Correction, it was center fed. Sent from my iPad
> On Sep 11, 2018, at 19:23, Gmail <[email protected]> wrote: > > 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 <[email protected]> >> To: [email protected] >> Subject: Re: [Elecraft] ARRL book on receiving antennas >> Message-ID: <[email protected]> >> 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 <[email protected]> >> To: [email protected] >> Subject: Re: [Elecraft] ARRL book on receiving antennas >> Message-ID: <[email protected]> >> 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 <[email protected]> >> To: [email protected] >> Subject: Re: [Elecraft] ARRL book on receiving antennas >> Message-ID: <[email protected]> >> 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:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
