Re: Design for small tunable loop?

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From: Rick Zabrodski (zabrodsk@med.ucalgary.ca)
Date: Sun Jun 18 1995 - 10:32:53 EDT


Quote from chapter 3 of "Small High Effieciency Antennas" by W5QJR:
"A loop will provide high efficiency when made of 3/4 inch copper pipe
and having a circumference of more than 1/8 wavelength and less than 1/3
wavelength."

Actually, bigger diameter tubing better for lower HF frequencies.
If it is physically bigger than 1/3 of a wavelenght the pattern and other
characteristics change and there is no improvement in efficiency.
Below 1/8 wavelength the effeciency really drops! (as does bandwidth)

I played with one of these a few years ago, before the commericial
products were around and before there was any stuff in the ARRL handbook.
Good connections essential! Making a capacitor was a real pain.....I
lucked into a "brand new in the box" vacum tube variable which was great.

Performance: yes it worked, yes it was quiet. My wire dipole and loop
antennas were better performers. Fun project but simpler antennas that
are cheaper can be homebrewed! The real advantage of this concept would
be to make a "small" city lot antenna for 160m that was quiet. (Even typical
dipoles etc on 160 are very low to the ground at this wavelength.
Note: "Small" for 160m would be 66 to 150 feet in circumference and at
least a 3" diameter conductor!!!!!!

Dr. Rick Zabrodski BSc, MD, CCFP(E) * VE6GK
Email: zabrodsk@med.ucalgary.ca * NorCal 519 ARCI 7650 GQRP 8329
Phone 403-271-5123 Fax 403-225-1276 * "Power is no substitute for skill"
                                                                

On Sat, 17 Jun 1995 JCoote@aol.com wrote:

> There is some stuff by W5QJR on loops in one of the ARRL antenna compendiums.
> His designs are small, thick-diameter, current loops similar to the MFJ
> loop. For 7-30 Mhz you may be talking about a loop diameter of 5-6 feet...
> if you look at the MFJ and AEA loops which are 10-30 Mhz and about 3 feet.
>
> 72, Jay
>
>


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