[AMPS] Finding the Q of a Coil

[2]

>
>> >Accurate calculation of RF resistance definitely is the tough part. 
>> >There is more than one set of formulas from different sources for
>> >calculating this and the results don't agree. If I were forced to
>> >choose, I'd probably stick with the formulae in Terman's books.  
>> >Steve T. correctly outlined the general procedure.  I too will have a
>> >look at the Murphy file that Ian suggested.
>> >
>> I should have mentioned, it's all based on info from Terman.
>
>This is one of the cases I have found where you had just better 
>measure the component.
>
//   I have seen too many VHF antennas where the calculated gain was 
different than the measured gain.  It is no wonder that *QST* does not 
allow antenna manufacturers to make gain claims.  In CB rags, one finds 
gain claims of 11+db for 3-element yagis.

>It seems is difficult if not virtually impossible to get close to actual 
>component Q using formulas. Many things are at issue besides 
>wire resistance. Every Q formula working off coil dimensions or 
>program I have tried has never been close.
>
>The work by Czerwinski in August 26 1960 Electronics comes 
>closest, while some of Terman's stuff is miles from being correct.

//  Terman's inductance formula predicts that the L of 1-inch/25mm width 
copper strap is about 10nH per inch.  However, in the Rauchian world, an 
inch of such strap has zero inductance -- especially when it is used to 
ground a grid.  
>
cheers

-  R. L. Measures, 805.386.3734, AG6K, www.vcnet.com/measures.  
end


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