| |
KG6BAJ > NWSGRP 20.09.09 02:24l 36 Lines 1244 Bytes #999 (0) @ WW
BID : 11559_N1OES
Read: DL8DT GUEST
Subj: Resaonance and minimum SWR
Path: DB0FHN<DB0MRW<DB0ERF<OK0NHD<OK0PHL<OK0PCC<OM0PBC<OK0PPL<DB0RES<DK0WUE<
7M3TJZ<HG8LXL<CX2SA<KD4GCA<KG6BAJ<KG6BAJ
Sent: 090919/1200Z @:KG6BAJ.#NCA.CA.USA.NOAM #:11559 [Grass Valley] InterGate $
** NEWSGROUP: rec.radio.amateur.antenna
** FROM : "Antonio Vernucci" <vernucci@tin.it>
Reading here and there that the signals of the on-going DX-expedition to
Glorioso Island are generally very low, I got the curiosity to simulate the
so-called "spiderbeam" antenna they are using (sized for the 10-meter band) on
EZ-NEC.
Doing that, I obtained an unexpected result. The simulated antenna shows a clear
SWR minimum at 29.0 MHz where impedance is 76 + j32 ohm.
I then checked SWR across the 24 - 34 MHz range with the following results:
- going up in range 29 - 34 MHz, the reactance steadily increases (+334 ohm at
34 MHz)
- going down in range 29 - 24 MHz, the reactance remains positive and steadily
increases up to 28.5 MHz, after which it starts to decrease, until it becomes 0
ohm at 27 MHz, and negative below that frequency. At 27 MHz impedance is 9 + j0
ohm (hence it is the resonant point).
I knew that the resonant point does not precisely coincide with the minimum SWR
point, but I would not have suspected such a big difference (2 MHz shift at 29
MHz!).
Any comment?
Tony I0JX
Rome, Italy
From The KG6BAJ Newsgroup Server
** InterPacketGATE V1.6 Beta INTERNET <-> PACKET Radio Gateway by E.Konings **
Read previous mail | Read next mail
| |
