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G8MNY  > TECH     21.10.18 09:00l 115 Lines 4488 Bytes #8 (0) @ WW
BID : 42434_GB7CIP
Subj: Actual Antenna SWR
Path: ED1ZAC<ED1ZAC<IZ3LSV<IK6ZDE<I0OJJ<GB7CIP
Sent: 181021/0653Z @:GB7CIP.#32.GBR.EURO #:42434 [Caterham Surrey GBR]

>From g8mny%gb7cip.#32.gbr.euro@i0ojj.ampr.org Sun Oct 21 08:54:21 2018
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>From: g8mny@gb7cip.#32.gbr.euro
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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



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