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Here's a link to the W8JI radiation resistance topic:
http://www.w8ji.com/radiation_resistance.htm where the antenna efficiency issue is analyzed - using a 1/4 long folded radiator as the example. In this analysis the antenna efficiency is unchanged because total power and ground loss power terms remain constant. Bob NW8L On Tue, 1 Oct 2013 14:48:55 -0700 "Ron D'Eau Claire" <[hidden email]> wrote: > The important value is the resistance at the feed point of the > radiator, independent of any matching devices used. > > Adding a 4:1 or other transformer is simply adjusting the impedance > the feed line sees, like any other matching network you might use. It > has no effect on the feed point resistance of the antenna. > > A 1/4 wave long folded radiator has a feed point resistance of 4x the > typical 1/4 wavelength radiator, quite independent of the ground > system. Hence the efficiency is higher. > > 73, Ron AC7AC > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by bill.va3ol
I had to calculate my radiation resistance to comply with the license
requirements on 600m. My antenna is a base loaded inverted-L: 43-feet high and 122-feet long*. Radiation resistance was taken from a EZ-NEC model as 0.83 ohms. Ground resistance was measured with an antenna analyzer as 18 ohms. efficiency = 0.83/18 = 0.046 Running transmitter output of 100w, Total Power Radiated = 100*0.046 = 4.6w EIRP = 4.6*1.48 = 6.8w anti-Log (1.7 dB) = 1.48, gain = 1.7 dB ERP = EIRP/1.64 = 4.15w which is the parameter wanted by the licensing authority. go to: http://www.kl7uw.com/600m.htm click on the EzNec model for the antenna analysis and ERP calculation for the rest. *Note the antenna was shortened from 130 to 122 feet to improve tension on the top-hat section. 73, Ed - KL7UW http://www.kl7uw.com [hidden email] "Kits made by KL7UW" ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by David Gilbert
I like to think of an Inverted L as a vertical antenna and a horizontal wire matching device. This is not entirely accurate, but is close enough for contact distances over 2000 miles. An examination of patterns with EZNEC will help you put this into perspective. The vertical portion is the difficult to erect portion of the inverted L and does most of the radiating for DX. The pattern is much like a short vertical for lower frequencies where the vertical length is usually much less than one quarter wave length, but the horizontal portion will raise the radiation resistance from usually single digits to nearer 50 ohms and increase the current in the vertical leg, thus give you more low angle signal. For higher frequencies where antenna vertical lengths greater than one quarter wave and radiation resistance more than 36 ohms or sometimes much less. An inverted L is often a good choice for 160 meters and sometimes 80 meters for those of us who
cannot erect a 250 foot vertical to get an optimum low angle signal. A 120 foot vertical is a good compromise and 15 or so ohms of ground resistance is a good counterpoise for a near 50 ohm match, but if that is not doable a 60 foot vertical and a 60 or so foot horizontal leg is a decent antenna with a more reasonable cost. If your operating frequency is higher then the inverted L is attractive only under special circumstances such as emergency, portable or antenna restrictions. Willis 'Cookie' Cooke K5EWJ & Trustee N5BPS, USS Cavalla, USS Stewart ________________________________ From: David Gilbert <[hidden email]> To: [hidden email] Sent: Tuesday, October 1, 2013 5:09 PM Subject: Re: [Elecraft] Random wires I suggest reading W8JI ... and others. http://www.w8ji.com/radiation_resistance.htm Dave AB7E On 10/1/2013 2:53 PM, [hidden email] wrote: > Sorry roger, Roger, your analysis is not totally correct. You do raise the feed impedence from 36 Ohms as compared to using a single 1/4 wave wire over perfect ground. As most of us do not have perfect ground, there is an imperfect representation of the virtual 1/4. Because it is imperfect, you can look at this part as absorbing energy and just returning heat. By raising the radiation impedance, less energy is absorbed by ground