SWR - the big mistery...

One of a good friend of mine asked me to explain what SWR is. It is so easy to explain until a certain point of counting... 

To make it easier I created a table to show how VSWR, reflected power and impedance are related to each other. 

Here it is:

Load (ohm)	SWR	Return loss
10	5	44.4
15	3.3	28.6
20	2.5	18
25	2	11.1
30	1.66	6.2
33.3	1.5	4
35	1.4	2.8
40	1.25	1.2
45	1.11	0.3
50	1	0
55	1.1	0.2
60	1.2	0.8
65	1.3	1.7
70	1.4	2.8
75	1.5	4
80	1.6	5.3
85	1.7	6.7
90	1.8	8.2
95	1.9	9.6
100	2	11.1
110	2.2	14.1
120	2.4	17
130	2.6	19.8
140	2.8	22.4
150	3	25
200	4	36

It is so easy. Read the VSWR value on your meter or display. In case of 50 ohm transmission line (most radios have 50 ohm output) if the load is 50 Ohm, efficiency is 100%, therefore loss is zero. It means no wasted power is heating the final transistor of our transceiver. 

As load starts differing from the 50 Ohm, VSWR will increase. Most transceivers are happy until VSWR 2. In this case slightly more than ten percent of our power is wasted. For example if  we transmit 100Wtts, we will lose 10 from that. 

VSWR should be kept as low as possible tuning the antenna or using coupler called antenna tuner, or matcher. 

It is not rocket science, even there are few more formulas in the background of the story. If one doesn't want to go too deep, this table is enough.

Have fun, and keep tuned!