G8MNY > TECH 18.06.25 08:45z 107 Lines 4153 Bytes #188 (0) @ WW BID : 34999_GB7CIP Subj: Actual Antenna SWR Path: ED1ZAC<ED1ZAC<GB7CIP Sent: 250618/0836Z @:GB7CIP.#32.GBR.EURO #:34999 [Caterham Surrey GBR] From: G8MNY@GB7CIP.#32.GBR.EURO To : TECH@WW From Peter LZ1LEN (8 Bit ASCII graphics use code page 437 or 850, Terminal Font) Below is one little, easy for calculate formula with two tables, which could be a wake-up call for you. Don't over-trust the goodlooking indication of your precious SWR-meter, which is situated at your worktable. Because the SWR value at the input of antenna cable is not a actual SWR of your favorite "WONDER-antenna". Description: ------------ You can calculate it yourself what is "the simple truth" with following simplified formula: b + c SWRa = ------- b - c where: SWRa = actual SWR at antenna input (cable far end) b = coefficient vs.actual cable attenuation in dB c = coefficient vs.checked SWR (SWRc) @ cable input(measuring point) Ó ÚÄÄÄÄÄ¿ ÚÄÄÄÄÄ¿ Ú Cable with well-known(in dBs)Loss Ó ³ TRX oÄÄÄÄo SWR oÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄoÄÄÓ Antenna ÀÄÄÄÄÄÙ ÀÄÄÄÄÄÙ\ checked SWRc / Ó actual SWRa / Ó Table #1 -------- Values of "b" vs. actual cable attenuation in dB: Remark: At right side are shown approx. Cable Length for 2 typical cables @ 145MHz ---------------------------------------- | dBs | b | RG-213/U | RG-58/U | ---------------------------------------- 0.0 1.0 0.0 m 0.0 m 0.5 0.8912 6.25 m 2.12 m 1.0 0.7943 12.5 m 4.25 m 1.5 0.7079 18.75 m 6.38 m 2.0 0.6309 25.0 m 8.5 m 2.5 0.5623 31.25 m 10.64 m 3.0 0.501 37.5 m 12.76 m 3.5 0.4466 43.75 m 14.89 m 4.0 0.3981 50.0 m 17.02 m 5.0 0.3162 62.5 m 21.2 m 6.0 0.2511 75.0 m 25.53 m 7.0 0.1995 87.5 m 29.78 m 8.0 0.1584 100.0 m 34.04 m 9.0 0.1258 112.5 m 38.3 m 10.0 0.1 125.0 m 42.55 m 11.0 0.0794 137.5 m 46.8 m 12.0 0.063 150.0 m 51.0 m ---------------------------------------- Table #2 -------- Values of "c" vs. checked SWR @ cable input (measuring point) ---------------------------------------- | SWRc | c | | SWRc | c | ---------------------------------------- | 1.0 0 | | 1.8 0.2857 | | 1.1 0.0476 | | 1.9 0.3103 | | 1.2 0.0909 | | 2.0 0.3333 | | 1.3 0.1304 | | 2.5 0.4285 | | 1.4 0.1666 | | 3.0 0.5 | | 1.5 0.2 | | 4.0 0.6 | | 1.6 0.2307 | | 5.0 0.6666 | | 1.7 0.2592 | | 10.0 0.8181 | ---------------------------------------- Notes: ------ * The cable attenuation in dB & SWR at antenna are actual values vs. actual frequency & all others (bad)influenced factors. ** For determinating of the antenna cable attenuation, you can use both programms "Antenna Cable Loss & SWR" or "Antenna Cable Loss & SWR Calculator" on the address: http://www.qsl.net/lz1len/projects.html Examples: --------- 1+0 1) dBs=0dB (b=1); SWRc=1 (c=0); SWRa= ----- = 1 (Border case, the Dream) 1-0 0.5623+0.2 0.7623 2) dBs=2.5dB (b=0.5623); SWRc=1.5 (c=0.2); SWRa= ---------- = ------ = 2.1 0.5623-0.2 0.3623 0.501+0.2875 0.7867 3) dBs=3dB(b=0.501); SWRc=1.8(c=0.2857); SWRa= ------------ = ------ = 3.65 0.501-0.2875 0.2153 0.4466+0.2857 0.7323 4) dBs=3.5dB(b=0.4466); SWRc=1.8(c=0.2857); SWRa=------------- = ------ = 4.55 0.4466-0.2857 0.1609 5) Stop! Don't panic! A 5 to 1 SWR does'nt hurt anything :) Have fun, a small SWR & 73 de Peter, LZ1LEN lz1len@qsl.net Why don't U send an interesting bul? 73 de John G8MNY @ GB7CIP
Read previous mail | Read next mail