Rr.? > Unfortunately, I did not really address Bob's question ... "How do you > sweep up all those watts?" :-)? That is a nearly intractable problem at > HF unless you'll tolerate significant inaccuracies and assumptions.? > It's much easier at UHF and uWaves. > > An alternative is to measure/compute the losses.? Did something similar > on a 10 KW FM broadcast TX, calculating the power it took to heat the > exhaust air on the premise that the rest went up the coax to the antenna > and I knew what the PA input power was. > > KFBK in Sacramento CA [1530 KHz] eliminated a lot of the unmeasurable > variables by employing a Franklin antenna [center-fed half-wave > vertical] over the rice fields of the southern Sacramento Valley [nearly > always standing water, and always wet]. The center-fed vertical exhibits > far less ground losses than bottom-fed monopoles ... at 50 KW, it's > colloquially known as the "Flame Thrower of Sacramento."? It may be the > only Franklin left in NA.? KFBK is also famous as the birthplace of the > RCA Ampliphase transmitters and the radio birthplace of Rush Limbaugh. > > NEC models coupled with terrain models can be used to establish upper > and lower bounds on antenna efficiency with pretty good fidelity to > reality.? But Bob still posed a good question. > > 73, > > Fred ["Skip"] K6DGW > Sparks NV DM09dn > Washoe County > >> On 9/9/2018 2:01 PM, Don Wilhelm wrote: >> Skip, >> >> That is a great formula for theory - I vaguely remember it from my >> electromagnetic fields course. >> But how you measure it? >> With practical measurement equipment, it is difficult to isolate to a >> single plane. >> >> That may be do-able with fully characterized equipment in a controlled >> antenna field space or in an EMC lab, but it certainly is not >> practical in a typical ham antenna installation - and even the >> radiation resistance is not easily measured. >> >> Antenna modeling done properly will provide a much more easily >> produced result.? Comparative results between different antennas can >> be obtained from a reference pickup antenna, but that can only show >> the relative performance, > > > > ------------------------------ > > Message: 4 > Date: Sun, 9 Sep 2018 17:20:17 -0700 > From: Alan <n...@sonic.net> > To: elecraft@mailman.qth.net > Subject: Re: [Elecraft] ARRL book on receiving antennas > Message-ID: <96b660d3-5a7d-cb60-8d1d-827aaa6d7...@sonic.net> > Content-Type: text/plain; charset=utf-8; format=flowed > >> On 09/09/2018 01:01 PM, Jim Brown wrote: >>> On 9/9/2018 12:39 PM, Bob McGraw K4TAX wrote: >>> How does one measure transmit antenna efficiency? >> >> Not easily. :)? B... > >> AND -- propagation reporting systems like WSPR and the Reverse Beacon >> Network (RBN) can provide very good comparisons between antennas IF a >> LOT of reports from? a LOT of stations is averaged over a LOT of time. > > Back in the late 1970s, when I worked at W1AW, a new 90-foot tower with > stacked monobanders for 20 meters was installed. We wanted to compare > the new antenna against the big rhombic that had been used for many > years for the 20 meter bulletin and code practice transmissions. > > So, for a week or two, we did test transmissions after each scheduled > transmitting session. We would switch between antenna "A" and antenna > "B", send long dashes, and ask listeners to send in QSL reports. (Which > antenna was "A" and which was "B" varied randomly for each test.) > > I collected the reports and plotted them on a map of the US. We found > that the rhombic was a little better directly on its boresight to the > west (toward southern California from Connecticut) but the stacked Yagis > had a much wider beamwidth so were better over the country as a whole. > > By the way, you don't have to transmit to compare two antennas if your > receiver has an accurate S meter. Just switch between the antennas and > compare S meter readings. > > Alan N1AL > > > > ------------------------------ > > Message: 5 > Date: Sun, 9 Sep 2018 20:07:16 -0500 > From: Bob McGraw K4TAX <rmcg...@blomand.net> > To: elecraft@mailman.qth.net > Subject: Re: [Elecraft] ARRL book on receiving antennas > Message-ID: <ee36342c-268c-4e51-b52a-04a92586e...@blomand.net> > Content-Type: text/plain; charset=utf-8; format=flowed > > Thanks Fred.? I'm familiar with measuring broadcast fields for both > directional and non directional systems.? The variances over the seasons > with varying moisture levels in the ground and the difference with and > without vegetation is clearly measurable and predictable.? But still the > efficiency of the radiator was not clearly defined. > > As to hams, I suppose we individually evaluate a given antenna under the > conditions we have available.? From that we can say that given antenna > ZZ is more or less efficient than antenna XX.? What ever that XX antenna > happens to be.? While others may say that their XYZ is the best antenna > they have? ever had,? this may be true, that is until one may find > another antenna to be better. What ever "better" is defined.?? And > again, each of us will have objectives in terms of what our antenna and > station must attain.??? As Rob Sherwood said when asked "what is the > best receiver", his answer; "what ever satisfies your needs and you feel > as comfortable to operate and can afford". ? ? I suppose antennas are > much in the same vein of characterization. > > Yes, at VHF and UHF there are means and facilities to accurately measure > antenna efficiency.?? Usually we find those to be in the 60% to 80% > range.? Unfortunately some of the applied power is converted to heat, > the result of IR loss,? and thus is lost in terms of electromagnetic > radiation. ?? Again the means and the equipment required, as Jim K9YC > stated, generally is well above and beyond the means of most hams.???? > Some years ago I was fortunate to have supervised access to the antenna > test range at the Motorola facility in Florida and also at the anechoic > chamber owned by IBM in S. FL.?? These supported my graduate studies. > > No further answers required on my part.?? I've launched into a "reading" > project to further educate myself on the topic. > > > 73 > > Bob, K4TAX > > > > >> On 9/9/2018 5:48 PM, Fred Jensen wrote: >> Yes, very straightforward theory.? Just gather all the watts actually >> radiated by the antenna and divide it by the watts you put into Rr.? >> Unfortunately, I did not really address Bob's question ... "How do you >> sweep up all those watts?" :-)? That is a nearly intractable problem >> at HF unless you'll tolerate significant inaccuracies and >> assumptions.? It's much easier at UHF and uWaves. >> >> An alternative is to measure/compute the losses.? Did something >> similar on a 10 KW FM broadcast TX, calculating the power it took to >> heat the exhaust air on the premise that the rest went up the coax to >> the antenna and I knew what the PA input power was. >> >> KFBK in Sacramento CA [1530 KHz] eliminated a lot of the unmeasurable >> variables by employing a Franklin antenna [center-fed half-wave >> vertical] over the rice fields of the southern Sacramento Valley >> [nearly always standing water, and always wet]. The center-fed >> vertical exhibits far less ground losses than bottom-fed monopoles ... >> at 50 KW, it's colloquially known as the "Flame Thrower of >> Sacramento."? It may be the only Franklin left in NA.? KFBK is also >> famous as the birthplace of the RCA Ampliphase transmitters and the >> radio birthplace of Rush Limbaugh. >> >> NEC models coupled with terrain models can be used to establish upper >> and lower bounds on antenna efficiency with pretty good fidelity to >> reality.? But Bob still posed ______________________________________________________________ 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 c...@cfcorp.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
