[Elecraft] [OT] Magnetic Loops

[Julian, G4ILO]

Jim AB3CV wrote:
> 
>  According to the loop calculators available online at various sites the
> efficiency varies as a function of a number of parameters but making one
> for
> 20 or 30M at 90%+ efficiency is certainly possible. The efficiency will
> likely be limited by the number or type of joints in the assembly
> including
> those in the capacitor used for tuning.
> 
> One which would be likely suitable for 30M could be made out of aluminum
> flashing as demonstrated by NV7E (i don't think he did his for 30M). It
> uses
> the overlapped ends of the flashing to form the capacitor. If tuned to a
> QRP
> watering hole it would certainly work either side of the tuned location
> enough to allow QSO off the calling freq. This aluminum flashing version
> wouldn't likely withstand serious weather but might make a great antenna
> for
> the attic.
> 
> The higher the efficiency, the higher the Q but if you're rockbound, one
> frequency to get started while you're working on capacitor alternatives
> would seem to be a good start.
> 
> 

Here
http://carconline.blogspot.com/2009/01/coaxial-cable-40m-tunable-magnetic-loop.html
is a link to an interesting article about a magnetic loop made from coaxial
cable that uses the capacitance between the braid and the inner to tune it.
You vary the frequency by compressing or expanding the braid, securing it
with a wooden clothes peg. I love high technology!

I'm sure the number of joints in the assembly must make a measurable
difference but I'm not convinced that it would make one that is very
noticeable by ear. To anyone who is put off building a magnetic loop because
they don't think they can manage bending or soldering copper pipe or can't
get a split stator capacitor I'd say just get on and build one with what you
have. It'll work a lot better than miracle whips and other small portable
antennas and will cost a lot less to make than any of them also.

-----
Julian, G4ILO. K2 #392  K3 #222.
* G4ILO's Shack - http://www.g4ilo.com
* KComm - http://www.g4ilo.com/kcomm.html
* KTune - http://www.g4ilo.com/ktune.html

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