and more is radiated. How much additional efficiency do you obtain is a matter of the ground system you put in and the ground constants under it. In my experience, it is worth the effort to build the antenna as it will outperform a similar single wire inverted L. I suggest reading Bill Orr, and others, on this antenna. > > 73, > Barry > K3NDM > > ----- Original Message ----- > > From: "Roger D Johnson" <[hidden email]> > To: [hidden email] > Sent: Tuesday, October 1, 2013 3:40:49 PM > Subject: Re: [Elecraft] Random wires > > This is NOT true! It merely raises the feedpoint impedance...just the same as > adding a > 4-1 transformer. > > 73, Roger > > > On 10/1/2013 3:10 PM, Barry LaZar wrote: >> >> As I read your post, I infer that at the moment you are wanting to add 160 >> meters to your capability. An antenna that I have used and liked is the Twin >> Lead Marconi. It's a simple, cheap, and effective antenna. I first saw it >> written up by Bill Orr years ago. The premise of the design is that a quarter >> wave antenna driven against ground may not be the most efficient antenna due >> to low radiation resistance. Therefore, raise the radiation resistance by >> using the theory of a folded dipole. The folded element raises the radiation >> resistance by a factor of 4 for 2 elements as the impedance changes as the >> square of the number of elements. You will still need radials, but your ground >> losses will decrease. >> >> >> 73, >> Barry >> K3NDM >> >> ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Edward R Cole
You're slightly more QRP than you think. Efficiency is radiation resistance divided by total resistance (not ground resistance). So your calculation should be:
efficiency = 0.83/(18+0.83) = 0.044 Running transmitter output of 100w, Total Power Radiated = 100*0.044 = 4.4w EIRP = 4.4*1.48 = 6.5w anti-Log (1.7 dB) = 1.48, gain = 1.7 dB ERP = EIRP/1.64 = 3.98w John, KU4AF Pittsboro, NC <quote author="Edward R Cole"> My antenna is a base loaded inverted-L: 43-feet high and 122-feet long*. Radiation resistance was taken from a EZ-NEC model as 0.83 ohms. Ground resistance was measured with an antenna analyzer as 18 ohms. efficiency = 0.83/18 = 0.046 Running transmitter output of 100w, Total Power Radiated = 100*0.046 = 4.6w EIRP = 4.6*1.48 = 6.8w anti-Log (1.7 dB) = 1.48, gain = 1.7 dB ERP = EIRP/1.64 = 4.15w which is the parameter wanted by the licensing authority. |
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In reply to this post by Robert Cunnings
Everybody,
I see a real problem here. Please someone open up the authority, Krause, and see what he says. His work is the basis of a whole lot of what we have today. 73, Barry K3NDM On 10/1/2013 10:55 PM, Bob Cunnings wrote: > Here's a link to the W8JI radiation resistance topic: > > http://www.w8ji.com/radiation_resistance.htm > > where the antenna efficiency issue is analyzed - using a 1/4 long > folded radiator as the example. In this analysis the antenna efficiency > is unchanged because total power and ground loss power terms remain > constant. > > Bob NW8L > > On Tue, 1 Oct 2013 14:48:55 -0700 > "Ron D'Eau Claire" <[hidden email]> wrote: > >> The important value is the resistance at the feed point of the >> radiator, independent of any matching devices used. >> >> Adding a 4:1 or other transformer is simply adjusting the impedance >> the feed line sees, like any other matching network you might use. It >> has no effect on the feed point resistance of the antenna. >> >> A 1/4 wave long folded radiator has a feed point resistance of 4x the >> typical 1/4 wavelength radiator, quite independent of the ground >> system. Hence the efficiency is higher. >> >> 73, Ron AC7AC >> > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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What do you expect Krause will tell you? That feedpoint impedance and radiation resistance are the same thing?? I guarantee that it will not. Did you not understand that feedpoint transformations transform the combination of all impedances present at that point, and therefore leave the relative magnitude of the various components (and therefore the efficiency of the system) the same?? Or