http://elecraft.85.s1.nabble.com/Efficiency-of-MFJ-remotely-tuned-loop-antennas-tp7667578p7667598.html
Thank you for sharing that... I have saved it to my system.
ARRL Asst. Director, NW Division, Technical Resources
> MFJ makes a pair of small, remotely-tuned loop antennas, the MFJ-1786
> that covers 10-30 MHz and the MFJ-1788 that covers 7 to 21+ MHz. As far
> as I can tell, the two antennas are identical except for the size of the
> tuning capacitor. Each consists of a 3 foot (91 cm) diameter loop made
> of aluminum tubing and a plastic housing that contains the tuning
> capacitor, motor, and coupling loop. No control cable is required since
> the control voltage is sent from the control box in the shack to the
> motor in the antenna via the coaxial cable.
>
> Before I purchase one of these I wanted to get an idea of the efficiency
> of such a small loop. MFJ is silent on the subject so I did my own
> calculations. The calculations and results are on a 1-page document
> that I uploaded to Dropbox and can be downloaded here:
>
>
https://www.dropbox.com/s/l8mv67cjrck2ssn/MFJ-1786-1788.pdf?dl=0>
> My calculations are based on the assumption that the efficiency of the
> MFJ antennas is similar to the (no longer manufactured) AEA Isoloop (my
> reasoning for that is in the document) and that AEA's specification of
> 72% efficiency at 14 MHz is correct. From that number I can calculate
> the efficiency and gain on all the other bands.
>
> If you don't want to download the document, here is a summary of the
> results:
>
> Freq Eff Gain with respect to a half-wave dipole
> MHz dB dBd
> 7.0 -7.3 -7.7
> 10.1 -3.5 -3.9
> 14.0 -1.4 -1.8
> 18.068 -0.6 -1.0
> 21.0 -0.4 -0.8
> 24.89 -0.2 -0.6
> 28.0 -0.15 -0.5
>
> I'd be interested in any comments people may have on the accuracy of
> my assumptions and calculations in the document.
>
> Alan N1AL
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