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Checking the loop calculations using a formula from (C)
The
use, publication, copy and modification of all info on this site is only
permitted for purposes, and thereby non-commercialexplicitly
mentioning my radio amateur call sign "PA0NHC", as the original
writer / designer / photographer /publisher. (C) |

At the tuning capacitor, G0CWT on 7.1 MHz 22.2 Ohms. on 3.65MHz 2.4 Ohms. |

According to **DL4KCJ, **the **loaded Q** of a loop antenna

The loaded Q of a loop only using the formula : Ql = Xc / Zloadcan be accurately calculated |

**7.1 MHz : Ql = Xc(63pF) / Zl(7MHz) = 356 / 22.2 = 16.
3.65 MHz : Ql = Xc(240pF) / ZL(3.5MHz)= 182 / 2.4 = 76.**

** The voltage over the tuning capacitor at 100W power now is :**

**Urms = (SQRT(P x Zl)) x Ql.
7.1 MHz : (SQRT(100 x 22.2)) x 16 = 754 Vrms => 1063 Vp.
3.65 MHz : (SQRT(100 x 2.4)) x 76 = 1177 Vrms => 1660 Vp.
**

THIS PAGE GIVES NO CORRECT CALCULATIONS FOR 1/4 WAVE CIRCUMFERENCE LOOPS. |

**Check :**

**7MHz: I = SQRT(P / Zl) = SQRT(100 / 22.2) = 2.12 A (flowing through the tuning capacitor).
Uc = I x Xc = 2.12 x 556 = 756Vrms => 1065 Vp. (not 4kVp).**

**3.65 MHz : I = SQRT(100 / 2.4) = 6.45 A
Uc = 6.45 x 182 = 1174 Vrms => 1655 Vp. (not 4kVp!).**

Using 100W, a plate distance of 2mm is sufficient. Using 800W on 7,1 MHz, the capacitor voltage will be abt. 3kVp

Tested in humid weather, open cabinet, with 100W power NO arcing was noticed.

The 5W heather prevents condensation in a closed cabinet.