Wednesday, February 23, 2011

Notes on a 20-15M small transmitting loop

From slogging through the loop calculations and formulas I think it would be possible to build a loop to cover 15M, 17M & 20M. It would be 3.3 Ft in diameter ... more than a foot smaller across than my 40M double loop. The efficiency looked like it was going to drop a fair bit from 15M to 20M but then I realized that loss would represent much less than 1 S unit. The calculations were based on a 11 Ft circumference of 3/4 in copper pipe.

Frequency Capacitance Required Ham Band Efficiency
21 Mhz 24 pF 15M 89% - 0.5dB below 100%
18 Mhz 33 pF 17M 83% - 0.8dB below 100%
14 Mhz 55 pF 20M 66% - 1.8dB below 100%

In theory it would be possible to operate the loop down at 40M with a large enough capacitance but with greatly reduced efficiency ... perhaps a few S units down (8.3 dB below 100%) ... you could push 50W and still fair ok with PSK31 and Olivia in a pinch.
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