[Elecraft] dipole antenna efficiency

[Shaun Oliver]

bloody 'ell,,, that was slightly more than I barganned for. oh well, 
every little bit helps, and ultimately confuses.
shaun.


On 4/01/2008 11:58 PM, the old scribe known as Dale Putnam was able to 
impart this pearl of wisdom:
> What is needed is a good effecient, multiband antenna with a general 
> coverage pattern.
> The old saying applies... higher is better. Ok.. now that means up is 
> good. Low isn't. Unless you are
> intent upon working everyone, including the local tv, stereo, and 
> sometimes even the  garage door opener, within a couple hundred miles. 
> So.. high is good.
>   Now.. lets take a little bite at a time. A finite amount of power out 
> of a transmitter.. that doesn't change much, or shouldn't at least. So.. 
> power out.. now it radiates best from an antenna... ok... now, it seems 
> to me that the best way to get the power to the antenna is with a 
> feedline, and the more power that can get into the antenna, the better 
> it will get radiated. So.. best feedline, under the conditions... 
> installation restrictions apply. The best feedline in the world... won't 
> do a lotta good if it isn't installed correctly. Shorts.. poor 
> connectors... bends too tight,... too close to metal... all apply.
> How about asking the feedline to transfer power outside of the 
> parameters that it was intended? Ok.. so what is best? We ask feedline 
> to transfer power over a range of freq. into an antenna that is asked to 
> radiate with high effectiveness over the same range. If you want to do 
> the math... go for it. There are others that do that rather well... I'd 
> drather spend time playing radio, but the math still applies. So.. what 
> works? Everyone has their own "best". Generally speaking, the most 
> effective is a rather high impedance transmission or feedline. Ok... 
> open line.. window line.. homebrew... high price...  all are 
> considerations.. even consideration of a single wire feeder known as a 
> "G" transmission line will do rather well, if the previous 
> considerations are taken. So.. now we have a feedline. Next the antenna. 
> Oh boy, here it comes,  to where the rope meets leather. The antenna 
> needs to radiate. Really well.. and that is generally measured at the 
> other fellow's s meter or ears. Ok, so first, where do you want to talk? 
> Lets break it down. Inside a 600 mile radius or outside that circle? Now 
> we all want to talk all over the world... and have the strongest signal 
> all the time.. That just isn't going to happen. If a good signal is to 
> be expected within the country.. the antenna needs to be able to radiate 
> in such a manner as to put a signal to right  "there"! Ok, we can all 
> figure out which antenna has what radiation pattern.... on paper.
> And that is a great start. Now... how about the ground effects... the 
> extra bends and twists? All those can be considered, sure, but the 
> overriding thought may well be that the antenna needs to accept the 
> power being brought to it, and radiate it. Resonance, or being "cut to 
> frequency" works well for the imedance match to the feedline, if that is 
> a choice to apply. If it is a low impedance feedline.. a small change 
> will be noticed, because a  5 ohm change referenced to 50, isn't the 
> same as the same 5 ohm difference referenced to 600 ohm.  Bottom line? 
> Ok.. here it is.. an antenna that works over the range that is needed, 
> and radiates with the best chosen pattern, with the highest transfer of 
> power from the feedline to the ether. Pick one... there are many. Many, 
> many pages of very good information is available to help you choose. 
> That is applicable.. right now. With the winter weather upon us.. now is 
> the time for a bit of reading, consideration... and choose. And.. if you 
> really want that antenna to stay up?... better consider putting it up in 
> the winter too.. if you put it up in the winter, it will last longer.. 
> and pretty much work well. Some of the best antennas I've used, have 
> been put up in the dead of winter, and some during blizzards. Not 
> necessarily recommended. Which would you rather do? Build it, or maybe 
> read about it and choose wisely, get everything ready.. and the first 
> warm day... get ready... get set... then build away!
>  
> See you in the pileups, foxhunts, and most importantly... in the log, 
> and that's a nice QSL too!
> 
> --... ...--
> Dale - WC7S in Wy
> 
> 
> 
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