[Amps] SWR and amplifiers

[Roger (K8RI)]

IIRC, SWR = (Forward power + reflected power) divided by (forward power 
- reflected power)
And yes, additional power is lost due to the coax loss and number of 
reflections. IOW the number of times the steadily reduced, reflected 
power makes the round trip. Without going back and rereading the thread 
someone did an excellent job of explaining the loss each time that 
reflected wave traverses the distance from rig to antenna and back.

Again, IIRC there are two modes where a high SWR (lots of reflections) 
might cause problems. Digital and video.
With lossless coax all of the power fed into the coax would be radiated 
by the antenna.
In the real world it's all radiated minus the power lost in the coax. 
The ARRL handbook should have graphs depicting the additional loss in 
coax Vs SWR if you know the coax loss and the SWR.

73, Roger (K8RI)


On 5/25/2017 Thursday 5:24 AM, donroden at hiwaay.net wrote:
> A broke analog clock is right twice a day.
> For it to be right, you just have to know "when" to read it.
>
> If you could insert that same SWR meter at various lengths along your 
> transmission line you might see 200 watts or ZERO watts reflected.
>
> Did your amplifier load or tune change due to this different reading 
> ?  No.
>
> Did your amplifier change power output due to this different reading 
> ?  No.
>
> So what does your swr meter "really" measure ?
>
> We know it measures "something".......... BUT WHAT ???
>
>
>
> Power ( watts ) = voltage x current
> ( or does that apply  in a transmission line ? Hummmmmmmmm   )
>
>
>
>
> Don W4DNR
>
> DonR
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