are you somehow of the opinion that a folded element is not a feedpoint transformation?? I'm really having trouble understanding your logic here. Dave AB7E On 10/2/2013 9:26 AM, Barry LaZar wrote: > Everybody, > I see a real problem here. Please someone open up the authority, > Krause, and see what he says. His work is the basis of a whole lot of > what we have today. > > 73, > Barry > K3NDM > > > On 10/1/2013 10:55 PM, Bob Cunnings wrote: >> Here's a link to the W8JI radiation resistance topic: >> >> http://www.w8ji.com/radiation_resistance.htm >> >> where the antenna efficiency issue is analyzed - using a 1/4 long >> folded radiator as the example. In this analysis the antenna efficiency >> is unchanged because total power and ground loss power terms remain >> constant. >> >> Bob NW8L >> >> On Tue, 1 Oct 2013 14:48:55 -0700 >> "Ron D'Eau Claire" <[hidden email]> wrote: >> >>> The important value is the resistance at the feed point of the >>> radiator, independent of any matching devices used. >>> >>> Adding a 4:1 or other transformer is simply adjusting the impedance >>> the feed line sees, like any other matching network you might use. It >>> has no effect on the feed point resistance of the antenna. >>> >>> A 1/4 wave long folded radiator has a feed point resistance of 4x the >>> typical 1/4 wavelength radiator, quite independent of the ground >>> system. Hence the efficiency is higher. >>> >>> 73, Ron AC7AC >>> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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No. I expected someone who is an engineer and commands the language
better than I to explain that they are not the same and how they fit together thereby adding a little enlightenment to this thread. 73, Barry K3NDM On 10/2/2013 1:07 PM, David Gilbert wrote: > > What do you expect Krause will tell you? That feedpoint impedance and > radiation resistance are the same thing?? I guarantee that it will not. > > Did you not understand that feedpoint transformations transform the > combination of all impedances present at that point, and therefore > leave the relative magnitude of the various components (and therefore > the efficiency of the system) the same?? Or are you somehow of the > opinion that a folded element is not a feedpoint transformation?? > I'm really having trouble understanding your logic here. > > Dave AB7E > > > > On 10/2/2013 9:26 AM, Barry LaZar wrote: >> Everybody, >> I see a real problem here. Please someone open up the authority, >> Krause, and see what he says. His work is the basis of a whole lot of >> what we have today. >> >> 73, >> Barry >> K3NDM >> >> >> On 10/1/2013 10:55 PM, Bob Cunnings wrote: >>> Here's a link to the W8JI radiation resistance topic: >>> >>> http://www.w8ji.com/radiation_resistance.htm >>> >>> where the antenna efficiency issue is analyzed - using a 1/4 long >>> folded radiator as the example. In this analysis the antenna efficiency >>> is unchanged because total power and ground loss power terms remain >>> constant. >>> >>> Bob NW8L >>> >>> On Tue, 1 Oct 2013 14:48:55 -0700 >>> "Ron D'Eau Claire" <[hidden email]> wrote: >>> >>>> The important value is the resistance at the feed point of the >>>> radiator, independent of any matching devices used. >>>> >>>> Adding a 4:1 or other transformer is simply adjusting the impedance >>>> the feed line sees, like any other matching network you might use. It >>>> has no effect on the feed point resistance of the antenna. >>>> >>>> A 1/4 wave long folded radiator has a feed point resistance of 4x the >>>> typical 1/4 wavelength radiator, quite independent of the ground >>>> system. Hence the efficiency is higher. >>>> >>>> 73, Ron AC7AC >>>> >>> ______________________________________________________________ >>> Elecraft mailing list >>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>> Help: http://mailman.qth.net/mmfaq.htm >>> Post: mailto:[hidden email] >>> >>> This list hosted by: http://www.qsl.net >>> Please help support this email list: http://www.qsl.net/donate.html >>> >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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This comment made me do a search on Kraus.
