Hi folks! In Antenna We Trust! All others things are secondary.
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:
dB
|
b
|
RG-213/U
|
RG-58/U
|
dB
|
b
|
RG-213/U
|
RG-58/U
|
|
---|---|---|---|---|---|---|---|---|
0
|
1
|
0 m
|
0 m
|
4.5
|
0.3548
|
56.25 m
|
19.15 m
|
|
0.5
|
0.8912
|
6.25 m
|
2.12 m
|
5.0
|
0.3162
|
62.5 m
|
21.2 m
|
|
1.0
|
0.7943
|
12.5 m
|
4.25 m
|
6.0
|
0.2511
|
75.0 m
|
25.53 m
|
|
1.5
|
0.7079
|
18.75 m
|
6.38 m
|
7.0
|
0.1995
|
87.5 m
|
29.78 m
|
|
2.0
|
0.6309
|
25.0 m
|
8.5 m
|
8.0
|
0.1584
|
100.0 m
|
34.04 m
|
|
2.5
|
0.5623
|
31.25 m
|
10.64 m
|
9.0
|
0.1258
|
112.5 m
|
38.3 m
|
|
3.0
|
0.501
|
37.5 m
|
12.76 m
|
10.0
|
0.1
|
125.0 m
|
42.55 m
|
|
3.5
|
0.4466
|
43.75 m
|
14.89 m
|
11.0
|
0.0794
|
137.5 m
|
46.8 m
|
|
4.0
|
0.3981
|
50.0 m
|
17.02 m
|
12.0
|
0.063
|
150.0 m
|
51.0 m
|
SWRc
|
c
|
SWRc
|
c
|
|
---|---|---|---|---|
1.0
|
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 dBs and SWR at antenna input are actual values vs.
actual frequency and all others (bad)influenced factors.
* For determinating of the antenna cable attenuation, you can use both programms: "Antenna Cable Loss and SWR" or "Antenna Cable Loss and SWR Calculator"
on the address: www.qsl.net/lz1len/projects.html
Examples:
1) dBs=0dB (b=1); SWRc=1 (c=0); SWRa= 1+0 / 1-0 = 1 (Border case, the Dream)
2) dBs=2.5dB (b=0.5623); SWRc=1.5 (c=0.2); SWRa= 0.5623+0.2 / 0.5623-0.2 = 0.7623 / 0.3623 = 2.1
3) dBs=3dB (b=0.501); SWRc=1.8 (c=0.2857); SWRa= 0.501+0.2875 / 0.501-0.2875 =0.7867 / 0.2153 = 3.65
4) dBs=3.5dB (b=0.4466); SWRc=1.8 (c=0.2857); SWRa= 0.4466+0.2857 / 0.4466-0.2857 = 0.7323 / 0.1609 = 4.55
5) Stop! Don't panic! A 5 to 1 SWR does'nt hurt anything :)
Have fun, a small SWR and 73 de Peter, LZ1LEN, www.qsl.net/lz1len
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