[TowerTalk] Probably dumb question

[jimlux]

On 8/14/18 9:19 AM, k7lxc--- via TowerTalk wrote:
>      If there are 100 watts out and 10 watts reflected, what's the swr?
>   
>      If there are 200 watts out and 10 watts reflected, what's the swr?
>   
>      Tnx.
>   

Since SWR is the ratio between high and lowest  "voltage", you need to 
calculate that.

For a 50 ohm line, 100W is 70.7 V, the 10W reflected is 22.4V - so max 
voltage is 70.7+22.4 =93.1 and min voltage is 70.7-22.4 = 48.3 so VSWR = 
93.1/48.3 or 1.93

(the answer is impedance independent.. I just used 50 for an example)

This is handy to remember a 2:1 is about 10dB return loss  (actually 
it's 9.5 or something...)  1.5:1 is about 14 dB




For the 200W and 10W case the forward voltage is 100V, the reverse is 
22.4 so it's 122.4/77.6  = 1.58

(this is 13 dB return loss, so it's a bit worse than 1.5:1, which would 
be 14 dB)