I found one of his books online for free in the open source archive.org site (this is the streaming link, they also have it in PDF):http://archive.org/stream/Antennas2ndbyjohnD.Kraus1988/Kraus-Antennas-2nd.Edition-1988#page/n0/mode/2up I though others might like to look at it. 73 - Tom - wa4ta > Date: Wed, 2 Oct 2013 13:36:36 -0400 > From: [hidden email] > To: [hidden email] > Subject: Re: [Elecraft] Random wires > > No. I expected someone who is an engineer and commands the language > better than I to explain that they are not the same and how they fit > together thereby adding a little enlightenment to this thread. > > 73, > Barry > K3NDM > > On 10/2/2013 1:07 PM, David Gilbert wrote: > > > > What do you expect Krause will tell you? That feedpoint impedance and > > radiation resistance are the same thing?? I guarantee that it will not. > > > > Did you not understand that feedpoint transformations transform the > > combination of all impedances present at that point, and therefore > > leave the relative magnitude of the various components (and therefore > > the efficiency of the system) the same?? Or are you somehow of the > > opinion that a folded element is not a feedpoint transformation?? > > I'm really having trouble understanding your logic here. > > > > Dave AB7E > > > > > > > > On 10/2/2013 9:26 AM, Barry LaZar wrote: > >> Everybody, > >> I see a real problem here. Please someone open up the authority, > >> Krause, and see what he says. His work is the basis of a whole lot of > >> what we have today. > >> > >> 73, > >> Barry > >> K3NDM > >> > >> > >> On 10/1/2013 10:55 PM, Bob Cunnings wrote: > >>> Here's a link to the W8JI radiation resistance topic: > >>> > >>> http://www.w8ji.com/radiation_resistance.htm > >>> > >>> where the antenna efficiency issue is analyzed - using a 1/4 long > >>> folded radiator as the example. In this analysis the antenna efficiency > >>> is unchanged because total power and ground loss power terms remain > >>> constant. > >>> > >>> Bob NW8L > >>> > >>> On Tue, 1 Oct 2013 14:48:55 -0700 > >>> "Ron D'Eau Claire" <[hidden email]> wrote: > >>> > >>>> The important value is the resistance at the feed point of the > >>>> radiator, independent of any matching devices used. > >>>> > >>>> Adding a 4:1 or other transformer is simply adjusting the impedance > >>>> the feed line sees, like any other matching network you might use. It > >>>> has no effect on the feed point resistance of the antenna. > >>>> > >>>> A 1/4 wave long folded radiator has a feed point resistance of 4x the > >>>> typical 1/4 wavelength radiator, quite independent of the ground > >>>> system. Hence the efficiency is higher. > >>>> > >>>> 73, Ron AC7AC > >>>> > >>> ______________________________________________________________ > >>> Elecraft mailing list > >>> Home: http://mailman.qth.net/mailman/listinfo/elecraft > >>> Help: http://mailman.qth.net/mmfaq.htm > >>> Post: mailto:[hidden email] > >>> > >>> This list hosted by: http://www.qsl.net > >>> Please help support this email list: http://www.qsl.net/donate.html > >>> > >> > >> ______________________________________________________________ > >> Elecraft mailing list > >> Home: http://mailman.qth.net/mailman/listinfo/elecraft > >> Help: http://mailman.qth.net/mmfaq.htm > >> Post: mailto:[hidden email] > >> > >> This list hosted by: http://www.qsl.net > >> Please help support this email list: http://www.qsl.net/donate.html > >> > > > > ______________________________________________________________ > > Elecraft mailing list > > Home: http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/mmfaq.htm > > Post: mailto:[hidden email] > > > > This list hosted by: http://www.qsl.net > > Please help support this email list: http://www.qsl.net/donate.html > > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by bill.va3ol
John,
Thankyou for the correction in the formula. In fact the 18-ohms measured by the antenna analyzer is the total resistance and includes both radiation resistance and ground resistance, so my numbers are correct, just not my explanation of them. This was done three years ago and I forgot some of it. Like others have observed not something calculated everyday. Direct measurement of radiation resistance is the difficult part, so this provides the required calculation with the normal uncertainty of antenna modeling. One can understand the problem of installing a quarter-wave vertical on 500-KHz which would be 415 foot tall. I do not have the resources for really tall antenna (even 200-foot would be nice), so the top loading of the inverted-L is one of the standard antenna for low-low bands. Then one considers quarter-wave radials - you need some real estate! Yet even with this obvious compromise my signal has been detected 2800 miles running only 4.15w ERP. The new ham band will likely only permit 1w to 5w ERP so this is in the ball-park of what is possible. 73, Ed - KL7UW, WD2XSH/45 ----------------- From: KU4AF <[hidden email]> To: [hidden email] Subject: Re: [Elecraft] Random wires Message-ID: <[hidden email]> Content-Type: text/plain; charset=us-ascii You're slightly more QRP than you think. Efficiency is radiation resistance divided by total resistance (not ground resistance). So your calculation should be: 73, Ed - KL7UW http://www.kl7uw.com [hidden email] "Kits made by KL7UW" ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Barry K3NDM
On 10/2/2013 10:36 AM, Barry LaZar wrote:
> No. I expected someone who is an engineer and commands the language > better than I to explain that they are not the same and how they fit > together thereby adding a little enlightenment to this thread. Since this is the Elecraft reflector, the discussion has wandered pretty far off topic. Dave, Willis, Ed, and I have jumped in to correct some serious misconceptions, but that's about as far as I'm prepared to stretch our welcome. :) 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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