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.
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”.
Formerly with Group W Engineering, owner of both stations until recently.
>
>
> Message: 1
> Date: Sun, 9 Sep 2018 15:48:48 -0700
> From: Fred Jensen <
[hidden email]>
> To:
[hidden email]
> Subject: Re: [Elecraft] ARRL book on receiving antennas
> Message-ID: <
[hidden email]>
> 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 <
[hidden email]>
> To:
[hidden email]
> Subject: Re: [Elecraft] ARRL book on receiving antennas
> Message-ID: <
[hidden email]>
> 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 <
[hidden email]>
> To:
[hidden email]
> Subject: Re: [Elecraft] ARRL book on receiving antennas
> Message-ID: <
[hidden email]>
> 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