3152	2009-06-06 12:30:14	Stan	Inductors as components of dipole elements questions
Message	Date	From	Subject
I have a technical question about the use of inductors as a component of an antenna element. It is a given that short dipoles are less effective than longer dipole especially the longer ones which are resonant. However, several commercial beams have been quite successful over the years which were considerable shorter than standard and it was accomplished by the use of inductors. In addition, we all know mobiles with extremely short vertical whips do very well in working all over the country. Does anyone know how to calculate the efficiency of a shorten dipole element in regards to a full size dipole element? Do we lose 30 percent or 50 percent or is it less than 10%? What are the real numbers and how can we come up with them? For Example I have been looking at the Shorty 40 meter dipole. It uses two inductors at the center of the antenna to take the place of length of dipole element. It also uses an inductor as a hairpin match. What would be the efficiency of such an antenna when compared to a full size 40 meter dipole? All other factors height, etc. being the same for both antenna. Lets assume the efficiency is not as bad as expected. Would the efficiency be improved if the inductors were moved from the center of the antenna toward the ends? It appears with short whips the efficiency improves as the inductor is moved toward the top. If this is true since short (small) capacity hats improved the efficiency of a short whip would not the same be true of a short dipole? I apologize, I know this is not an antenna list. However, I do believe it is considerable more technical than the average email list on the web. And we are talking about how components (inductors) help or hinder the performance of a dipole element which may be OT but not much. Thanks for the bandwidth. Stan AK0B
3154	2009-06-06 16:50:32	Dave Brainerd	Re: Inductors as components of dipole elements questions
Stan wrote: > I have a technical question about the use of inductors as a component of an antenna element. It is a given that short dipoles are less effective than longer dipole especially the longer ones which are resonant. > > However, several commercial beams have been quite successful over the years which were considerable shorter than standard and it was accomplished by the use of inductors. > > In addition, we all know mobiles with extremely short vertical whips do very well in working all over the country. > Does anyone know how to calculate the efficiency of a shorten dipole element in regards to a full size dipole element? Do we lose 30 percent or 50 percent or is it less than 10%? What are the real numbers and how can we come up with them? > > For Example I have been looking at the Shorty 40 meter dipole. It uses two inductors at the center of the antenna to take the place of length of dipole element. It also uses an inductor as a hairpin match. What would be the efficiency of such an antenna when compared to a full size 40 meter dipole? All other factors – height, etc. being the same for both antenna. > > Lets assume the efficiency is not as bad as expected. Would the efficiency be improved if the inductors were moved from the center of the antenna toward the ends? It appears with short whips the efficiency improves as the inductor is moved toward the top. If this is true since short (small) capacity hats improved the efficiency of a short whip would not the same be true of a short dipole? > > I apologize, I know this is not an antenna list. However, I do believe it is considerable more technical than the average email list on the web. And we are talking about how components (inductors) help or hinder the performance of a dipole element which may be OT but not much. Thanks for the bandwidth. > > Stan AK0B > > > > > I don't really know how to calculate the loss. But, moving the coil from the center torwards the top of a whip improves the efficiency because less current is flowing through it creating less loss. Also, use of a capacity top hat improves efficiency. Bigger wire in the coil reduces the I2R losses in the coil. Larger diameter pipe or wire for the antenna widens the bandwidth. Dave - WB6DHW <http://wb6dhw.com>
3155	2009-06-06 17:45:09	Sam Morgan	Re: Inductors as components of dipole elements questions
Stan wrote: > I have a technical question about the use of inductors as a component of > an antenna element. It is a given that short dipoles are less effective > than longer dipole especially the longer ones which are resonant. > snip check out: http://www.zerobeat.net/G4FGQ/page3.html#S301%22 perhaps 'midload' would answer some of your questions there may be others for dipoles in the list, there are also many for verticals, I'll let you browse and discover Good luck and enjoy -- GB & 73 KA5OAI Sam Morgan
3156	2009-06-06 20:18:10	Russell Shaw	Re: Inductors as components of dipole elements questions
Stan wrote: > I have a technical question about the use of inductors as a component of an antenna element. It is a given that short dipoles are less effective than longer dipole especially the longer ones which are resonant. > > However, several commercial beams have been quite successful over the years which were considerable shorter than standard and it was accomplished by the use of inductors. > > In addition, we all know mobiles with extremely short vertical whips do very well in working all over the country. > Does anyone know how to calculate the efficiency of a shorten dipole element in regards to a full size dipole element? Do we lose 30 percent or 50 percent or is it less than 10%? What are the real numbers and how can we come up with them? > > For Example I have been looking at the Shorty 40 meter dipole. It uses two inductors at the center of the antenna to take the place of length of dipole element. It also uses an inductor as a hairpin match. What would be the efficiency of such an antenna when compared to a full size 40 meter dipole? All other factors – height, etc. being the same for both antenna. > > Lets assume the efficiency is not as bad as expected. Would the efficiency be improved if the inductors were moved from the center of the antenna toward the ends? It appears with short whips the efficiency improves as the inductor is moved toward the top. If this is true since short (small) capacity hats improved the efficiency of a short whip would not the same be true of a short dipole? > > I apologize, I know this is not an antenna list. However, I do believe it is considerable more technical than the average email list on the web. And we are talking about how components (inductors) help or hinder the performance of a dipole element which may be OT but not much. Thanks for the bandwidth. Calculate the radiation resistance: http://en.wikipedia.org/wiki/Radiation_resistance and the skin effect resistance of the antenna and coils: http://en.wikipedia.org/wiki/Skin_effect Efficiency is then Pradiated/(Pradiated + Pskineffect + Pcoil) P = i^2.R Pcoil = Icoil^2.Rcoil Current varies along the wire as a triangular distribution for short dipole antennae, so Icoil can be approximately determined depending on where the coil(s) is positioned, and knowing the total power. The efficiency can be from near 0% to near 100%. Proximity of other objects and the ground also reduces efficiency. A complete formula could be devised, but that would be a bit more effort.